Measurement and Modelling of Noise Emission of Road Vehicles for Use in Prediction Models

Home , Sound exposure, Sound power, Sound pressure

Hans G. Jonasson

Nordtest Project 1452-99 KFB Project 1998-0659/1 997-0223

-..

SP Swedish National Testing and Research Institute SP Acoustics SP REPORT 1999:35 .—

Abstract

The road vehicle as sound source has been studied within a wide frequency range. Well defined measurements have been carried out on moving and stationary vehicles. Measurement results have been checked against theoretical simulations. A Nordtest measurement method to obtain input data for prediction methods has been proposed and tested in four different countries.

The effective sound source of a car has its centre close to the nearest wheels. For trucks this centre ,seems to be closer to the centre of the car. The vehicle as sound source is directional both in the vertical and the horizontal plane. The difference between SEL and LpFn,aduring a pass-by varies with frequency. At low frequencies interference effects between correlated sources may be the problem. At high frequencies the directivity of tyre/road noise affects the result. The time when LPF.,Uis obtained varies with frequency. Thus traditional maximum measurements are not suitable for frequency band applications.

The measurements support the fact that the tyreh-oad noise source is very low. Measurements on a stationary vehicle indicate that the engine source is also very low. Engine noise is screened by the body of the car. The ground attenuation, also at short distances, will be significant whenever we use low microphone positions and have some “soft” ground in between. Unless all measurements are restricted to propagation over “hard” surfaces only it is necessary to use rather high microphone positions.

The Nordtest method proposed will yield a reproducibility standard deviation of 1-3 dB . depending on frequency. High frequencies are more accurate. In order to get accurate results at low frequencies large numbers of vehicles are required. To determine the sound power level from pass-by measurement requires a proper source and propagation model. As these models may change it is recommended to measure and report both SEL and LpFnlanormalized to a specified distance.

Key words: Noise, emission, road vehicles, measurement method, source modelling

Swedish National Testing and SP Research Institute SP Rapport 1999:35 SP Report 1999:35 ISBN 91-7848-794-3 ISSN 0284-5172 Bor5s 2000 Postal address: BOX 857, SE-501 15 BO~S, Sweden Telephone +46 33165000 Telefax +4633 135502 e-mail: info @sp.se http:llwww.sp.se DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are “ produced from the best available original document. Contents

Abstract 2 ,,”

Contents 3

Preface 5

Conclusions 6

1 Introduction 7 1.1 Aim and background 7 1.2 List of symbols 7 1.3 Some basic theory 7

2 Some preliminary considerations 10 2.1 General 10 2.2 Source height 10 2.3 Ground interference and instantaneous sound pressure levels 10 2.4 Interference effects and SEL 13 2.5 Meteorology 14 2.6 Discussion 14

3 Some pass-by measurements on single vehicles 15 3.1 General description of the measurements 15 3.2 Vertical directivity and interference effects 17 3.3 Distance dependence 20 3.3.1 Sound exposure level 20 3.3.2 Maximum sound pressure level 22 3.4 Engine noise versus tyre/road noise 24 3.5 Integration time 26 3.6 Time history 26 3.6.1 Car 26 3.6.2 Truck 28 3.7 Ground attenuation 29 3.7.1 Sound exposure level 29 3.7.2 Maximum sound pressure level 33 3.8 Aerodynamic noise 36

4 Some measurements with parabola 38

5 Some further measurements 41 5.1 Measurement site 41 5.2 High exhaust 41 5.3 Screening of engine noise 42 5.4 Measurements with a barrier 43 5.5 More examples at another test site 45

6 Measurements on stationary vehicles 48 6.1 Description of measurements 48 6.2 Analysis of the results 48

7 Determination of SEL, LpFmaxand Lw 51 51 7.1 Difference between SEL and LpF.a . ..-., . . . __Q...L2.2. .~. . . —.. .- ?..

7.2 Calculation of Lw and LpFmx 52

8 Discussion and conclusions 55

9 Comparison measurements using Nordtest method 56 9.1 Introduction 56 9.2 Results 57

10 References 61

Annex Proposal for Nordtest method 63 5

Preface

The work accounted for in this report have been financed by 3 different projects:

Nordtest project 1452-99 Measurement of noise emission of road vehicles has financed the comparison measurements and the elaboration of the Nordtest method, Swedish Transport & Communications Research Board (KFB) project 1998-0659 New Nordic prediction method for road trafic noise - Acoustic source modelling of road vehicles and KFB project 1997-0223A new test method for the noise emission of cars .,, have financed the other measurements and the theoretical work. In addition everything ,.- .- has been discussed and planned within the frame of the current Nordic project Nerd 2000 !’ aiming at making a new generation of prediction methods for environmental noise.

The following people have been actively involved in the projects:

Steind6r Gudmundsson, Icelandic Building Research Institute Jorgen Kragh, Birger Plovsing, Delta Acoustics & Vibration, Denmark Svein Storeheier and Truls Berge, SINTEF, Norway Juhani Parrnanen, Technical research Centre of Finland Hans Jonasson, Tomas Strom, Geir Andresen and Xuetao Zhang, SP Swedish National Testing and Research Institute.

Volvo Truck Corporation supplied a truck with driver for some of the tests.

The help of the above individuals and organizations are gratefully acknowledged.

Most of the work was earned out in 1999 but the report was not finalized until December 2000.

Bor%, December 2000

Hans Jonasson

. — —— ,. e-r, ...... ,. - ..- 6

Conclusions

The effective sound source of a car has its centre close to the nearest wheels. For trucks this centre seems to be close to the centre of the car.

The vehicle as sound source is directional in the vertical plane. Between 100 and 800 Hz there seems to be some decrease of sound at all positions above the bottom of the car body. This is probably due to screening of the engine. At high frequencies there seems to bean increased directivity upwards. Both effects seem to be less than about 2 dB for distances and heights practical to use for emission measurements.

The vehicle is also directional in the horizontal plane. The difference between SEL and LPF.Uvaries with frequency. The time histories of pass-bys verify such a frequency dependence. At low frequencies interference effects between correlated sources maybe the problem. At high frequencies the directivity of tyre/road noise affects the result. The time when LPF.U is obtained varies with frequency. Thus traditional maximum measurements are not suitable for frequency band applications.

The measurements support the fact that the tyre/road noise source is very low. Measurements on a stationary vehicle indicates that the engine source is also very low. It seems that a source model using three different point sources yields reasonably good results. For passenger cars the three sources can be used throughout the frequency range. For trucks, however, the lowest source should only be included above 2000 Hz. At high frequencies there are large statistical variations.

The significant frequency dependence of the difference between SEL and LPF~mmakes it difficult to measure only one of the quantities. Nor is it easy to calculate one quantity from the other. In order to be able to do so we need an accurate source model. Such a model is also required to calculate the sound power level.

The ground attenuation, also at short distances, will be significant whenever we use low microphone positions and have some “soft” ground in between. Unless all measurements are restricted to propagation over “hard” surfaces only it is necessary to use rather high microphone positions.

To determine the sound power level from pass-by measurement requires a proper source and propagation model. As these models may change it is recommended to measure and report both SEL and LPFn,mnormalized to a specified distance.

The Nordtest method proposed will yield a reproducibility standard deviation of 1-3 dB depending on frequency. High frequencies are more accurate. In order to get accurate results at low frequencies large numbers of vehicles are required. 7

1 Introduction

1.1 Aim and background . ,.- The aim of Nordtest project 1452-99 Measurement of noise emission of road vehicles is to define a measurement method suitable to use to obtain input data for road vehicles in prediction methods.

The aim of Swedish Transport& Communications Research Board (KFB) project 1998- 0659 New Nordic prediction method for road trafic noise - Acoustic source modelling of road vehicles is to describe the road vehicle as one or more point sources which may either be omnidirectional or have a specified directivity. In combination with point source sound propagation theory traffic noise can the be calculated accurately.

KFB project 1997-0223A new test method for the noise emission of cars aims at analyzing problems with the current noise emission method ISO 362, [3], in relation to practical trafllc noise conditions. The results of this project reflects the fact that the original budget was cut by 50%.

The first two projects are essential for the Iongterm Nerd 2000 project which aims at new prediction methods for environments noise, including road traffic noise.

1.2 List of symbols a, d= the shortest distance to source (m); C(v) = calculated difference between sound exposure level and sound power level h,, height above ground of receiver; h$,height above ground of source; LE, sound exposure level (dB); LPF~u,maximum sound pressure level with time weighting F, Lw, sound power level, in dB; n, number of sources; p, sound pressure (Pa); t,time (s); P, sound power (W); v, speed (m/s); ALi = the increase in sound pressure level due to the presence of a sound reflecting ground surface (dB); cz open angle (radians); Z time constant (s);

1.3 Some basic theory

Assume that each vehicle has n different omnidirectional sources, each emitting a different sound power Pi. When passing the microphone, ignoring all excess attenuation in excess of free propagation and possible ground interfere~ effects, each source will yield, see e.g. [7], the sound exposure level LE;

LE,i = Lpmx,i+ 10lg(tr) – 10lg(v) + 10lg(Ad) (1.1) . . —.-. —— ,.

where a= the shortest distance to source i (for simplicity a is assumed to be equal to all partial sources), v= the speed (m/s) and zla= the sector angle (radians) covering the time of integration, see figure 1 LP~m,jin (1. 1) is the true maximum measured with a very short time weighting.

v ------1 ~------I 1 (-----J ,1------I \ u / . / ‘\ /’ . I 1 /’

Figure 1. Basic geometry of a pass-by

Eq. (1.1) also gives the difference between sound exposure level and maximum level in the ideal case with no excess attenuation:

LE,, – LPmx,i = 10lg(a) –lOlg(v) +lOlg(Acz) (1.2)

The total LEfrom all partial sources is obtained by adding all the different contributions on energy basis. Thk adding can be carried out automatically by measuring the sound exposure level, LE, during a complete pass-by by all partial sources of the vehicle.

For an omnidirectional source Lp~a,iis given by

L,mx,i = Q,i -101g~z(a2 + (h, - h~,i)’)]+ AL, (1.3)

where LIK,= the sound power level of source i, h,= the height of the receiver and h,,, = the height of the source i. ALi is the ground effect which can take any value between -CO and +6 dB depending on the geometry, the ground surface and the phase relationship between the direct and the reflected wave. If the difference in travelled distance between the direct and the reflected wave is small compared to the wave length and the ground is totally reflecting, ALi = +6 dB. This is for instance the case at all low frequencies, even if hs is great when h~is small or, for all frequencies at all receiver heights, if h~is close to zero. In these two cases we get approximately by assuming that h/a

4,= LE - lolg(a) + 10lg(v) - 10lg(A~) + 101g{4m(a2 + h:} -6 (1.4)

In practice eq. (1.4) will be complicated. A complete source and propagation model has to be used in order to predict the sound power model from a pass-by measurement of the sound exposure model.

In the following the notation C(v) will be used for the difference between sound exposure level and sound power level: c(v) = LE – Jq (1.5)

The notation C(v) is used to indicate that C is a function not only of frequency but also of speed. From (1.4) we can see that, for a given spectrum

c(v) = C(vo) + 101 ~ (1.6) {)Vo where V. is the reference speed for which C has been determined using the source model.

At noise emission measurements the maximum A-weighted sound pressure level during pass by is often interesting. Normally time weighting F as defined in IEC 651 is used. However, in the Nordic countries time weighting S is also often used. Because of this confusion it is of interest to calculate the maximum level with different time weighings. By definition the time weighted sound pressure Ievel is given by

Lp(to) = 10lg ~~~e1 ‘0P2(0 (Ho)/T~t (1.7) [ 1 where the time constant z= O,125s for time weighting F and 1,0s for time weighting S.

Assuming we have a source consisting of a number of point sources, for example wheels, each wheel, will contribute, neglecting the ground attenuation, according to

p’(t) = 10%/10 (1.8) P: 2z(a2 + (vt - dl~)’)

where Llyflis the sound power leveI of wheeI n. v= the speed of the vehicle, ciln=the distance between the first wheel(n=l) and wheel no n. t= Ocorresponds to the first wheel being closest to the receiver.

— . >.<.,...... —,, 10

2 Some preliminary considerations

2.1 General

The aim of the Nordtest project is not only to get reproducible but also correct measurement results as well. It is, e.g., possible to get reproducible results by specifying measurement distance and microphone height with narrow tolerances. However, if these parameters cause systematic errors which are not known, the results cannot be used for input into accurate prediction models. The problems to overcome are much more difficult now than they were in the past when we worked primarily with A-weighted sound pressure levels, but now the aim is to work with one third octave band calculations.

Current prediction models use several different source heights. Some examples: In [1] 0,5 m is used for A-weighted sound pressure levels and in [2] both zero height for tyre/road noise and 1,8 m for the other noise sources is used. Logically the truth must be more complicated than that. As will be obvious from the following the selection of source height is critical. The problem is also difficult as we may have to use several different source heights combined in different ways depending on the relative strength of the sources.

For practical reasons the number of microphone positions for standard measurements should not exceed two in order to make it possible to use conventional 2-channel real- time analyzers.

2.2 Source height

A vehicle has several different noise sources: tyre/road interaction, engine, transmission, air intake, exhaust, aerodynamic noise, body and wheel vibration. The tyre/road source is very low, close to O.In [8] it is concluded that the source is between 0,01 and 0,05 m and no distinction is made between engine and tyreh-oad noise. In stead the conclusion is drawn that engine noise, if any, is also emitted from under the car. In different prediction models engine noise is often assigned a source height which may vary between a few centimetres up to several meters for large trucks. It is important to find a measurement procedure which can deal with all these source heights. Tyre/road noise is dominated by frequencies above 500 Hz while the other sources are more important for the lower frequencies. It must also be considered that tyreh-oad noise, although normally dominating, may be less important if there are low screens close to the vehicle.

2.3 Ground interference and instantaneous sound pressure levels

The method should not have any bias for any frequency band between 25 Hz and 10000 Hz. This is a rather tough requirement. Interference between the direct and the ground reflected sound wave will always depend on source height, measurement distance and receiver height as well as on the properties of the ground between the vehicle and the receiver.

The problem is illustrated in figure 2 which shows clearly that if we have a high sound source, in this case 1,0 m, the commonly used microphone position at 1,2 m, used in [3- 4], above ground yields substantial systematic errors at 250 Hz and above. If, in stead, we 11

select a low microphone position, the problems move upwards in frequency, see figure 2. Obviously the low position is more predictive. However, it will have problems with the ground attenuation. Both figures assume perfectly reflecting ground. The calculations have been carried out using “smoothing” according to [5] for one third octave bands. The car propagates along a line from-50 m to +50 m and passes the microphone at x= Om.

5’ 72

66 -40 -30 -20 -10 0 10 20 30 40 m Figure 2. Instantaneous sound pressure level during pass-by, third octaves, source height 1,0 m, receiver height 1,2 m, distance 10 m. caI-pass(20,1,0,10,1 .2,k3

5 / 72 \

70 “ y ... 68 F’

66 -40 -30 -20 -10 0 10 20 30 40 m Figure 3. Instantaneous sound pressure leveI during pass-by, third octaves, source height 1,0 m and receiver height 0,1 m. caI-pass(20,1,0,10,0,1, k’)

As the source height is not known and may vary from vehicle to vehicle, at least for engine and exhaust noise, the most logical choice of microphone position would be to have one position on the ground yielding +6 dB relative sound propagation in a free field corresponding to the example in figure 3. This ground position is rather unproblematic for low frequencies but sooner or later the ground attenuation wilI affect the resuIt as the frequency increases. It is necessary to identify the lowest frequency to yield +6 dB. As will be shown later this position also has the advantage of keeping wind noise at a minimum.

.—— 12

If the microphone height is increased we get other effects which are illustrated in the following figures. Figure 4 shows that for a high source, 1,0 m, and a high receiver, 4,0 m, there are strong, unpredictable interference effects below 1000 Hz but at and above this frequency we get a more predictable result approaching +3 dB relative the free field sound pressure level.

80 f , 1 z

I ~ i 76 - i 1

74 I .5’ ! I

! 1

68-

-40 -30 -20 -lo 0 10 “20 30 40 m Figure 4. Instantaneous sound pressure IeveI during pass-by, third octaves, source height 1,0 m and receiver height 4 m, measurement distance 10 m. carpass(20,1,0,10,4,’n’)

Now the question is what will happen when the source is very low, like the tyre/road contact point which may be close to O.This problem is illustrated in figure 5 and 6 for the receiver height 4,0 m and 1,2 m respectively. Obviously we are back to the same interference problems as we had for low frequencies at 1,2 m microphone height. The figures are, however, purely theoretical products. In reality we may have severaI different source heights “smoothing” the result. Experimental results have to be analysed before any conclusions can be made.

80 , a # ,

I 78

76 -

74 “ ] 5 72

66 -40 -30 -20 -10 0 10 20 30 40 m I?igure 5. Different low point sources with a high receiver. 13

80 , 1oocj Hz

74 -

5 72 i

I 66 -40 -30 -20 -lo 0 10 20 30 40 m Figure 6. Different low point sources with a medium high receiver.

A comparison between figure 5 and 6 shows that the interference effects are greater at high frequencies for high receiver positions. This is a problem as low positions may give too much ground attenuation.

2.4 Interference effects and SEL

Infigure 7 and 8 some examples for the sound exposure level are shown. Figure 7 illustrates that the problems are small when the source height is 1,0 m. We have a rather nice +6 dB case close to the ground and an equally nice case at 4,0 m.

95 ,, -

94 ,’,,

m -0 ~-92 C/Y ,-‘. 91

89 . 10’ 103 104 Frequency, Hz Figure 7. Source height 1,0 m. Measurement distance 10 m. Different receiver heights.

Figure 8, however, indicates the problem with a low source height. The only predictable height is 0,0 m which cannot be used in practice because of possible ground attenuation.

------,.. .,>7-- ..,. ,. -...... ?.,.. .- ,. .. . T> ..,,,_, ... ., - —————. . . .. —. .

95 I I I 1 , , t k

m u

Ii Ii

89 102 103 104 Frequetwy, Hz Figure 8. Source height 0,1 m. Measurement distance 10 m. Different receiver heights.

2.5 Meteorology

Wind induced noise is critical at low frequencies, in particular for ordinary cars which emits mainly high frequency tyre/road noise. This fact is another reason to select a low microphone position for low frequencies. The wind speed is significantly smaller close to the ground.

2.6 Discussion

It is obvious that low frequencies are best dealt with using a low microphone position and very high frequencies using a high position. However, the most important medium high frequencies are more difficult to deal with. Experiments are needed to get the best solution. One problem with high frequencies may be the directivity. If high microphone positions are used the sound pressure level measured may not be representative for more horizontal propagation. 15

3 Some pass-by measurements on single vehicles

3.1 General description of the measurements

All car and truck measurements have been carried out on a flat air field using an asphalt runway with surrounding grass land. The asphalt surface was very hard. As the car generated rather little low frequency noise the sound exposure levels below 250 Hz are not always reliable, at least not for the high microphone position. The truck used was a Volvo FH 12 heavy truck with and without a 3 axles trailer, see figure 8 and the car used was a new vw Passat. station car, see figure 10. unless otherwise indicated each measurement represents the energy average of 3-5 pass-bys. The microphone arrangements can be seen in both figures. The special ground microphone very close to the ground is shown in figure 11.

I .

.,; -a’. “. ,.. :., ,,...... ’ ...... ,, .j ., . . .. ,’ .,, . ,.. ‘j ..< , .,.’ ,. >,, ,,. . .’ ,.:,,, . ...,, ,., ~:, ,., :.,...- ,’ .. ., . , :.,.,,..,., . . . ,z- .“ t i.’, ,.... -., , ,,A_“._>Ar.--->:”. .&,. -; 4.. ‘ ...... ,. < J--- -.s-.:. . . -’[ Figure 9. The Volvo truck used for the measurements

. . . —-4 .——— —.

.. ,,...... 1:. ‘: , ,,. ,,. ,: . . . ‘, T

Figure 10. The VW Passat used for the measurements

Figure 11. The ground microphone 17

3.2 Vertical directivity and interference effects

Car, 50 Imr/h, 3 m 96,0. , , , , , # , , , , 94,0 -- 1 -J--L-J--I-.-L-J-- L -J--l--J-l--l--J--l_- L +0 .L --I.- 1111111 !Ilt 11 -+ --l--> -+ --l--+ --l --+-+ --1--1- -m- 0,4m -+ --l------~- - +--;--}-+--:--;-+ --:-- +--:--.: +0,8 +_ -;-- 88,0 L -J--L--I-.-I-- L --I--L-2-J-- L –x-- 1,2 ------

84,0 %?,0 :!:!:$:: :; :!:::: 80,0 --- _r _~ .: --:- 78,0 --L - L--I--I--L-A - 11111 -..-;, 1 m 78,0 ‘o J 74,0 _-lL 1 1 l\ll 1 I % 720 --1- L.--i---i-x--t--i--l . -_, 1- - ;_- + --;-- : - + --:---- + --;-- } - + --;-- + --; -_:-- + - ‘- . -:-- 70,0 -+--1 ‘ - -w I @aco -4--1-- ‘N -A--l--+--l-- I--4--I--+--!-- I--4--I--*--I--!- -4--1-- -a.+ --i-- 8 1111 Ill 1111 11 E8,0 -T--;-- ~-,_-r-T--:-- ~-7--r-,_-:__:_n F r-~--l--~-~-- }-J--j-- Y \ -r-- -- r34,0 - .1--l--_l_L--L-l-J__ L-J--I-- L--I--L-J--I--L-J--I- -1--1--L-J-N L--l - 1111111 111!111 1111111 1., “,., eo -n--l-- r-q--r-t--,-- ~-q--,--~-q-- p-,--,--r-<-- ~-T--,-_r-q-J ‘\ - ;- 00,0 -+.--;--+-+.--}.-+.--;-- +-;--;--+--;--}-+--:-- ;-;--:--{--:--}-;--:--w , +-- -- m,o [ -4--1--J---I--I- -b--l--l--J--l-- A-A--L-4--I-- J.--I--L-4-A-- l__4-A-i!Y\

Figure 12. Carpass-byat3 m. Propagationover asphaltonly. Thezeroheight microphone is 0,5 m from the nearest wheel whereas the 3 m distance is measured from the centre line of the car, that is 2,25 m from the nearest wheel.

Figure 12 illustrates that the SEL-level drops off when the direct distance increases. The ‘ ,- smaller difference at high frequencies indicates an upwards directivity at high frequencies or, alternatively, screening of low frequency engine noise. The theoretical fall off of 10 Ig(distance) is illustrated in table 1 assuming that we have a point source, integrated during its pass-by, on the road surface under the middle of the car. The results indicate that the major sound source is rather at the distance 2,25 m than 3,0 m, that is ... the nearest wheels are the most important sources. The astonishing results below 100 Hz are probably due to wind induced noise from the vehicle pressure wave. : ...

Table 1. Distance dependence of SEL at the distance a and the height h,. a ~olg(T) ‘r a ,O,g(m) 2,25 3 0,0 0,4 2,25 0,1 3 0,1 0,8 2,25 0,3 3 0,3 1,2 2,25 0,5 3 0,8 2 2,25 1,3 I 3 1,5 I 3 I 2,25 2,2 3 2,2 4 2,25 3,1 3 2,9 5 2,25 3,9

---- -..- ., ...... —.-. —--ma... .—

Truck without trailer, 70 kmlh, 3 m 100.0. I , r , , I , c , 1 98;0 96,0 94,0 92,0 90,0 88,0 86,0 64,0 82,0 80,0 m v 78,0 2“ 76,0 w f.e 74,0 72,0 70,0 68,0 66,0 64,0 62,0 60.0

Frequency, Hz

Figure 13. Truck pass-by without trailer at 3 m distance with the exception of the zero height microphone which was about 0,5 m from the nearest wheel.

Figure 13 shows that the behaviour of the truck is very close to that of the car. The only major difference is that the close to zero height microphone has much higher values at low frequencies which is an indication that engine noise is relatively higher for the truck.

Figure 14 shows a bus pass-by at a short distance. The 4,5 m microphone position seems to give about 2 dB lower levels at low frequencies. Qualitatively this is in agreement with the theoretical calculations for a longer sound path. Thus the screening effect, if any, seems to be lower for the bus than for the other vehicles.

Distance: 4,9 m

88 ------______-______---=f::;l 86 ------64 ------Ml

_. $ 78 ------= 76 ------ar ~ 74 ------: 72 ------~ 70 ------~ 68 ------3 66 ------(%64 v~ ------~ 62+--- _------__---- ___--- ____---______-______-\~____{ 6O}------>~--{ 56+------‘------‘-----\W

Frequency, Hz

Figure 14. 2-axles buspass-by. Sound exposure 1evel. 19

Distance: 7,5 m ‘.

76- - .------

u _- 70~ al ~> 681 ~ 66- - L $ 64------!j 62- - : 60+------&~------j c 56}------>}------+ 3 r??

52 ------,------50

Frequency, Hz

Figure 15. 2-axles bus pass-by. Soundexposure level.

Figure 15 also indicates thatthe lowfiequency SELisl-2dB lower atlowfrequencies at 4,5 m than it is at 1,2 m. At high frequencies ground attenuation affects the result. In figure 16 the difference in pathlengths to the two microphone positions is negligible but still the 4,5 m microphone yields about 1 dB lower values, which may support the screening hypothesis.

Distance: 22,1 m

60- 76- - 76- - 74- - 72- - 70------~- 66 ~ 64 0 62- - : 60- - $$56- - =56- - u e54- - s 0 52- - m 50- - 48- - 46------44- - 42------40 T

Frequency, Hz

Figure 16. 2-axles buspass-by. Sound exposure level. . . ..

3.3 Distance dependence

3.3.1 Sound exposure level

-1.25 -0.75 0.75 1.25 1.65 265 4.15 5.65 Figure 17. Test set up

Car pa.ssby at 70 Ianlh, different dlsbnce% O height 78,0-

76,0- - -- +---.;___ ;---+--+ --_; ---lr -.-:__-\------:---+- -+ ___ 74,0- - -- ~ ---l ---l--- I.---I--A---L- -L _- -4 _ --l------1---

-v--_-_-

~. - + ---l ---l--- +--+-

58,0- -

56,0- -, --1---1 __ -l___ 81111 11111 11 54,0- - 11 11 52,0- -“ --AT--,-__’--- 50,0- -“;;;;------__-’___ Hxk’[ ;;;;;:,+!::~:: &:- II 48,0- - --J--4---I--- L--4--..1---I- --4---I---I- --L-- 11 1111 tl Ill 46,0- - --T--T__-;--- r--~---l---r--J__ ~---_;-;__..;__ ~---l--_r--;___ 44,0, I I I I I ! I I I I I I I I I I g~gggg~ $ ~~ j j~ g $Zsg

Frequency, Hz Figure 18. C~pass-by withzero height microphone atdistances shown in figurel7. Simultaneous measurements at all distances.

A comparison between figure 18 and the calculated distance attenuation 10 lg(distance) given in table 2 for the distances described in figure 17 shows that the sound source giving the best fit is not the car centre line but the nearest wheels. These measurements confirm the results shown in figure 12 and table 1. The results are confirmed by figure 19 which shows the same car at 90 kmih.

Table 2 Calculated distance dependence of SEL in figure 18. K2=1,65 K2=0,90 K3=2,65 K3=1,90 K4=4,15 K4=3,40 K5=5,65 K5=4,90 10 lg(K3/K2) 2,1 3,2 10 lg(K4/K2) 4,0 5,8 10 lg(K5/K2) 5,3 7,4 21

Car WAY at 90 Ian/h, different distance% O height 00,0. , 8 , I I , , , 4 . . ------II II 78,0- - 11111 Ill -. -..+--- :- __\__ ; --..-:--- + --.-:---- I_

,,.-

~ 6s,0

111111 1 60,07 --;

5a,o \! 58,0 --;---:---;--;---:------j ; ~ ; ; --;--.~--.+.--;--+;___;___‘ lr__ +.--_;---- ;--;--+__;-Ir -- + -__:___ } -- -- _;-_:, --

54,0 --, 1---I---L--J---L--1, --J---Ll-l---l--_L__ J_-_!-_-L_-J- -L- II 11111 111!1 11 52,0 -- J---_L-JL--J---L --L--J---I---L ---I---L--J---I--- L---l--- \ -- Illt 11111 1!111 I .500“11-- + ---,--- 1- -- -1 ---!- -- + -- +---+ -- + -- +---- # -- + ---,___ * -- \+ -__,_-

Frequency, Hz

Figure 19. Cupass-by withzero height microphone atdistances shominfigue2O. Simultaneous measurements at all distances.

In figure20andtable 3thecorresponding informationisgiven fortheVolvotruck. In this casethe best fitseems tocome fromhaving the truckaxis asreference forthe distance.

Truckpass-byatdiffemnt dlsemc%satas+eed of70kmlh and mlcmphone height 0,4 m 92,0 90,0 ea,o M,o %0 02,0 60.0 78,0 76,0 74,0 ~ 7Z0 ~ 70,0 ~ Ixoo 66,0 64,0 02,0 00,0 50,0 56,0 54,0 52,0 50,0 48,0 a;$l s ~% ~ ~ g g! : $$s33gggggggggggj

Frequency (Hz)

Figure 20. Truck pass-by at 3 different distances with microphone height 0,4 m. i .

Table 3 Calculateddistance dependenceofSEL infigure20. K2=3 K2=2 I I K3=6 I K3=5 I

In figure 21 thecorresponding figure for4mreceiver heightis given.

,—--..,.. _ ...... !.-...... , ,., ...... —. .—— -. -— ———-----

Truck pass-by at different dl-nces at a speed of 70 kmlh and microphone height 4 m 90,0 660 %,0 64,0 62,0 60,0 78,0 76.0 74,0 ~ 72,0 g 70,0 ij 66,0 @ 66,0 64,0 62,0 60,0 66,0 66,0 54,0 52,0 50,0

Frequency (Hz)

Figure 21. Truck pass-by at 3 different distances with microphone height 4,0 m.

Figure 20 and 21 indicate that the major sources for trucks at 70 lm-dhare close to the centre of the vehicle.

3.3.2 Maximum sound pressure level

Carpasbyat70km/h 620 , , i i I , 0 , 8 60,0- --- 7a,o. - -_; _--:___l T . --- 1l --- I r -- ;__-:---- )-

l---ti L- J___l__l_ --l -- J--_ L__ J _--L---_--J-_ _L -_

58,0- - -- i---l---r-- -1 --- l---t---, --- l--- q---,- --f---l---p- -% ---, 66,0. -,,-- J--- 1---!. ,, ---l --- l___L ___l --- 111111 1111. , 54.0- - 52,0- - -- +--- :---!. ---1-__ l___i ___l _- -L -- J___ l___L ___l _ -- l--- J___ l_-, _L __ 11111 1111, ,,, ., 50,0- ---+---l---*--1---1- -- + ---l --- l--- +---,--- + ---, --- l----f ---,- --’ f.,-- 4,0- --- + ---; --- + --:---:--- +---~---;--+---;---:- --; ---: --: ---: ---:--- i 40,0 * / g~gg::~~g ~g~ $gg~gg . . Fraquency, Hz Figure 22. Carpass-by withzero height microphone atdistances shown in figure2O, Simultaneous measurements at all distances. 23

...... Table 4 Calculated distance dependence of LPF~musing 6 dB/doubling. K2=1,65 K2=0,90 K3=2,65 ~ K3=1,90 K4=4,15 K4=3,40 K5=5,65 K5=4,90 20 lg(K3/K2) 4,1 6,4 20 lg(K4/K2) 8,0 11,6 20 lg(K5/K2) 10,6 14,8

Table 5 Calculated distance dependence OfLpmu using eq. (1.8) and (1.9).

. K2=1,65 . K2=0,90 K3=2,65 K3=1,90 K4=4,15 K4=3,40 K5=5,65 K5=4,90 LoF.u(K~-Kz) 3,1 4,7 LP~ma(G-Kz) 6,3 8,7 L.c. ....K.)-K.) 8.7 11.4

It seems to be difficult to draw any firm conclusions from these measurements and calculations. The point source description is probably not accurate enough. However, also in this case the shortest distance to the car seems to come closest to the truth. The problem will be discussed further later on in this report in connection with directivity and time-history during pass-by. ,,

Carpa*yat671an/h 6?,0 - , a m,o -

-r --,--

~ Es,o --1 -- - 1- .-...&’=-$__

~ 61,0- - \l S3,0 . -;;_ ------: ---: --.-; -- + --.-;---; - .- .-:---.; _ -;_--;--- ;------N %,0 . - 54,0. --- L--J--J---I---L--1- -J--J__-L-- S2,0 - - _ - ; -- ; ---.: --_;- 520. - -- > ---1 ---1 ---1--- L - .- A ---I ---1--- I--- L -- J. ---I ---I--- 40,0. - .-- + --+-.-._; -.-- ;---+ -.-+.-..-:- --: ---;--- :-- +-.-+ ---; ---;---- +-- +-.’-. 46,0 ‘1 gg~g~~gg~ gg~ $$$$$: F- Fraquency, Hz Figure 23. Car pass-by with zero height microphone at distances shown in figure 17. Simultaneous measurements at all distances. .— ,= ——- .“

3.4 Engine noise versus tyre/road noise

Figure 24 was measured in 1999 and the following figures in 1998.

Car paaa-by with and without engine ewitched on 78,0 i , , , , , , , I Ill 111 11111 76,0 -- 7--7---.,---.;-- ~__ ‘cr -- ., .---,--- ,--_ r_- J 74,0 72,0 70,0 68,0 66,0 64,0 I — -fL:-w.# II KWoff _ % 62,0 L-_4--*-_ -l---L- -- 11 !11 ~ K410ff ~ 60,0 L --l---l-- _l_--L_ —-- Ill ,, _ KYoff - 58,0 L--l ---1------L- -- Ill 11 --x--K2/on - 56,0 --_l ---l___ L-- 1--J-- -l---L- -- 11 Ill 11 -+-KWon - 54,0 _--l ___ L-- ---1! ---l-- -1---1- - --+-KUM - -- 11 Ill II 52,0 -- d--- l--- L-_l- --1-- +_- l------KYon- -- 11 Ill 1 ------I ;--- --_+--_;1 -- -,---1 l-- - + --_: ---;- -- 50,0 I 1 1 I I L1 ------;------+---: -- - + _--; ---:- -- 48,0 1 1 ---l1---:---;-._;.---.: -- - ~ --_:--- :_ -- 46,0 .- 44,0 J 1 I I I I 1 I I I I I I I I I I

Frequency, Hz

Figure 24. Cmpass-by with(70 M)mdwithout (67~)engine switched on. Simultaneous measurements with microphone height: 0,0 m. Propagation over asphalt.

Figure 24 shows very little difference between engine/on and engine/off which indicates that tyre/road noise dominates.

Car, engine switched off, 70 kmlh, 3 m 86,0 84,0 82,0 80,0 78,0 76,0 74,0 72,0 70,0 88,0 66,0 64,0 > 62,0 y_-:-y-;__:-.:-:__;_-*-y 60,0 58,0- -- L --I--I--L-J--I-- L-J--I--L-J- 56,0- - J------+-’--’-l--’--’-l--’--’-” -W::~:W::[:::::: :;::~:j::~::~:j::~:: ~:j::[::~:j::::_ ~:fi ‘ ‘ 54,0- - 52,0- -,,-l--l -- L_ J--l--,,, L- 1, - J-- L-J-J--L --I --I--L-J--I-- L-J--L.-L- !111111 1111111 50,0- - _T --,-_’ ~ -,--,--~-~--,-- ~ -,--,--r-~--,-- ~_T--,-_r-7--,- -T-7 48,0- - -L_ J-_ L- J_ J--L-l --I__L-J--I__L-J--l__ L- J--I-- J- I--I- _L - _I - --.--;__ } - + --:_ - ; - + -_;-- } - { _-:_- } - + __;-- } - + __;_- ; - + __:_- ; - + __,- 46,0- -: % 44,0 -‘-*--’--P-7--’--P-’--’--’-+--’--*-” --’--’-i--’--+-i--’--”-i--’--? 42,0- -, - J __I__ L-J_-l--L_J_-l--J_Jl-l-- L-J__l--L-J__l_-L-J__l_ -L-J__L-L-- 111111! 1111111 1111111 40,0- - _T__;-_’ ~-,--,--~-,--1--~-,‘ --l--r-,--l--r-,--,-- ~_7_-1--r_,--r--r-T - 28.0 +

Frequency, Hz

Figure25. Carpass-by at 3mwith engine switched off. The zero heightmicrophone is closer, 0,5mfrom nearest wheel. The strange effects atl,2,2and3 mat low frequencies maybewindinduced pass-bynoise. 25

Car paas by, engine on, 70 Ion/h, 3 m distance 94,0 a t I , I I I , 1 , I , t t I , I , I \ 1 92;0 -~--; -- l---+ --l--t--l--l-- + --I--I--+--I-- !---l --1--t-- -4--l--&--l--l- -Om - 90,0 1 --I--L-J--I--L-J--I-- 1- J--I--1--1--L-J--I-- L- J-_L-L-J__l_ 1111 I -9-0,4m - 88,0 ‘ --~--~-;--~--;-{--~--’ ~--,--;--;--:;_:-_--:-_‘ ‘ ;- 86,0 - ---*-+--,--+ -+--,--+-+__ *-+--,--*-+ --,--~- +--l--i---l--l-‘--’--r-’--’- +0,8m ~ .1_-1--L-J--J--J. --I--I---L-.-I--L- J--l--L- J--l--L___L_L II 84,0 - - - 82,0 ------; ; ‘--;--}-;--;--;-;--~--;--;--}--- -L- 80,0 -,--.,--; -,--~-7--T--T-T --r-T--l_-r-T -,- x 78,0 -.4--I--L- - I-.-L--I--I--4-J--I- -.$-4-- 78,0 :k-!--:-~-, -+-+-_:.--+_:-..-’-_+_ I_ h -A;: J--L-l._J_-L- ~--~ -,-y,:, -<--] -r_7-q--~-q L-+---I--I- * -1 --1--

52;0 --’””””””- +--l--l--+--l-- * -+--l--+--l-- l-- +--l--l--+--l-- i-- +--l--t-+-- 1- 50,0- -- L --I--L-J--I-- L -J--I--L-J-- I-- J-J--L-J--I-- L -J--1--L.-J-- l-- 48,0- - .- + --;-.-.;- + -_:-_+--: --:--. +-.-:-- :--+ --:.--fr -{--:--;- + --. :--}--: --:- 48,0- - _, _-,-- ~-,--,--~-~-- ,-- * - q--,-,--, --r-,--l--r- ~--,--r_n__r -T-=_ 44,0- - - A--l--l---l--l-- L- -I --I-.-J.--I--!--4--I-- L-.I.-_l-- l-- J_ -l-_ L --I--L-L--I-- L 42,0+!!!!!!!! !!!:::::!: ::!!!!! :lr.g~~g g.~gg~~ ggggggg ggggggg g . ..N 6* UYOMON Qs :’z$lggg z . ..- >?

Frequency, &

Fiwre 26. Pass-by by the same car as in figure 25 but with engine switched on. N.B. ‘ Tie zero height mi~rophone is closer, 0,5 mfrom nearest wheel. The strange effects at 1,2,2 and 3 mat low frequencies maybe wind induced pass-by noise.

In figure 27 a comparison is made between figure 25 and 26 for two heights. When the ,.- ,, difference between the curves is less than 3 dB tyre/road noise dominates and when it is ,. greater than 3 dB engine noise dominates. ‘.

82,0- , , 1 , 4 , , 1 i , 0 , I t t 1 , , a t i , # ______+--:-_ 80,0- --+--]-- ;-; --; -+--; --}-+ --;-- +--; --;-+--:- -- ‘ : : ; : : _J__L_L _J-_L_L__l__L _J_.J-_L-_:__:_J-. -L_J - _l--l-_ L_ J__l__L__l _- 78,0 ;- It 1111111 !111111 .111 76,0- -’ 4--1--t- -- I--4--I--I-- -1 --l--+--l-- - - l-- t--l-- 4 --l--4-l--l--+--l-- 1111 111111 74,0- --’ --:--; -1 -L-: --:--: --l--’ -v 4-- -,--,--f-<—-l- _-, -_ ~_q__,--*-+ -- 1111111 I 72,0- -“-’-_T _ ;_ :_’_-:_-.:-’- ‘ --, _r -+__:_ r--, ------r —,--,- _r_ 7-_ 70,0 ------‘ : : , , ‘ , -J ------: ; , : : ,--’ -+--, -7 ~:+--:-- +--:-- 88,0 :- -:-J- --:--L 1 88,0 - --l-- +-4-- -.+- - i---l--l-- 1 ,l__:_;::;:;::*m;-: -~-:::::!:;:: _,_ , _r_; -~ --1 -T_ q_- 84,0 Ir-l r-r-1--r

~ &’,o 1 1 - “-1--~-,--1- -1 ,--~--,- -om/Engin~~n ‘~- ‘-1 ‘~-1 ‘~-- i--!--

I~IIJ-&*+--~--Li--i--l- J- 80,0 lotiEnginedf ~~$~-~-j~_L-:lJ- % 58,0-1,,,,, ~_-l__l. _J__L_A..*.-A(l ,,1, -_l_l___ L--l.-,, +4rn/Engine on I 58,0 _+__,.-- +_+__~ _ + _ -,__ +_+-_,--- +_+- _+_.l__A:_+ _l__+_ ‘ _ 1111111 —x-4m/Engine off I I I I I 54,0 _, ‘ __;-_ T-7-- r- T--_r_ 7__;_;_- ;-;_ m -r- T-a--’r ;.- -_*_;_ 52,0’’” _,-. -l_ -r-,_-:-+-_:_- ;_; -_~__ + --;- _} -;-_:__: _; .--: _ + __:-- _}_,_.-,-\ +_ -:__ ---- 50,0 -,,,,,,,,1--I--L-J--L-1--I--L- J--I--L--I--L-J--)--;-,,, ,,, , : --:-.+--:--:-;--:-- ; 48,0 -, J-- 1-- L--I--L - J--l--l---l--l-- L--l -- L_.l --l-- L_ J_- L_.L _-l-- L_ -l_ _L - _- 1111111 Itlll[l l]llltl II 48,0 -+ --l--+ -+ --l--+ --l --l--+ --, --+--, -- l--+-- ,-- +-+-- +- +--,-_ +_+__*- \ _+- t 11111111 1111111 44,0’’’’” -T __,-- r-l-- r- T--: __; _l -_:__ ~ -7--r-T--l-- ~-T_-r-T-7_- ~-7_ -r-r_ 7_- -+__ :__ +__: __lr _ +__[__ :_ +__ :_ -+__{ __!r _ +_ .-[__ +__l __ lr_+__: .--}- +- .-:-- ;-. -,- 42,0 \ 40,0 -,,,,,,,,L-_l--L-J--l-.l --1--L-J--L-L- ,,, J--,,, L-J--L-L-J ,,, -- L-I--I--L-J--I--,, ,,, ,,, L--l -- “~ ‘ ,-

,~,

Frequency, Hz

Figure 27. A comparison between rolling noise and rolling+ engine noise. , -. .. —..—— ,~~ .. . .—

3.5 Integration time

LE as a function of integration time (or angle) is given by eq. (1.1). Theoretically the angular fimction 10 lg(Act!)= 5 dB, 4,4 dB and 4,0 dB for the three cases shown in figure 28 which gives experimental results. We can see that the agreement is good for the low frequencies where we can expect the source to be omnidirectional. The difference between SEL and SEL 5d is 1 dB and between SEL 5d and SEL 3d is 0,5 dB which corresponds to the theoretical differences. For the higher frequencies the agreement is a little worse. Because of the higher directivity of the high frequencies the contribution from far away is smaller and thus the differences between the cases decrease. The conclusion that we either have to measure at least along A 5d of the road or we have to correct the measured values theoretically.

98- I 1 I I s6------.- “+SEL - --- +SEL 3d 94- - A

92------

sO- -

------~.

%s6 ------

I e4------

82------

eO------

78 ------

76 * Zzs’:: : ;g~g ggggg Zg .-,-,- g --- Ncu Zv Frequency, Hz

Figure 28. Evaluation of sound exposure level using different integration intervals. Station car, 70 kdh, distance: 15 m, microphone height: 5 m.

3.6 Time history

3.6.1 Car

Figure 29 and 30 show the sound pressure level during pass-by as a function of the position of the car (Om corresponds to front of car crossing the normal to the direction of propagation through the microphone). The theoretical curve is the curve to be expected having two uncorrelated equally strong point sources located on each wheel axle. The rather flat curves at high frequencies indicate some directivity forwards and backwards (horn effect). The more complicated behaviour at low frequencies could possibly depend on interference between at least two correlated sources. Please observe that the microphone is on the ground, that is there are no nonstationary interference effects between the direct and the reflected wave . 27

Rolling, 70 km/h

75 m ;“ 70 +125 Hz $ 65 -R- 500 Hz -A- 1000 Hz ++ lBOO Hz

m r : 50

I 1 I ! ! I ! 1 I , , I ‘“ 45 # [ I -30-25-20-15-10 -5 0 5 10 15 20 25 30

Position, m

Figure 29. Pass-by at 5,65 m across asphalt pavement with microphone on the ground, 70 ludh, VW Passat Variant-98. Measured at Hasslosa 990519. Leqduring 0,17s.

Car, 70 km/h, cruising, 306

+125 Hz I 1<1 -1 J&L=I+P + 500 Hz + 1000 Hz + 1600 Hz

,s- ,.-. ,-

45 -30-25-20-15-10 -5 0 5 10 15 20 25 30 Position, m

Figure 30. Pass-by at 5,65 m across asphalt pavement with microphone on the ground, 70 km/h, VW Passat Variant-98, 5* gear. Measured at Hasslosa 990519. L.q during 0,17 s.

A possible explanation to the strange directivity at low frequencies is given in figure 31 which shows a theoretical simulation of two correlated point sources 2,5 m apart passing by. As the result is similar both with engine on and off such sources might be aerodynamic noise sources.

~...... z.— .-. .vr...... ,. .,,,, .?--,=. %k...... -.’ . . . -...... L. --- , ...... J,>.,.-...... — —.

-5 1 I I 1 I I ! 1 1 I 1 1 1 1 1 1 I 1 1 1 I I -10 ------: - _ --- .-- ;------r ------~______1 1 1 1 1 I 1 1 1 ! I I I I 1 1 I 1 m 1 1 1 1 1 u -15 . ------L------1------.---L ------L------I 1 1 I 1 I I I 1 IL ------:------L------20 1 ------1 1 1 1 -25 A------} -.------;__ -- ;- 1 1 1 1 1 I 1 1 1 I I 1 ! ~1 1 I 1 1 I 1 1 -30 ------~------*--- --i------l------*------1 1 I 1 I 1 I 1 1 1 1 1 1 [ 1 1 1 1 1 1 1 1 I 1 1 -35 , , -30 -20 -10 0 10 20 30 Position, m

Figure 31. Simulation oftwo equally strong pointsources 2,5 fromeach otherpassing 5,65 mfromthe microphone.

3.6.2 Truck

Figure 32 and 33 give the time history of a pass-by at 3 m and 10 m respectively.It is dil%cult to draw any firm conclusions. However, it seems to be clear that there is assymetry.

Truck passby (Volvo FH12 with 24 tons 3-axles single wheel trailer) at 30 Irm/h at 3 m distance and 1,2 m microphone hsight w. , a , i 11!11 11 11181 1 11111 I ---l ----l---t --- I----I ---4 ---1- ‘/-:--uA---:---:---~ ---:---l

---, - --, - -- f-- -~ ~-fl---~.

11111 ,r 1“ . ---4-”--4-- -+---l----l- -- 4---1---- IUi \ll , , , , , , , , } ,- ‘w:,’ )’, vi 1! 111 1111 “’-kw1? 1- J ---;---:----;-.--;-- -;---;---J.---1---L- --l---J---L-- n;;llllllVV. 1~~:~:: ‘1 “1”11 I Ill!! !!!!! I 40 29

Truck pasby (Volvo FH12 with 24 tcma3-exles single wheel trailer) at 30 kmlh at 10 m distance and 1,2 m microphone height 82 80 78 76 ~ 74 z. 72 ? 70 ; 68 : 66 ; 64 ; 62 ~ 60 ; 58 56 54 52 50 46 46 -,--,2--:~~~:--:----:---:-- i----, ---+------:+ ------:--J-:&__+--- --~u~~~~--- _. ,- - “~#,,1- 44 ---1-- --:--- L---:---- ;-- .-:--- :---L- -. _:--- J---: ----- . 1 1 1 42 L ---, --- -1--- + ---l----l --- +---+--- l----l ---+--- ● ---l---+--w r

Tid(lOms*n)

Figure 33. Time history of a pass-by at 10 m distance.

3.7 Ground attenuation .,- !.

3.7.1 Sound exposure level ‘.

Figure 34 illustrates the ground attenuation. It is obvious that low microphone positions cannot be used above grassland and similar “soft” surfaces.

Car pass-by,10 m aephal~ 5 m gta~ 80 krnlh 66,0 66,0 64,0 62,0 60,0 58,0 56,0 54,0 ~ 52,0 ~- 50,0 @ 46,0 46,0 44,0 42,0 40,0 28,0 36,0 34,0 32,0 gg~ g:~ g~jj %gg g~$~ gg Frequency, Hz

Figure 34. Propagation above 10 m dense asphalt and 5 m grassland. 4 different , -. receiver heights. .,.

-- —— 30

Car pass-by at 90 km/h, 10 m asphalt 72,0- , , , , , I , I # , 1 t # , , , I 8 I , I I a 70,0- --1 , , , , , , , , , , , , , , 11!1118 68,0- -

04,0- - 62,0- - -;-+ -; --: --:-- :--:-- ;-+- ;--;- -;-+ -1 * ecJ,o- - - L-I.-J--I.. :. 5a,o- - L- l-J--

-q-.., --,--p-F -7 , --r--,--,--l-- ~ - f - y-q-q--,- -1-

40,0 -!.-.!- -!--l-_ 1--1--1-- L- 1-l --1--1-- I--IL-!. -L-l--l --1--1-- I-- L-L -1--1

36,0 %’QZ s%~g?s:z:?zz~gs~g $Egi$ig z

Fraquency, Hz Figure 35. A-weighted frequency bandvalues. Propagation above dense asphalt only. 10 m distance and two different receiver heights. Please ignore low frequencies at 4 m!

. Figure 35-38 show propagation over 10 m mixed ground with different ratios asphalt/grassland. Propagation over dense asphalt only is shown in figure 35 which also shows that the background noise at low frequencies is significantly higher at 4 m than at 0,2 m. It also shows that the sound pressure level increases with height above 1000 Hz although the distance to the higher position is longer. There are two possible explanations for that. Either there is some ground attenuation even when propagating over the very dense asphalt only or the source has a higher directivity upwards. Another interesting result is that the two microphone positions yield identical results between 250 Hz and 800 Hz. This is an indication that the sound source is low. This is logical as we know that tyre/road noise dominates at this speed. #

Car paas-by at 90 km/h, 7,5 m asphalt and 2,5 m grassland 72,0- , , , 1 I I I i 1 , I , , , , I t t , k , , I 70,0. - 5a,o - - -;-+ --: --; --:-- :--;- +--: --: -- ;-- ;--+- 60,0------

60,0- - 1111 - r-,-<--,-- ,--

~- 56,0- -- L -l-J--l--l-- 1-111111 ~--,-- r-, _7_7 - -- r-T-. ~ 52.0- --:-; A_-l-_l--L-L-.l _ A 11111 [11 Ill + 50,0-

--- ;-- Ir -;- ;--: --; ----- :--+- +--;- -: --:-- ;-+- +-. +-- ;---

1111111 1111111 I 40,0,

30,0- -- r - ~--i-m--r ‘ r-r-7-7--l-- r-r-~-~-~--)--r- r -T-7-y--I--I-- r-r , I , I , , I I 9 , 1 I 34,0 -i I I ! ! I I 1 1 1 ! ! I 1 %--ZZZ zg~g:: ;g;;:g: g[~:ggzs G --- 3s g

Fraquency, Hz

Figure 36. A-weighted frequency band values. Propagation above 7,5 m asphalt/2,5 m grassland. 10 m distance and two different receiver heights. 31

Figure 36 indicates clearly a significant ground attenuation above 1000 Hz already with only 2,5 m grassland with a very low microphone position. Compared to figure 35 there seems to be no difference for the 4 m microphone position. -.

Car pa+y at 90 Ian/h, 5 m a~halt and 5 m gra~and 70,0- 1 I , 8 1 I , , , 1 1 , t , I ea,o - -- L_-l_J_ .1--L-L- L_-t _ -I --l--L-L- -t. L_-l--l__L_L. l- J-- 6s,0 - - - $ -;-; --:- _:-- ;- +_; _-:__:_-} _}_+_ 64,0- --;- - l -- l --l --l--l--+ --l--l--l--b-t- 4-4 _T_+ __: --: --:__ ;_;_ +_ -:__ :__ :__ ;_;_ 62.0- - lnul-i- &),o -+-~-y-+--~-p - +-q--j--,--p-+ -* +_+--,--+-*-* -<- --l--t-t-+- _L-J_J--l__l__ :-+_; __; __;_- j-- !. ------I I : I : ; ; ; -:-:-.:-:- Ill 111 _T_T_7--,--r- _T_7_ q--,-- ~_7_q_-l_- - r - ~ --r --l--,- -r-*-7- -L_J _ _-1-- l-_L _ J_-l- -L- _l_J _ _l- _J. -L--l __l_- -L-L-J- 111 11 11! -~--r , --:__ }_;_+-,_ -,--. r.-r.-, _l__:r_:--r - -.,__;__\_’_;-.;_ -*- -4--I-.-I--L-L- -1 --1--L-I.-J--I- -I-- I--L-L-J J --!--I--L L-.I-

-: +-4--’- - T-,-;--{--}-;-;-+--:--:-- ;-+-+__l 1--:__:_l-.;_ -+--t- -1--l-- k-+-+--l--l-- l-- +-+--l--l--l-- l-- +-+--l--l -+ -+-+ +- --- _; __:-- ;-. -.;.- +- +-_: --. :__ ;__+- +--; --: -_l-- \-+_ +__:-_ :------11 - ~\/1 111 .wo+z<+-- l--l-- l--l--t --t --l--l--i--t-i--i--l--l-- I--t--r-+--l--l-->-*-*\+ 40;0 L - 1 - J--I-- I-- L - 1 - 1-J--I--L -L-1-J-J--L-L-J.-1- J--L -L-L J._J- 111111 3S,0-+-’’’’’” 7 -7--l--r-T-T ‘7-7--I--r-r-“’’’’’” -r -7--I--r--r-T --r--I--r--r-r- -T- 33,0 - L-2_ J--l--L-L _l_ J -J--l--L_ L_l-J--l-_t-_L _L_J__l _-1--L- L_L _ - -: _;_;--;--:-_;_+_; __:__;__l ~_#_+_; __:__ {-_:_l 34,0 r T -+-4--:--:--}-;-T \]

Frequency, Hz

Figure 37. A-weighted frequency bandvdues. Ropagation above 5masphalti5m grassland. 10mdistance andtwodifferent receiver heights.

Figure 37 confw the result of figure 37 as do figure 38 below..

Grpasbyat 90 kmlh, 7,5 m as#halt and %5 m graaSand qo - 1 1 1 I 1 I I 1 , , I i 1 , , 70,0. - - +-+--l--l--l--l-- +-+-+--l--l--l--l- -1--+ --l--l--l--l--+- ● +--i--

.,> 64,0- - - 1.-~-~-~--,--,-- ~-~-T-.r_q__l__r _r .,.. .. 62,0------m 5&o- - - ~-~-,-,--1--,-- ~-r-T-,-T__,_ ~ -~-j--’,-,-,--,---,__ ~ ~_ T_ T_,__ - +-+--l--i--l--l-- l--+-+--l--l-

11111 S 5Q,o- .c - - r --r --l--, --l-- r--r--T _T s 4a,o- - -$.-.4-I--I--I--I- -!--l-- .!. --t- $46,0- -- f.-+ ____ I__ L_ L_l_l_J__I__l__L - L - 1 -:-J----- d 44,0- - _T _ ~ _}_+_;.-;__;__:__ }_; _+_, _;__; __l__ 42,0- -

______26,0 I ‘ T-T-l-l--t--l-- 24,0- - 22,0- -,,_L_l-J_ ,,, J__l__l-_L-L_L,,, ,,,_J_J_-J--L ,,, _ L_ L_l_d_J,,, ,,,_-l_ -l__ L_L,,, _ L_4_ ,, ? “03:ss38g$~g3:5~33 g:~g~gggggg .. N’N C-l *o

Fraquency, Hz

Figure 38. A-weighted frequency bandvalues. Propagation above 2,5masphalti7,5m grassland. 10 m distance and two different receiver heights. Measured after the lunch break.

Figure 35-38 have been compared with calculations using the coming Nordic prediction method forenvironmental noise, [10]. Thesound power of thevehicle has been distributed to 3, 0,01; 0,15 and 0,3 m, and 1 omnidirectional point source, 0,01 m, respectively. The flow resistivity has been assumed to be 20000 krayls for the road surface and 100 kRayls for the ground surface. The impedances were measured according to NT ACOU 104, [11]. The results are shown in figure 39 and 40. . .

, ...

., - . -.—m- ., ,:----- . ,...? ---- ,. . . ..=--...... ,. ,., . —.——. :.

‘hs=O.01,0.15,0.320000/100kRavls. 20,0

-5,0 Inoloorooolnoo Ou’)oooooooo 0000000 CQCIWU)WWONUI Olin. oacoooul Ooo1oooooo ,-.-QNCNJWJW mmmo~mo m.-OOO-JOO l-1-. @JoJ co* Inwa Jo

Frequency, Hz

Figure 39. Calculated differences between SEL at 4 m and 0,2 m respectively.

The results of figure 39 and 40 can be compared with the measurement results reported in figure 35-38. Bearing in mind that we study the very extreme case with the receiver at 0,2 m and an impedance jump the agreement is not too bad. By introducing vertical and horizontal directivity the values at high frequencies will increase 1-2 dB and the agreement will become even better. Actually the worst result seems to occur at the seemingly easiest case, that is propagation over asphalt only. By limiting the sources to one only at 0,01 m we can improve this case a little, see figure 40. However, for the other cases there is no improvement. The general shapes of the curves seem to be better using three sources at different heights.

hs=O.01 20000/100 kRayls 20,0 —

15,0- — —

E m. o 10,0 -— — -! Ill a

f 5,0- — — w u)

0,0- ~ ~

-5,0- ~ U)cuoocoo,olnooo !430000000000 00000 ‘*-”” ”:2S8R3SS%S88888 288888 t-t-l- cucumwul cocoa

Frequency, Hz

Figure 40. Calculated differences between SEL at 4 m and 0,2 m respectively. >

75.0 , , , I 1 n , , 1 , I , , , , , , , , # # , t ,

70.0

65.0

~ 60.0 ~=~+;~d’~~~’~~;;--r7-~~:!:T:;-n:;-#;-;-l-;-;-l-:%-l-;-;-!- m 1!1 III 111111111 !1 u Ill I 11111111 11!1 -,-,- J- 55.0 ,-+-r -, r-t-7 -r-r 7-r-l-7 -T .l -T-J- w 1111 _;&--$3\,:,~:;;;;;:;;;: :::: m Ill l?; 50.0 -- -1--1 -t -l--l-+-l--l-+-t -1- +-t-l-+-t-l-+ -i--l--i +-1- 111111111 1111111111 11 %!.! 1111!1111 !! 11111111 1111 45.0 J L-l-J-L-l-A-L-l_ J- L-!-A-L-I-J-L -I- J-L-I-J-L \- ~ 1111111/ 1111 !111 1111111 14 1//1/1 I 1 1 1 1 1 1 1 II 1 Ill 1 11 1 1 1 1 1 INI 40,0 r

35.0

Frequency, Hz

Figure 41. A-weighted frequency band values. 4 different measurements at 4 m microphone height.

,,.-. Figure 41 shows that the 4 m value is essentially the same for all configurations at and above 250 Hz. However, if we don’t accept errors greater than 1 dB we have to exclude :, at least the 7,5 m grass case although the slightly higher values around 1000 Hz for 2,5 m asphalt/7,5 m grassland may depend on changed conditions. The measurement took place a few hours after the other measurements.

3.7.2 Maximum sound pressure level

In figure 42-45 the maximum sound pressure level during pass-by using time-weighting F is shown for some different cases. The spread in data is confusing at low frequencies. As before a possible explanation is wind induced pass-by noise and background noise. Comparing figure 42 with figure 35 indicates that the directivity at high frequencies is significantly less for the maximum level than it is for the SEL level. The explanation is that the horn effect is not as efficient perpendicular to the direction of propagation.

Car pasby ●t 90 Iunfh, 10 m asphalt 70.0- , , n i , # 1 I , , , I , r , 68,0. - -I--I--I-4-4-+- + -I--I--I--I--!-4 -+-k -1-+--i-+-+-i- -+ -l-- moo- - 64,0- -::::;:;;: ;’ &20 -- 60,0. - -b-l--l--l-+-+-l- - I--I--I--I--!-4 l-l._L_L_L- ‘ \-

--j --t - r - l-- l--,--,- q-n_7 ~_ r-~-,-- ,, % 520------+_ +_: -:_ -;_-; --:-.:- +_+ Ii s 4.9,0-- s? _l-l_J. _L_L_l__l _ _l-J-.L -L_ L_!-- l__l _ J_ J_ l-L-L- .. .to,o -- -,-~-~-~-*-~-~ -,--, -~-,-,-~-r - r-l--l-T-,-T-r -r -r-, I-- I-4--I--I-+-L -I--I--I-4--I-4- t - !-- > -l--l -+--l -+-+-l--!--l- .,. -l__l__l_J_J-l_L_L -l-_l_J_ J_ J- L- L-l- _l__l _ J_-l_L_L_L_L -L-

Frequency, Hz

Figure 42. A-weighted frequency band values. Propagation above dense asphalt only. 10 m distance and two different receiver heights. :.. -. __, —.. —....’. . . .

CarpasLyat SW 7,5 m aqimlt and &5 m gmsdand

j 44,0 !t?O’dt--- ‘l-l-T-~-~-~-~-,--,-i’’’”” “’’’’’’’’”,-,-~-~-r-i-~--~--”- ‘kqi t ● 430. --l --l--i --i-+-+-l-- hi_;__;_;-;-;-;-:-%-I--I--L::::+:+\ ~ -: --;--: -; -.+ -+. -: -. :--;__ ;__;__~ -+-+ -+-: -Ir-:--. :-. +.-{ -;_l _; {

3s0 -- ~-l--, -T- T-.f - ~-r-r-r-,--l- ~-~-,-r-r..r -,--, --I-T-7-T \ -T- --I--J - 4 - + - I-- I-- I--I--I --I- ~-~-+-~-~-l--l--+-J--J- +-+- [ 320+!!!!!!!!! !!!!!!!!!!! !!!!!

. Freqwwy, R? Figure 43. A-weighted frequency bandvalues. Propagation above 7,5mdense asphalt and 2,5 m grassland, two different receiver heights.

Car pass.byat 90 bW1’$5 m a@alt and 5 m grasiand Xlo , , , , , , , I , , I 8 I , i 1 1 I , , I 630 -1--l--J -J- L- L_L_L -L_t__l_J_J_l_L - -L-I-J--J-J-.I- L-L-L- E6,0 -~‘ -,--l-3-,-T-T‘ ‘ ‘ ‘ ‘ ‘ -r-r1 ‘ -,--,‘ ‘ _T ‘ -,-T‘ ‘ -r ‘ ;--’--l:; ,2; :l,\; -l--\

64,0 -L -I--I-J-J-L -L_ L- L-l__l_J --1-1- -L -L-- -- 1--1 -L-; I +-4m -r -,- -’- -}-: E20” , ;.-; -+_; _;_: -[-_:_ ;- +-; r-1 r-r-r-tI I I T-7I a. MO _l--l-J--l_J_L - L - L - L .-I--I--! -J- -L-L-L-I--I- - A-J-L-L-L-, 11111111 11111111 A 11111111 Ii ------~-r- -r---- -,-r-r-r- MS3.0, 1;”” , , -, - T - T - r-r-,--l_ ,- I -1- ;. 56,0 _LJ-J_J--l_L_L_L -L-l--l- -J- -I- J-J-J J-L-L-L- / -x+ 11111111 1 g54,0 -:--: -;-;-;-;-;-;-;-- -’ ‘ ‘ ~ 52,0 1_F-:_-:_.&_:_:* g+-:-:--fi-j-’.m q 46,0+ -,--1-)$- ~-fi

1111 7 7 T r r-r-r-l-7-7-T-r-r- r-l--I--t-7--r- y:~; n:yp”-”’”- J-A-J-A-L-L-L-”-” -1- J-. -A- L-.L -I.-L- L -l--l-A-A-A-& L L , ;M--,--, --- , i -T-~-~-l--;--l--l-~-T -T-r -l--,- _l__l- T-7-T_ ~ ~-

L-,--,--J-4-4- L-L-L-I--I-J- J-1-L-L-L-I-J- J-J-J-J.-L- -!

Frequency, Hz

Figure 44. A-weighted frequency band values. Propagation above 5,0 m dense asphalt and 5,0 m grassland, two different receiver heights. 35

CarpasAy at 90 Ian/h, 2,5 m asphalt and 7,5 m grasdand 72,0- 1 I I , n # 1 1 1 i I # i I # 70,0- --: -: -:--p -l-- L - J- J - l--l-- l--- 6a,o - -,,,,;’------,--:_; --: -_:-_ :_-lr -- r_{ _-: --:-- l__l_-L - m,o - -- *-*--I--I--I--F-+ -+--l--l--1--F-+-+- 64,0- --, 1-J-J-J--L-L-L-J-, , , , , J_-1--L-L 1111 62,0- - -~-,-,-~--,--r -;-;- ~_-,__,--r-;- ,_T--,_-l--r-T- m lxl,o - - -&-L--t--l--l-- L-L.-.$--I-A--I-- L-I. .l-4-4_-1-_l-- &_ --I--I--I--I--L -- ‘n;. 58,0- ~’ - ~ - + --: --:--;-- :-- + _ + --; --;--:-_ Ir - - + - + -_:-- :_- :-,- } _ + - 56,0 -t-+-+--l--l--l--+-+ -+- -1-- -+-+--i- --l--l--l--+--l -l--l--l--t- L%,o2 -, L_L-J-_I-_l--L-L-J- -1 -!- -L. - 1- --l- I--L-L--l-J_ l__l--L-L- g52,0 -r-;-;--;--:--:-;-;- -,--;--}-;-T-;-.-:--, -\-:-;-;-_l -:--}-;- =Q60,0 -b-~-~-~- --- -~--1--1--~-~-~- J-d--l-- -~-~-~--t-- -~-~- ~48,0 - --; ------: ; : -1--- ___-l --f-_f-- IL- !. -1 - J -_f--f-- IL- .! --l --l__l- -- L - 946,0 -r-T-,- --’ -~-~-,-q--,--‘ ‘ ‘ ‘ ,--,p-r-T-,-q‘ ‘ ‘ ‘ ‘ ‘ --l--r-r-T-‘ ‘ ‘ ‘-&;--’-;- ~ 44,0 - L-1- - --l--L-L_J_J--!-_I__ L-L-1-J-J--I--L-L- 1--!- l__l__L_ _ 42,o -r_‘ ‘ l--;--;--;-;;;-;--;--;- -;-;-;-;--;--;--:-; _+-;_-.,_ I__\-r 40,0 -+ - -1 - -1--l--+ - + - 4 - -1--l--l-- & - + - + - -1 - +--1--> - 1- - + - -i Y--1--1- !- - t - 28,0 - ’ -+-:--:--:--:-+-+-+--;--;--;-+-,+ -+--;--;--:-;-+-+--:--:--l -+- 26,0 1/\r--r--l--r--l-- I--T-7--I--I-- l--r-r--t--l-l --,--l--l---?--l --,--,--1-- - i

Frnquency, Hz

Figure 45. A-weighted frequency bandvalues. Propagation above 2,5mdense asphalt and 7,5m grassland, two different receiver heights.

In figure 46 the geometry of figure 45 has been used to calculate the theoretical difference between the two heights using the same method as the reported earlier for the SEL-level. The agreement is very good in this case. Notable is the fact that the source position seems to be very low at high frequencies and at low frequencies the location of the source is not very critical.

,-,<’. 2,5m/7,5m 20000/100 kRayls 4 . . 16,0 !:. ” 14,0

12,0 %. ~- 10,0

=- 8,0 ?$ E 6,0

0,0

-2,0

Frequency, Hz

Figure 46. Theoretical calculation of figure 45 with different point source configurations.

Figure 47 shows the time-weighted F time-history for selected 1/3 octave bands during pass-by by a passenger carat 7,5 m and 70 km/h. The microphone was on the ground in order to avoid uncontrolled interference effects at low frequencies. We can see that the A-weighted level has a broad maximum during about 0,6s, a time during which the 63 I% value may vary about 10 dB. In figure 46 the difference between the true maximum and the maximum when the A-weighted value has its maximum is shown.

,.-,

.. .. -17--,m.-..-.?.. ,.. ._. ,,:,.,. .. ---- ...... - - , . --- & ,- .’,-., ,. .-———— — —- ——. ——— — ————..——

Pass-by at 7,5 m and 70 km/h

75,0 I I I I I I

I I

I k 70,0 7’ I I f I xl I I —31.5 65,0 — 63 . . . . . 125 m -0 60,0 — 250 . . . . - “500 55,0 — 1000 —2000 50,0 —4000 ,, , — A-weighted 45,0 h’

40,0 3 4 5 6 Time, s (1 s= 19,4 m)

Figure 47. Time-history during pass-by of a passenger car.

9,0 \ 8,0 < +7,5 m, mean

7,0 ~15 m, mean \————— R 6,0

5,0

4,0

3,0

2,0

1,0

0,0 U-Jm-oocooou)o Oomoooooo 000000000 04 WU3acoomlmoul .Oo moo moo O1oooooo --- CN OJ m w u-la co o ml w o In? o 0 co o 0 z . . . m N mm’ mm coo

Frequency, Hz

Figure 48.Difference between truemaximum (LPF~x)andmaximum atthetimeof maximum A-weighted level.

3.8 Aerodynamic noise

By chance we happened-- to measure one day with strong winds exactly parallel with ~he road. The result is shown in figure 49. We can see that the low frequency sound pressure levels are considerably lower in the downwind case. As the high frequency tyre noise is 37

the same the results indicate that aerodynamic noise may be the difference unless the extra load on the engine makes the difference.

Reference 2: Gear 5/2500 rmp (100 km/h), Wind: around 8 m/s

95 1 I I 1 I i I I 1 1 I I I I I I I i I I 1 1 I 1 I II 111111 Ill 111111 11111111 11111111 111111111 11111111 111 1 II It Ill 90 . -.--L---J-- -l- J..I -I-l 11 111!1 i 11 11 11111 11 11 11111 11----- +- _.-:__ _,1!----- 111 85 11 !111 II t 11111 II 11 11111 11 11111 80 l-l---”--+ --1-- -I-+-l-l+ 11 II 11111 s 11 11 11111 g 11 11! 111 111111 11 11 11111 -: _-:__: -.:+++ +_____ ;--.-.;_ +_ }.-:.. :- I-l----- J__ -!-~~1~ g 75 11 1 \- 11111 :,. . !1 111111 111111 11 !11!1 . . ;\ ,. 3 11111111 111111 11 1! 111 II 111111 111111 \II 11- 11111 70 q --,- q - ~ *, * * -----,--- p- +-r-,-~ p,---- _,----- l- l-i-l-l 11 111111 11! 111 11 11 1111 11 1 [1111 111111 11 11 111! 11 111111 111111111 11 !1! J--l_-l-~~JJ~---__l-_- ~_J-LJ_l_l_l-l----- J---l -_ IJ 65 11111111 Ill! 11111 II -1-11 1 11111111 1 11111111 111 Ill 111 \ 1111 60 .-I- T1l+ l!tll18111 11111 55 25 50 102 250 500 103 2000 4000 104 Frequency (Hz) hrl =0.2m, T= 1.3

Figure 49. Difference in sound exposure level between up and downwind. The wind speed was about 13 mls. (Not 8 rnls as indicated on top of the figure). — —

4 Some measurements with parabola

In order to find out whether or not the sound radiation is about the same for all wheels some measurements using a parabola antenna were carried out. The measurement distance was about 10 m and the parabola which is highly directive above about 800 Hz was directed towards the wheelhoad interface. Some of the results are shown in the following figures.

The conclusion of the measurements are that all wheels radiate about the same sound power although there are large statistical variations. There is no strong indication that the driving wheels make more noise than the other wheels when the vehicle is cruising at constant speed.

lD19JOng container truck

58s0

93s9

S4sa

9293

9303

C-WI

g M.cO

: 82.CU m woo

7803

7003

74.nO

T2.co

70.M

Figure 50. Truck with 5 axles of the type shown in figure 51. .“. ..

Figure 51. Truck with 5 axles Figure 52. Truck with 5 axles

-’

Figure 53. Bus with 3 axles

000821_i~_bwk(MJJ)

02,ca , I

. Y ea,oo I A \ / 8s,20 PA\./i f\ A IJ YY Et4,m f I \ d Y k-’ d 8200. AA Al \ M,C17- Al \l”v ‘

78,M \A v{ a

\/ 74,C0 72.M -. IOI-. := u)):z~:: g~z~~$;gq~?jI T [1/S3S) .0.5 m Figure 54. Truck with 1 + 1+3 axles, 81 Ian/h

.— .-.—-- .. ... ~ —.- ~—— —. ,. . .— . ,

000821-1 91_truck(90-2)

Kc?@ +1 k.w. /} I

Figure 55. 1 + 2 + 3 wheels, 90 knih

000821-55-car(100.0)

lm.m.

/ 6.3,c0 * A.v@W 94,03 /~1 fll

\ / \ 70.02 mm \/ \ k

70.m 4 I 1234567891011 !213! 41516171819202122 232425262726 Z92JJ T [1154S) Bask Figure 56. Passenger car, 100 Ian/h.

000821-88-car(l 16JJ)

tm.m. ~ -

S6.co / / \\ 94.03.

\/ 52.03-

/ 60.02. I \\ s ~ 2S,CU % ~m i \w. I

12345675 91011121314151S 1718192cI T(I15Os) +0s m Figure 57. Passenger car at 116 lcdh 41

5 Some further measurements

5.1 Measurement site

All measurements reported in this chapter were carried out along a motorway. The measurement site was a checkpoint to test the weight of heavy vehicles. There was a 2 m high earthberm along the motorway. The unscreened measurements took place in a 15 m gap in this berm just in front of the bermfront.

!,. . 5.2 High exhaust 1-

Normally it is not possible to distinguish between exhaust and engine noise by using simple pass-by measurements. However, there is one exception and that is when the exhaust is on top of the vehicle. Figure 58 and 59 indicate that there is a qualitative agreement between predicted and measured behaviour.

Viared Konlrollplats, 2000-08.08, at the opening 100, e 1 1111111 11 I 111111 11 111111 95 1; -I-;;;%:---+--:-;-: ;;}:----;--:-;-::;: I II Illlhll 1 11111111 11 I 1 11111 9rJ -----11111 -;-}+ ++l+\; :---- +--; -’-_J;1111111 L:_-- _-;--:_ 111!1 I 1111111 11 11111 _l_~JJ~l_l__ -_~-_l- -l_~l_r_l 11111 11111 80 - -l_ LLl_l 11111 I 111111 11111 -. LLLLI 1 1111111 11 1111111 11111 11111 -- r-r-l-l I !1111!1 11 1111111 11111 !1111 65 -;-l; ;;-l; l---- ;--;; ;;; ;;; ,;----; --,- -rrrrl 1 1111111 11 1! 11111 11 11111 1111 60 -}-\; -l; ;+:---- +--:-:-;;;::--_-;--;- -t i t-i 0 hrl=O.2 m l[lll’’ 111’ Ill __~--l-_l_~JJ~l-l-__- ~--r_ .l-~~ 55 — hr2.1.75 m ,,, ,,, ,,, ,, 1111~ — hr3.4 m 11111111111 !! 111

250 500 ,.3 2000 ~ )0 104 Freq. (Hz) 10 m asphalt 85 kmlh u=2T3d = 2.56s) 5+(1) asles Figure 58. High exhaust. Measured values. J

Calculated pass-by at 10m from source at 3,5m height 95 r Ill lUtllthr=O,O1ll 11111 u u y_o-~_&r-l I Ill 11111111 ---- , ~~~ ~,-----, ---,--,- ~-,-,-,~ t..rllllll~mili 1111111111

II IAIIII1ll III 111111111

11111 111 111111 1!111!11 11111 88 7-17 TI-----; --:- ;-:-:: ;:-----:---;--:-;-;-;-;; ‘111111 111 111111 11111111

11111111111111111111111 -_--~--_~_l_~~~~~ l_l--_--l_ l_ll-J-l-l_l_l-l 661++++: , , , 111111 1!! 11111 11111 111111111 11111111 , , 85 ! , , t , , , , , ! t 1 , , , , 102 103 104 Frequency, Hz ,. Figure 59. Simulation of pass-by by a 3,5 m high source...... -. . l.r_..-_.. . .. —’

5.3 Screening of engine noise

In 3.2 some measurements were reported from measurements on an airfield. Below some additional results are reported from measurements on freely flowing motorway trucks. Figure 60 seems to have the same behaviour as figure 58 which indicates that also this truck has a high exhaust. Both figures indicate clearly that the high microphone position gives lower levels at low frequencies. This supports the hypothesis that engine noise is screened at high positions.

Viared Kontrollplats, 2000-08-08, at the opening I , r 90 .l-J-LJ JAJL----L--L-L-L JJJLL---- L-- LLAJ1LAJ1. 11111111 111111111 11111111 # 11111181 111111111 111111!1 11111! 1 85 _;-l-:; JJJ ;----:- - -L JJJJ L-.---:--L-: -~;:;:- 11111111 11811111 /,’’’’” 11111111 Pi 111118 11181111 ‘v’’’” ‘ ‘ ‘ 11111 8 -.+ ++----+--+- +- ++ +-4+ 111 11111 Ill 1!1 11111 111111 Ill 11111 1 7 --t- 114+ t--t--t- ti-lt- 1111 111 1111 Z ~ 1111 11 1111 1111 11 1111 ~7 --1- -1 -i-l-l ---- -r-T- T_tlT- co 1111 111 1111 i\ 1111 Ill 11!1 !111 1111 65 -;-;-;;;;;;----+--;-+- 7-111 T_17T 11111111 Ill 1111 1111 !1 111111 Ill 1111 11 1111 1111 ---- ~71T1111 - 60 -;-;-~J-’-’+~----+--;-+-111111 111! 11111111 111111111 111111111 111! --- hrl.O.2 m 55 - -- l-_ L- J- LJJJJ L---- -0- hr2=l .75 m “’’1’’’’’” ‘“ 111111111 + ht3=4 m 111111111 1111118 t t , , , , , , , I I I , , , , I 9 , 50 25 50 ,02 250 500 ,.3 2000 4000 104 Freq. (Hz) 10 m asphalt 74 km/h ~=2*T3d = 2.92 s) 4+(1) axles Figure 60. Screening of truck engine

Viared Kontrollplats, 2000-08-08, at the opening 85

~ 70

~ 11111 -1 1111! w 03 65 )! 11111 11111 1111111 11111 11181 Ill 11111111 Go :-;-:;;;: ----L--L-L-I- L l-u-----l---l--l- -1 -1-1-1 !1 11111 11111 111 1111111 1111111 11111 Ill 1111111 11111111 1111! Ill 11111! \ !1111111 111111 55 - --- hrl. O.2 m ---~--~-~,-rr ~ l-, -----,.--, --,- ~,_, -e- ht2=l .75 m ‘;’’’’’’’”; ““ 111111 111118 P + hr3=4 m 11111 !111 11! 11111, , , # ! ! ) 50 , , 1 25 50 ,02 250 500 ,03 2000 4000 104 Freq. (Hz) 10 m asphalt 68 km/h (l=2”T3d = 2.46s) 5 axles Figure 61. Screening of truck engine Figure 62 shows the corresponding results for a passenger car. Also here we have a clear indication that the low frequency sound pressure level decreases with the height of the receiver.

Viared Kontrollplats, 2000-08-08, at the openning 80 II 111111 11111111 11111111 11 111111 1! 111111 11111111 11 111111 1111111 111 !1111 11 111111 111 111!1 A 11111111 -L-l-LIJ-ll- 11111!1 it 11111 1 II Ill 11111 Ill Illti 111! 11111111 !11 11111 111! 1111 11111 70 +-; -: 1111 T----T--T ‘T -rll TT -- 111 11111 1111111 111 1111 1111111 II g~;’ 11 111111 265 :- J.- J.-L_LLJ-l*- 11 1111 W u)”; F 1111 ~ [[:::::: 11111 111111 11111 l!ll! 1111 -+’’.-LJ!!-+!----+-- + -+-;::.!++-.---.+-- +! 60 1! 1111 L11 111111 Ill 111111 11 11 111111 111111111 Ill II 111111 1 11 111111 111 L II Illltl 111 1111!1 1111 55 --~---r--r-l--i-i, ,y----~--~-T- ~, I +- nrl=..,0.2m , , , 111111 1111111 11-n_hr9=l.T5~ I I 1111111 1 I 111! I 111 111111 111111 .oE&smn,,,,,,,,,Ill 1!!!11 ,,,,,)jIll 11111 , -25 50 102 250 500 103 2000 4000 104 Freq. (Hz) 10 m asphalt 108 km/h (T=2*T3d = 2s) Figure 62. Screening of car engine.

5.4 Measurements with a barrier

As the measurement site used in 4.3 happened to have a barrier with a height of 1,75 m some measurements were made to see whether barrier measurements could be used to find out the positions of the equivalent point sources. Unfortunately the barrier had a low protection fence in front of it and together with a grass covered barrier top it turned out to be difficult to use the data. The fence obviously affected the high frequency measurements considerably .Nevertheless some of the measurement results are reported in the following 4 figures. The position hr= 1,75 m refers to a reference measurement on the same vehicle but before the barrier starts. The height corresponds to that of the barrier.

Viared Kontrollplals, 2000-08-08, barrier (hr6 is at the line of sight) 1 I 1 I i , , , , 0 , , , 0 0 , 1 , , 1 1 1 I ( 11 111111 11111111 11 111111 11111111.. /’%” [ \ :[[\\\ 11 111111 1!1 111:111> 11,4111~ 75 {-j-~jj~j~----+--+- ~-r~m77r--.+-~--~-~-~ +~j~ 11111111 Ill 1//-!!11 y;;;;;:;; \ \\;;’’’’” 70 --*,--T’-+-:-+;{+ ,x, ,,, ,,, ,\ s ,>: ::::;: : 65 u W

60 11111 ml-al l’\lllll

------1 ~> hr7=3.3 m ~;:; ;::::; -Y- hr2=l .75 m Itlltllll m111 11111’ , a , I , 50 , , 25 50 102 250 500 10’ 2000 4000 1o“ Freq. (Hz) 10 m asphalt 108 kmlh (T=2”T3d = 2 s) Figure 63. Measurements on a passenger carat different heights behind the barrier. -—,

Viared KcmtrcJp4ata, 2flWB03 ,bdnfer(ls6 iaatthelirwofsi@t)

~ JL_-_:_-+_l_Li !.lJL___;_;-~JJJ~i \-l-1111111LL1-l 1111111 181111 I 111111111 11111 !4111 1,, ,, 1 Illlllllkl ,,, ,,, ,,, , ,,, , ;;;;; 11111 777r8- 11111 81111 11111 11111 +++1-1- 11111 11111 11111 11111 ,J J L L1. 1111 II!

25 50 ,.2 250 SX11032C IYJ4C?33104

~uFtsq, (Hz) 10m@talt 74 knvh(E?T?d. 2.92s) 4+(1) axlaa “- Figure 64. Measurements on a truck at different heights behind the barrier.

Viared Kontrollplals, 2000-08-08, banier (74 ktih, 4+(I ) axIes)

-- +-+-+ + -, ++-,---- ,-- *-,-++ *I+.

-:~ 25 r------;--; -; -’-’-’~ ~’----~--}-~-}::~; E, 11111141111 Itlil 11 ;ii;li’ =, 1111111111! 11111111 ,, ,’, ~20 L- I- LLLIJ L--- L- J-* J-I JILI-— ——I— — L—I—L. J, II -1!1 1111111111 111111

ml0.

. Freq. (Hz) hr2 (raferance)=l.75 m & hr8 ia al the fine of sight Figure 65. Measurements on a truck at different heights behind the barrier. Sound pressure levels relative the unscreened reference position with sign changed.

Viared Kontrolfpfats, 200Q.08-08, Carl 00, 108 kmlh 25 11111111111

--*-- l-i-l-,- l* F, ----l-- e-,-p+~j+ Ill 11[ ----111 111 111 i I: 1 [11111118 Ill 111 1111 [111 Ill II! .= -1- L I. l-u. Ill 111 n. !11 111 In 11111111 111 111 ==-- l---T lTllTr, r,----,-- ~ -r~ rm- F Ki!lll, ,111 l,, ,, & 111 r 11- T1lYI III 1 1 1! 11111111 % Ill n. (n I LLLLIL ---J-J -1 J_l JILl__ --l-- L_l_ LIJ. Ot: -1-l 11111 1111111111 1 ,% *1 1111! 1111 111111111 ;;~p 1111111111 1111,1 -5 F -I- I- I- I- I-I I----*--- ++-, -4+ M---- ;--:-,- *+*, 111111!11 111181111 181111 11 111111111 11! 1111111 11111Y l-l-! LI-I-IL ---L --1-1 _l_l_ll Ll__-- I-- !-_ l_LLL l_l -10 ! , , , ,, , , , , t , I ! I , , t , t 2 50 250 5W 2LM0 4000 102 103 104 Freq. (Hz) hr2 (referance)=l .75 m & hffi i3 at the tineof sight Figure 66. As figure 65 but on a passenger car. 45

5.5 More examples at another test site

Figure 66 shows another test site. The width of the road to the fws grass was 2,6 m, the ditch was 6,1 m wide with its deepest point 0,7 m below the level of the road surface. The flat grassland was 0,2 m below the road surface and the microphones were 9,75 m from the ditch that is 18,45 m from the,nearest wlieels. The ground imped~ce was measured and it turned out to be quite soft,rthe flow resistivity was 160,kRayls. The !,.. . ~. calculations were carried out according to the latest Nerd 2000 method using two 1. ~. different source models. One used three source heights: 0,01; 0,15 and 0,30 m, and the ‘t.

Figure 67. Test site. The truck is in its right path.

A typical registration of a pass-by is shown id figure 68. The upper curve is a reference close to the road while the three come from microphones in the stand farthest away from the road. In the following we will only look at the difference between 4 m and 0,5 m.

Volvo Bori%, 2000-09-05, 2.6 m asphalt + 15.65 m grassfield with ditch 80 1 I I 1 1 1 I 1 1 I I I I I [ 1 I 1 I 1 I 1 I 1 1 I 1*.11111 !11 1111! 1,111 11111 11 Iyllll 111111111 lltllltl t ,5 ;--: :’’i::;: \ : ;“’’” ; : ::::: / ------~-r-L.LJ Jl !____ ~-_-l-._;_ ; -,-,-,-,- 1- 111 111111, Ill ,111 111111111 11111111 1111!11 111 !11111 1111! 111 111 111111 I-I-----1---L-L-I-I. -I-IL 70 -:-:j::-1~,:: I I I I ; ; #\----:--:--l-Wl- ‘?! ,., ,,, , 1111‘ 11111111

‘;5 50 102 250 500 103 2000 4000 104 Freq. (Hz) car023, near track Figure 68. A typical pass-by registration. ._ — .—— ., /... ._ ”.”

m v .

g. 10 0 J % 45

d u.! u) o

-5 U)oaoomooloooo Lnoooooooooo 00000 OJm=rmfocoomlmoln I-00C900UIOOOUY 00000 7 77 ol am w Uy w co o a Wo m 1- 0 0 m o 0 -1-l-mJt3Jm*ln mmo

Frequency, l-lz

Figure 69. Measured differences between 4 m and 0,5 m for 6 different passbys.

Figure 69 shows measured differences for 6 pass-bys. It indicates very little difference between the passenger cars and the trucks. The only exception is between 1000-4000 Hz where the difference is smaller for the trucks. In figure 70 a comparison is made with different source models. The agreement is rather good between the 3-source model and the passenger cars. However, it is rather bad for trucks around 2000 Hz.

20,0

15,0

E m o- 10,0 J w u) . :

: 5,0 4 w : to \ 0,0

-5,0 U)cuoomoolnooo In Oooooooooo 00000 Olmwu)coao(uu)oul l-oo@loomooouJ 00000 rt-. oJoJc9*uy facoooJ@omP Oo(r’joo .e. oJoJlxJw u-j @mo 1- FrequencyjHz

Figure 70. Measured and calculated values from 3 car/truck pass-bys at the test site shown on figure 67. 47

20,0

15,0- – m -a . ~. 10,0 -– : w v) ; 5,0- – - 4 Ill u) 0,01 ~ . ,, t’.

-5,0- r

Frequency,l+z

Figure 71. Measured and calculated values from 3 truck pass-bys at the test site shown on figure 67.

Infigure71 different sourcemodelsarecompared with3truckpass-bys. Upto2000Hz theagreementis verygoodwitha sourcemodelusing twosonrces, one at0,15 mandone at 0,3 m. Above 2000 Hz figure 70 indicates that the result improve by adding one more source at 0,01 m.

-..

.s . . . . . ,...... ,....,,=,, .- .,. ..,, ,., ...... —- :.. .

6 Measurements on stationary vehicles

6.1 Description of measurements

The car was located on a grit surface and grassland respectively. The engine was run idling at 3000 rpm and the measurements were carried out at 7,5 and 15 m simultaneously on 4 different heights, the lowest of which was 0,3 m. . 6.2 Analysis of the results

In figure 72 a comparison between calculated and measured results are shown. The free field + 6dB level has been taken equal to the level above a grit surface which is probably not quite correct at high frequencies. The measured values are from measurements on the stationary car on grassland and the calculations have been made accordingly.

‘\ Source height i, I

0,3 , / / i \ /0 t ---- ‘o \/ / Measured , 00’2 /0 + I ----+.---- 6’ + 0,10 / + /- -1- 0,05 /

0,0

I I I

10’ 102 103 104 Frequency, Hz

Figure 72. Level re free field+ 6db 15 m in front of a Hyundai passenger car , Ill 111111 1! 1111111 Ill IIllt 11!111!11 111 111111 11111111 111 111 [11 111111111 !111!11 P 1 ii 111111 11 1 11! 111 II I ‘1 Ik 111 111111 I 1 1 I I I I I I Measdx! 1-!/1111 lfltllttl 1 1111)111- )/1 1,1/1111 -----l---i--l- . -$ -l- & l- !-l------l--- +--l-+-l-l-l-l ● l- L~-l. L-k-+ -L. 4-i-4 Ill liltii 1 Ill 111111 1 1111111!1 1 t II 111111 1 f 11 111111 1 111! 11111 1 ----4---4--1- - $ -l -l -l -l-l----- l--- +--l-+ -,+4 -Z-Z-Y-L 1 11 111111 1111 ‘1111 1 111111111 Ill 111! 1 rdiii!i 111 111111 111/ f 11111 11 I.l .1111 111 11(111. 11 illllt I 111111 I ;s=6,5’? ; : : : I 111111 111! 111! _lJ 11 II 1] II II II ---- J_-d_-l- J_ L-L LLl_____ L-_ L- J_l J-l-lJJ _----l--- L- 1.-l-l -lJ 111 111111 111111111 !1111 II 111 1111(1 111111111 11111 )1 111 111111 1! 1111111 11111 111 11! 111 111111111 11111 ll!ll! 111 111111111 11111 4! 111111111 11111 !111 11111 11 , , , I , , , , I I , , t t , , , , , I , , t , , t 10’ 102 103 104 Frequency, Hz Figure 73. Difference between 7,5m and 15 m at the receiver at 0,3 m.

5 11! 111111 111111 I I 11111!11 Ill 101111 111111 II 11111111 111 !11111 1! 1111 11 11111111 111111111 11 11111111 111111!11 &[\[[\ 11 11111111 11 I 1 I@l It 0 -__-;- 1 I I I LL-----J--L-1-LJ-1.9 )J-----;_::;;:_::;;:. 111111111 111111 11 Illllltl 111111111 11111 11 1111111! 111 111111 I 11 1111111 Ill 111111 1! m Ill 111111 11 u I 111111 11 -5 ---- 1 -- ;--:-J-LLLLL m- 11 11 -0 111 111111 11 II 111 w 111 111111 11 11 IAII III Ill 11 + 1 11 1 11 : -lo --_- L--~ -l- J-l- LLl-l--L_- f_- f-~~{----- .IJ-___-I---l_ L- LIJJJ. G 111111111 11 al 1! 1111111 111 l\tl 11 I al 111111111 111 l\ll 11 1 J= 11111 !111 111111 11 11111 !111 11111 11 8 al 111 !11111 11111 !1 I : -15 ---- L-_ J- J- J_t-LL Ll -- --- L-- L- J-LJ 1- 111 111111 111!1 II 9 Ill 111111 1111[ 11 1111111 3 111111111 1! 111 11 111111111 11111 11 111111111 111111 Ill 111111 111111 11 Ill 11111 -20 ---- L-_ J_ J- J_l_LL lJ -- --- L-- L- J- LJ-l Itl 111111 111111 11 11811111 11111 !111 111111 \ !t 111111111 111111 0: :1; ;[; ; ( 111 111111 111111 111111!11 111111 Ill 111111 111111 11111111 -25 I , 1 , , ! , , , , , f , , t , , L 10’ 102 103 104 Frequency, Hz Figure 74. Level re free field +6 db at 15 m and 0.3 m receiver height, 150 krayls and 0.3 m source height

Figure 74 indicates a very good a~eemeht at medium high frequencies. However, the agreement is not good at low and high frequencies. As to the high frequencies an alternative model using sound absorption might be used in stead. In figure 75 the sound absorption of the two ground types is shown and in figure 76 the result is illustrated. It seems that the ground absorption models in this c,aseworks better than the propagation model. ——. . ———. —

1 1 1! 11111 IO”= dlffusei i i i i i ii 1 11111111 1 11111 I I I - = perpenhicularl I I I I I I 0.9 ----- __ ;_---.-; --_lr__; _-; -+- ;+ -;------_; -.---+ ---; _- L-l,-- ! Al .& ..)’,, I 11111!1! I 11 1 11! 11111 9’::: 0.8 ------~_-._-.l--.-l‘ ~-, 1--,-, I l-l ~,-1------~----I 1 +n --,- ~- ;-r-,-r 1 11111111 ~1 11111 t 11111111 1 1111111! ------r---- ,--- r -<--,-q-l-< _, ----- ~,--$~:::::l --- ~---,--t-t- ~-1-~ 1 1[1 [1111 11111 I 11111111 I 11111111 ------>----1 ---l---l--l-+-l. ,lo-:___;4 - 1----+---!--+- ~ I :::;: +-l--l-l- 1 111!1 Y 1111111 1 !811 : ~>; :175 1 1111 Yls; ;;;:’” 1},1 ------l-----l --- L-J -J -- _--l----J--J-- L- J- L&lLL I II , C)<-; ;-:-- , , , , 1 I ;~;:::: II 1~:1: 1 1 /’7 !111111 u I c 1 g 0.3 u-l 1111111 0.2 11111 1! 11111 !111111 1111111 0.1 ------1 ---- 4 ---I--+-4-L .-l-b

0 , , , 9 , ! ! I , , , , I 102 103 104 Frequency, Hz Figure 75. Calculated ground absorption for grassland and grit surface respectively.

Difference gravel-grass at 7,5 m

10 / 2,5 m, measured,,, 4 m,,

m ‘- 4 a o c $2 ~ n o

-2

-4

-6 10’ 102 103 104 Frequency, Hz Figure 76. Difference between grit and grassland using statistical absorption theory in stead of propagation theory. 51

7 Determination of SEL, LpFxnaxand Lw

7.1 Difference between SEL and LpFma

The prime descriptor of road trafilc noise is Lw. This means that the most 10gical measurement quantity for individual vehicles should be the sound exposure level (SEL). .., ,.” However, for practical reasons it would be convenient to measure LPFmax and to calculate SEL as SEL measurements require more from the test environment. In order to be able to ;,- do so we need a source model which works well enough. Using the simplified model !“

described by eq. (1.2) we get the differences between SEL and LPFmax as shown in table G for passenger cars with 2 axles 2,5 m apart. For longer vehicles with more axles SEL will increase more than LPFmav

Table 6 Calculated difference between SEL and LpFmm at G 10 m and V= so ~ Range of integration SEL - LpFmm A 1,5 a (1,97 radians) 1,7 ~ 3 a ( 2,50 radians) 2,7 + 5 a ( 2,75 radians) 3,1 A 10a ( 2,94 radians) 3,4 + 100a ( 3,12 radians) 3,6

Table 5 shows the result to be expected assuming that the tyre/road radiation is omnidirectional in the horizontal plane and that the distance between the two wheel axes is 2,5 m. From figure 77 we can see that the point source model seems to work reasonably well for the frequency range 200-1000 Hz. Within this range the difference is between 2,3 and 2,9 d13compared to a calculated difference of 2,7 dE. The higher difference around 2000 Hz probably depends on the horn effect between tyre. More sound power is radiated forwards than sidewards.

5,5 5,0 -.. 4,5 4,0 3,5 # 3,0 E 2,5 u. ~ 2,0 J1 1,5 w (0 1,0 0,5 0,0 -0,5 -1,0 -1,5 Lnt.noomoomooo Inoooooooooo 00000 N ~-qlnco coomlcoo ml-o Omoomooomooo 00 s-7-,1- ml fNm-i-u)co moNcDoml-oo C900 m l-1-l- fNoJc9-a-mca coo

Frequency, Hz

Figure 77. 9 pass-by measurements on passenger cars at 50 * 3 km/h and 10 m distance and 4 m microphone height. SEL integration during+ 3 a

- ——. .- ... ,,. . ,,,...... - -“.. ,,, f,..~. ... ‘., --- .--— --- .—. .—— —

Another conclusion from figure 77 is that it is not possible to calculate the sound exposure level from the maximum level without introducing some directivity in the horizontal plane. In addition the maximum sound pressure is difficult to use in any case. , As was shown in 3.7.2 the maximum level will occur at different times or positions for different frequencies. Thus, even in the simple case for passenger cars, it seems more appropriate to use the sound exposure level than the maximum sound pressure level.

In figure 78 the corresponding pass-by measurements on two medium trucks are shown. we can see that the curves are quite different compared with the passenger cars.

4,0 , m 1

3,5

3,0

0,0

wmaocooomooo KJoooooooooo 00000 ml ~--lnmwoolwoul I- Oomoomooo U300000 ..70JoJcf)d-uy WCoonlwom. Oo moo m . ..nlnlm% Ulco coo

Frequency, Hz

Figure 78. 2 pass-by measurements on medium trucks with 3 axles at 53 and 60 km respectively and at 10 m distance and 4 m microphone height. SEL integration during ~ 3 a.

7.2 Calculation of LW and LPF~~X

According to eq. (1.5) the sound power level is obtained from

Lw = LE -W~ – C(v) (6.1)

where C(v) is calculated theoretically using a point source model coupled to propagation theory. Correspondingly we can calculate the maximum sound pressure level from

LP~mx= Lw – cm(V) (6.2)

In table 6.1 below these calculations have been carried out modelling the vehicle with 3 point sources at the heights 0,01; 0,15 and 0,30 m and assuming that the ground surface has the impedance 20000 kRayls. For the maximum sound pressure level the distance of calculation has been the shortest distance, that is 10 m. 53

Table 7 Measured and calculated values for a passenger car as reported in figure 64. Calculated from Measured Calculated source/propagation 9 pass-bys at 50~3 Ian/h model Frequency Lw– SEL LW- max SEL LPF- Lw LPF- i% C(50) cm(50) (El (i& dB dbB dlil 25 23,9 25,7 69,4 5,3 69,6 5,5 93,3 67,6 31,5 23,9 25,7 67,7 5,12 67,7 5,3 91,6 65,9 40 23,9 25,7 69,9 6,26 69,2 6,7 93,8 68,1 50 23,9 25,7 73,0 4,18 72,4 4,2 96,9 71,2 63 23,9 25,7 68,6 6,6 68,5 6,7 92,5 66,8 80 23,9 25,7 64,8 4,48 64,2 4,7 88,8 63,0 100 23,9 25,8 62,9 3,17 61,9 3,7 86,8 61,1 125 23,9 25,8 61,6 2,84 60,2 2,6 85,5 59,7 160 24,0 25,9 62,3 2,56 60,2 2,5 86,3 60,4 200 24,0 26,0 62,6 1,42 60,9 1,4 86,6 60,6 250 24,1 26,2 64,3 1,69 62,3 2,7 88,4 62,2 315 24,2 26,5 62,9 1,55 60,7 2,5 87,1 60,6 400 24,4 26,9 61,6 1,02 59,3 2,2 85,9 59,1 500 24,6 27,5 62,8 1,44 60,6 2,5 87,4 59,9 630 25,0 28,2 63,0 1,26 61,6 2,3 87,9 59,7 800 25,5 28,8 64,9 1,57 63,3 3,2 90,4 61,6 1000 26,3 28,8 67,3 1,56 65,5 2,2 93,6 64,8 1250 27,4 28,1 66,0 1,66 63,1 2,4 93,5 65,4 1600 28,4 27,8 63,4 1,42 59,5 2,3 91,8 63,9 2000 28,1 28,7 60,4 1,37 56,8 2,3 88,5 59,8 2500 26,4 27,7 58,5 1,01 55,4 2,2 85,0 57,3 3150 25,2 26,8 55,2 1,3 51,3 2,0 80,5 53,6 4000 25,9 28,7 52,6 1,55 49,8 2,1 78,4 49,7 5000 27,4 28,9 50,0 1,71 46,8 2,3 77,3 48,4 6300 27,1 28,5 47,1 1,95 44,2 2,9 74,2 45,7 8000 28,1 29,9 44,2 2,04 42,0 3,0 72,3 42,4 10000 28,9 30,6 40,8 1,88 39,1 2,7 69,7 39,1 A-weighted 73,5 71 72

Table 7 shows that the standard deviation of the sound exposure level is significantly smaIIer than that of the maximum leveI. This is another indication why it more suitable to work with sound exposure levels. The results are also illustrated in figure 79.

—- —— 54

75,0

70,0

65,0

%? 60,0 # E L = 55,0 -1

50,0

45,0 _ Calculated *

‘k \ 40,0

35,0 f

Frequency, Hz

Figure 79. Difference between measured and calculated levels for a passenger car.

From figure 79 we can see that the agreement is quite good, possibly with the exception of 1250–3150 Hz where the calculated values are systematically about 2 dB higher. This is probably due the homeffect, [9], between tyre and road surface. As more energy is radiating along the path of the car the maximum level which has been calculated perpendicular to the car is overestimated as the sound power has been distributed omnidirectionally.

In order to improve the result for 1250-3150 Hz it is possible to introduce a directivity to the earlier sound power level without changing the sound exposure level. If, e.g., the following sound power level is used

Lw + 7abs(cos(q)) – 1,7 (6.3) the maximum sound pressure level perpendicular to the vehicle will become 1,7 dB lower although the SEL-level will remain the same. 55

8 Discussion and conclusions

The measurements in clause 3.2 and 3.3 indicate that the effective sound source of a car has its centre close to the nearest wheels. For trucks this centre seed to be closer to the ,.- centre of the car. Assuming a shortest meas~ement distance around 7,5 m a variation .- between these two distances will cause an error in the sound exposure level of about 10 lg(7,5/6,5) = 0,6 dB. Because of this problem it is not recommendable to measure at too short distnces.

The vehicle as sound source is directional in the vertical plane. Between 100 and 800 Hz there seems to be some decrease of sound at all positions above the bottom of the car body. This is probably due to screening of the engine. Maybe the result will depend on the position of the exhaust but that has not been tested. At high frequencies there seems to be an increased directivity upwards. Because of the horn effect this directivity is most likely most pronounced in the direction parallel’to the wheels. Both effects seem to be less than about 2 dB for distances and heights practical to use for emission measurements.

The vehicle is also directional in the horizontal plane. The difference between SEL and LPF.Uvaries with frequency. The time histories of pass-byes shown in 3.6 also verifies a frequency dependence. At low frequencies interference effects between correlated sources may be the problem. At high frequencies the dnectivity of tyre/road noise affects the result.

The time when LPFn~ is obtained varies with frequency. Thus traditional maximum measurements are not suitable for frequency band applications.

Low frequency background noise is a problem below about 63 Hz. It seems to be a good and practical solution to use a low microphone position for these frequencies.

The measurements support the wellknown fact that the tyre/road noise source is very low. At high frequencies the source is probably only a centimeter or two above the road surface. At low and medium high positions the source height is not as critical as at high frequencies. The measurements on the stationary vehicle in 4 indicate that the engine source is also very low. At very low frequencies, below about 100 Hz, the location of the exhaust mouth is important.

The significant frequency dependence of the difference between SEL and LPF.mseems to make it worthwhile to measure both quantities. On the other hand the maximum level has. a high standard deviation and it is not always relevant for long vehicles.

With a proper source model it is possible to calculate the sound power level from pass-by measurements, at least in the direction of propagation. If the directivity is known the maximum sound pressure levels can be calculated from the sound power level.

The ground attenuation illustrated in clause 3.8 will be significant whenever we use low microphone positions and have some “soft” ground in between. Unless all measurements are restricted to propagation over “hard” surfaces only it is necessary to use rather high microphone positions. If these positions are too high directivity effects may affect the result.

-.. ,. ——.— — .- .,. ., ...... >. .,,5...... ?,., . . . . — — —— ——.——

9 Comparison measurements using Nordtest method

9.1 Introduction

A first proposal for Nordtest method was elaborated. The measurement method was according to the method given in annex A. However, the evaluation procedure was not decided upon until after the measurements.

It was decided to carry out the measurements at a suitable flat road section with an average speed around 50 km/h. The road surface should be dry, in good condition and with asphalt concrete. It was also decided to concentrate on light vehicles in order to get a sufficient number of vehicles. VTT did not carry out any measurements according to the method. In stead they used some older measurements of which only 3 could be used within the frequency range 50 t 2,5 kdh. The microphone height was 1,5 m in stead of 4 m and no frequency band data were taken for LpF~a.

The measurement results also indicated that the low microphone position at 0,4 m may be is not necessary, at least not for passenger cars. However, too little data at present is available to extrapolate that conclusion to heavy vehicles.

Traditionally A-weighted sound pressure levels are presented as a function of speed using regression analysis. In the present Nordic prediction model the SEL dependence on the speed follows 25 lg(v) and 30 Ig(v) for light and heavy vehicles respectively above 40 and 50 km/h respectively. The problem with this presentation is that we assume a certain behaviour, that is a constant slope, which may not always be true, in particular not if engine noise and tyre/road noise get different weighings. For trucks we have a breaking point at 50 lcrdh and assume a constant level below 50. Using regression only will not be able to identi~ such breaking points.

Another disadvantage with regression analysis is that the result may depend on the speed range used for the evaluation. The problems get worse if we require data in frequency bands. Each frequency band must have its on regression line and breaking points, if any may vary from band to band. For these reasons the Nordtest method recommends a presentation primarily vehicle by vehicle and secondarily as energy average determined from all measurements within ~ 2,5 km/h. Using a slope of 25 lg(v) at 50 km/h this correspond to a 1 dE difference between the extremes of the range. 57

9.2 Results

In the following only the results at 50 km/h are reported. All SEL-values have been corrected to correspond to an angle of integration corresponding to ~ 5 times the measurement distance.

Figure 80 and81 indicate that the Icelandic results deviate from those of the other Nordic countries. A possible explanation is that the the conditions are different. There are e.g many more terrain vehicles on Iceland. Figure 82 indicates that the measurement uncertainty improves at low frequencies if the speed interval is increased. This could be taken as a proof that a very large number of vehicIes are required in order to get accurate low frequency data.

50 km/h+2,5km/h

80,0 , I I I I I I I I I I I I I I I I I I I I I I I I I I I

55,0

50,0

45,0

40,0

Frequency, Hz

Figure 80. Normalized sound exposure level, LE,lo~.Energy average of all vehicles within 50 Ian/h t 2,5 kmfh.

—--i,.. --7— ----- 58

SEL, 50 km/h,+- 5 km/h

80,0

75,0

70,0

bx r I I I I I I

55,0

! ! I I I I I + Delta 50,0 I I I I I I I I 1 l+slm,~

45,0 I 1 I I I I I I I 1 I I I I I I I I I I m 40,0 I I I I I I I I I I i Intqoo mootno 00 U)ooooooo 00000000 -0 01 WU3cowocucoow I-00C300LO0 Oomooooo 0) . . . CNcd CO-3 u) al co o N a o In - 0 0 co o 0= z .-. Cumlccl=tu)cocoo ~ .— !? 4 Frequency, Hz

Figure 81. Normalized sound exposure level, Lfi,lO~.Energy average ofall vehicles within 50 Icm/h~ 5 kndh.

Sound exposure level

10,0-

9,0 t- —

8,0-

7,0

6,0 ~ , ,

5,0-

4,0- —

3,0- —

2,0- — —

1,0

0,0 m u-)-o o m o 0 In o 0 0 to o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 * N =tU-Jmmoolao O.oocooom Ooolnoooo 0< z -r. cuNmwlnuJcoo OJcoou).oocg 00 Frequency, HZ l--w a ccl -3 In mm o

Figure 82. Standard deviationoftheenergy averages reported in figure 80(excluding VTT)and81. LpFmax, dB SEL-LFmax, dB

co w s $. Cn m m o Cn o c-n o m o 25 -1 , 4 , i 31,5 L-----L-----L-----!-----+-----4------I 40 !-----i------i------:------l-----;------l 50 63 80 100 125 & 160 &l 200 rn 250 s l------i------i-----+------l-----+------l 315 3 -1------i------!------:------:-----+-----i ~ 400 Q. : 500 ------,------,-----+------+------:------1 ----- ; 630 -----.-j----.-+.----.-:----.--~ # 0 ------l------:------;------: ------:- ---- ~ 800 x I:; 11 s k;~o 3 ------.-.---,-.----..-:------{------:----- 1600 ------l------l------l------.------+-. ---: --:------2000 ------: --- --. -.: ------: -. -. .----:--- --1 J----- I 2500 w:l------i------i------l------l-----:------l 3150 ------~------:------;------:-----;----- 4000 -1---- -J------:------l-- --- J----- 5000 I----- , I 1 l----- J------I 6300 I I I ------1 ------1------1 ------1 ----- J ----- 8000 1 , I 1 1 ! 10000 -1------~------i------!------:-----ti-----i A- ---- .---1------1------1 ------1 ----- J------I 1 I I 1 ------1------1 ------1------1--- -- J-- --- I I I I 1 ------1 ------l------l------1- -. ----l ----- I 1 I 1 1

. ,-’ ... !, . . . . ,., , .“, - : .>” ,., . ,- .—— -.

50km/h k 5 kmlh

80 a , , , , , I I 8 , i I t 1 , I , , I 11111 !11, 1111 ,1,,, ,!, ,,, ,, 11111111 Inn, n,, 1,, ,,, ,, 75- :I:y,w:;:;w: :;::::::;:

35 tno 000000 00 00 NW 8omul ma Soo 0 . . N %’Coom too %0 . . N-t Wo

Frequency, Hz

Figure 85. Normalized maximum sound pressure level, LPF~a,lo~.Energy average of all vehicles within 50 km/h ~5 km/h

LpFmax

12,0 —

10,0 — — +45-55 km/t TPQJ=1’ — 8,0 — —

6,0 — —

— — 4,0 I \

— 2,0 i <

0,0 — T ~m-oocooom Oooln 00000 000000000 Ou WU-)(DCOOOJCQO !nl- Ooc?loo Lnoooloooo Ooa FI --- CNcvm -mw.OJo Cuwou-). oom oo~ ~-wNm-d’wJw mom- .-

Frequency, Hz

Figure 86. Standard deviation of the energy averages reported in figure 83 and 85. 61

10 References

[1] Vagtrafikbuller, nordisk berakningsmodell, reviderad 1996, Naturv&dsverket, Rapport 4653 [2] FHWA Traffic Noise Model, FHWA-PD-96-O1O,DOT-VNTSC-FHWA-98- 2, US Department of Transportation, 1998 [3] 1S0362:98 Measurement ofnoise efitted byaccelerating roadvehicles - Engineering method [4] SS-1S0 11819-1:97 Acoustics-Method for measuring the influence of road surfaces on traffic noise. Part 1: Statistical pass-by method [5] C.I. Chessell, 1977. Propagation of noise along a finite impedance boundary, Journal of the Acoustical Society of America 62,825-834 [6] Tomas Strom, Hans Jonasson, Bestamning av bulleremission friln stadsbussar, SP RAPPORT 1998:29. [7] H.G. Jonasson; 1973, A theory of traffic noise propagation with applications to L,~; JSV 30,289-304 [8] J-F. Hamet et al, Acoustic modelling of road vehicles for traffic noise prediction: Determination of the source height, ICA-ASA conngress, Seattle, 1998. [9] W. Kropp, F-X B6cot, S. Barrelet, On the sound radiation from tyres, manuscript, Chalmers, Sweden. [10] Birger Plovsing, Nerd 2000. Comprehensive outdoor sound propagation model. Part 1: Propagation in an atmosphere without significant refraction. To be published. [11] NT ACOU 104, Ground surfaces: Determination of the acoustic impedance.

— . .- . .X . .

62 63 ANNEx 2000-11-06 Proposal for Nordtest method

Vehicles: Determination of irnrnission relevant noise emission Contents

1 SCOPE AND FIELD OF APPLICATION 64 1.1 General 64 :’ 1.2 Measurement uncertainty 64 ..-

2 Normative references 64

3 Definitions 65 3.1 measurement distance, d 65 3.2 sound pressure, p: 65 3.3 sound pressure level, Lp: 65 3.4 maximum sound pressure level, LPFmax: 65 3.5 normalized maximum sound pressure level, LPFmax,lom: 65 3.6 sound exposure, E 65 3.7 sound exposure level, LE: 65 3.8 normalized sound exposure level, LE,lom: 65 3.9 frequency range of interest: 66 3.10 background noise 66

4 Instrumentation 66 4.1 General 66 4.2 Calibration 66 4.3 Vehicle speed measurement instrumentation 66 4.4 Temperature measurement instrumentation 66

5 Categories of vehicles and road surfaces 67 5.1 General 67 5.2 Vehicles 67 5.3 Road surfaces 68 5.4 Driving conditions 68

6 Test site 68 6.1 General requirements 68 6.2 Surface between the road surface and the microphones 69 6.3 Barriers and reflecting objects 69

7 Test procedure 69 7.1 Principle 69 7.2 Meteorological conditions 69 7.3 Microphone positions 69 7.4 Measurements 70 7.5 Criterion for background noise 70 7.6 Evaluation of the measurement results 71

8 Statement of the results 71

9 Information to be reported 72

Annex ABibliography Annex B Format for test results

. . ..—-—— ..,, .. .., ...... ?-. -. . -----,-.> ————.

1 SCOPE AND FIELD OF APPLICATION

1.1 General

This NORDTEST method specifies how to determine the noise emission of vehicles to obtain input data to be used in prediction methods for road traffic noise. The vehicles are measured one at a time. The method is applicable to all types of operating conditions and to all types of vehicles on all types of road surfaces provided that the measurement conditions are under control and reported. Many of the features of this NORDTEST method has been taken from ISO 11819-1.

1.2 Measurement uncertainty

The measurement uncertainty is given in table 1. The reported uncertainty is an expanded uncertainty based on a standard uncertainty of ORmultiplied by a coverage factor of k= 2, which provides a level of confidence of approximately 95Yo.The measurement uncertainty refers to the energy average of at least 20 vehicles within the speed interval to be investigated.

Table 1 Measurement uncertainty CR Expanded measurement uncertainty 25 Hz 6 f 12 31,5-63 Hz 4 ~8 80 Hz – 1000 Hz 3 *6 1250 – 10000 Hz 2 f4 A-weighted 1,5 f3

Note The measurementuncertaintyhasbeen estimatedfromcomparisonmeasurements carriedout at 4 differentplacesby 4 differentNordiclaboratorieson vehiclesof type 1aat 50 kmfh.

2 Normative references

The following standards contain provisions which, through reference in this text, constitute provisions of this Nordtest method. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this Nordtest method are encouraged to investigate the possibility of applying the most recent edition of the standards indicated below. Members of IEC and ISO maintain registers of currently valid international standards.

1S0 11819-1, Acoustics - Measurement of the injluence of road surfaces on traffic noise - Part 1: Statistical pass- by method IEC6065 1:1979, Sound level meters. lEC 60804:1985, Integrating-averaging sound level meters. LEC60942:1988”, Sound calibrators. IEC 61260:1995. Electroacoustics, Octave-band andfiactional-octave bandfilters.

64 65

3 Definitions

3.1 measurement distance, & ,.”

the horizontal distance between the microphone and the centre line of the vehicle)

3.2 sound pressure, p:

A fluctuating pressure superimposed on the static pressure by the presence of sound. It is expressed in pascals.

3.3 sound pressure level, Lp:

ten times the logarithm to the base 10 of the ratio of the square of the sound pressure to the square of the reference sound pressure (20pPa)

3.4 maximum● sound pressure level, LpFmax:

the highest instantaneous sound pressure level measured using time weighting F according toIEC6065 1.

3.5 normalized maximum sound pressure level, LpFmax,lom:

the maximum sound pressure level normalized to the reference distance 10 m.

,, 3.6 sound exposure, l?:

The time integral over a stated time-interval, T, of frequency weighted squared instantaneous sound pressure Pz(t), expressed in pascal-squared seconds.

E = Jpyt)u’t (1) o

3.7 sound exposure level, LE:

sound exposure level: Ten times the common logarithm of the ratio of sound exposure, E, to the reference sound exposure, Eo, expressed in decibels.

(2)

where, in air, E. is 400 ~Pa2s.

3.8 normalized sound exposure level, LE,lom:

the sound exposure level normalized to the reference distance 10 m.

. ..—— -. -. —. --- ,.. . --.—— —. .. .. ,. .._.

3.9 frequency range of interest:

For general purposes, the frequency range of interest includes the l/3-octave bands with rnidband frequencies from 25 Hz to 10000 Hz.

Note. The frequencyrangeof interestmayhaveto be restrictedin eitherdirectionbecause of too highbackgroundnoise.

3.10 background noise

noise from all sources other than the source under test.

NOTE Background noise may include contributions from airborne sound, structure-borne vibrationand electricalnoise in instrumentation.

4 Instrumentation

4.1 General

The measurement equipment shall meet the requirements of a class 1 instrument according to IEC 60651 and IEC 60804 and the filters shall meet the requirements of IEC 61260.

4.2 Calibration

During each series of measurements, apply a sound calibrator with an accuracy of *0,3 dB (class 1 according to IEC 60 942) to the microphone for checking the calibration of the entire measuring system at one or more frequencies over the frequency range of interest.

Verify the compliance of the calibrator with the requirements ofIEC60942 once a year and the compliance of the instrumentation system with the requirements of IEC 60651 at least every two years in a laboratory making traceable calibrations.

Record the date of the last check and confirmation of the compliance with the relevant IEC standard.

4.3 Vehicle speed measurement instrumentation

The vehicle speed shall be measured with an uncertainty of less than 3Y0.Measuring devices which rest on the road surface and are activated by the passage of vehicle tyres shall not be used.

4.4 Temperature measurement instrumentation

The temperature measuring instruments shall have a maximum error of 1°C. Meters using an infrared technique shall not be used for air temperature measurements.

46 67

5 Categories of vehicles and road surfaces

5.1 General

In order to have complete control of the measurement data it is necessary to keep track of as many parameters as possible. In the following the minimum requirements are given. In some cases it maybe appropriate to include even more parameters.

5.2 Vehicles

As a minimum the vehicles shall be divided into the following classes: Main Sub Category name Objective description category category 1 Cars la Passenger cars excluding other light vehicles 4 wheels, two axles lb Other light vehicles: cars with trailers or 4 wheels, two axles or 6 I Icaravans, light utility vehicles, minibuses, vans, Iwheels, 3 axles motor homes, recreational and utility vehicles 2 Dual-axle heavy vehicles. 6 wheels, two axles 2a City buses 6 wheels, two axles 2b Light and medium trucks 4-6 wheels, two axles 3 Multi-axle heavy vehiclesl) 3a Large city buses 8-10 wheels, 3 axles 3b Medium trucks 8-10 wheels, 3 axles 3C Heavy trucks 4-5 axles 3d Very heavy trucks >6 axles 4 Motor cycles 5 Mopeds ,,. ) Trailers, if any, included

Note Category1 is equalto that of ISO 11819. The other categories are different.

Indicate also if the vehicle has studded tyres. If the observer is uncertain about the classification of some passing vehicle, it shall be disregarded or put in a “special class”.

,4,.,,,...-r~-~~+ —-—,.. , ...... - -...... ’ .-...... —. . ——. —

5.3 Road surfaces

As a minimum the roa i surfaces shall be divided into the following 8 main categories: Main ISub Name

Asph. concr., dense, smooth (<12-16 mm) I Amh. concr.. dense. smooth (< 8-10 mm) I Mastic asphalt (SMA) (max 12-16 mm) Mastic asphalt (SMA) (max 8-10 mm) 3 3a Chipped asphalt (BCS) (“hot rolled asph.”) I 3b Chip seal, single (Yl), max 16-20 mm I 3C Chip seal, single (Yl), max 10-12 mm I 3d Chip seal, single (Yl), max 6-9 mm 4 I 4a Chip seal, double (Y2), max 16-20 mm I 4b Chip seal, double (Y2), max 10-12 mm 5 5a Porous asph., max 14-16mm (*20%voids) 5b Porous asph., max 8-12 mm (*20% voids) 6 6a Cem. concr., dense, smooth* 20-80 mm += 6b Cem. concr., dense, smooth, * 12-18 mm I 6C Cem. concr., ground (grinding not worn) 7 I Paving stones, cobble stones (older type) 8 Cement block pavement (interlocking) Note The diffel mt categories have been taken from the Nordic prediction method for road traftlc noise.

Indicate also if the road surface is dry, wet, icy or snow covered. In addition indicate the temperature of the road surface. Describe or photograph the surface.

Preferably use also sub categories together with the age of the road surface and the yearly traffic flow.

5.4 Driving conditions

Category Name Objective description 1 Cruising Constant speed and gear 2 Acceleration Continuous acceleration) 3 Deceleration Continuous deceleration) 4 Uneven Both acceleration and deceleration 1)E.g. aftercrossings,trafficlightsor speedlimit signs 2)E.g. beforecrossings,trat%clightsor speedlimit signs

6 Test site

6.1 General requirements

The road shall be essentially level and straight. The road section shall extend at least 3 times the measurement distance on both sides of the microphone location The number of vehicles shall be sufficient to get a representative sample and at the same time small enough to avoid disturbing background noise from vehicles other than the vehicle under test

68 69

. The road surface shall be in good condition unless the intention is to study the effect of the condition

6.2 Surface between the road surface and the ,.- microphones

The ground attenuation between the edge of the road and the microphone shall be minimized for any frequency band of interest. With the measurement procedure of this NORDTEST method this requirement is considered to be met if at least half the area between the centre of the test lane and the microphones have acoustical properties equivalent to (or “harder” than) those of the road surface used for the tests.

Note It is easierto complywiththeserequirementsif the measurementare carriedout on vehiclespassingby on the lanefarthestawayfromthe microphones.For vehicleswith a screened exhauston one side it maybe necessaryto measurein two directions.

6.3 Barriers and reflecting objects

There shall be no barriers, such as solid safety barriers, guardrails of metal beams or embankments between the path of the vehicle and the microphones. Transparent wire or cable fences are allowed.

No reflecting obstacles which may influence the measurements by more than 0,5 dB are allowed unless the obstacle is a large facade on which the microphones are mounted, see ,,’ clause 7.3.

7 Test procedure

-. 7.1 Principle

The principle is to measure individual vehicle pass-bys under representative conditions and to obtain data affected as little as possible by the ground attenuation between the vehicle and the microphone. The method uses two fixed microphone positions, the bottom and the top microphone respectively. To minimize the risk of underestimating the sound pressure level due to unforeseen interference or directivity effects the highest value, after distance correction, of the two microphone positions is taken as the result of the measurement. All measurement results are corrected to the reference distance 10 m.

7.2 Meteorological conditions

The wind speed shall not exceed 5 rds when measured at a height of 1 m above the ground.

Note 1 To minimize turbulence due to thermal and wind gradients it is recommended to carry out the measurements when the sky is overcast and the wind speed low.

Note 2 At low frequencies the wind may affect the noise emission from the vehicle due to increased aerodynamic noise or increased load on the engine.

7.3 Microphone positions

Select a measurement distance, d, as close as possible to 10 m. The distance selected shall be within the interval 7,5-15 m. d shall be kept within A 0,5 m if the variations are

, .

70 reasonably evenly distributed around the centre line and within ~ 0,3 m if the variations are unevenly distributed around the centre line. If the variations are greater each vehicle has to be assigned its own d.

Note A short distance is to prefer when the background noise is high or when the conditions on maximum ground attenuation cannot be met. Else a longer measurement distance is to prefer.

Use two microphone positions , one at 0,2 m and one at 4 m. Measure the heights along the normal to the surface of the average ground plane. When defining the ground plane exclude vegetation such as grass. Direct the microphones towards the tyre/road intersection.

Locate the microphone either away from all reflecting surfaces or fastened directly on a large reflecting surface parallel to the road. When flush-mounted its axis shall be parallel to the plane of the facade and directed upwards or downwards or with its axis pointing towards the test specimen along its normal. The distance from the facade to the centre of the 13 mm microphone membrane shall be 7 mm or shorter if the upper frequency limit is 5000 Hz or 3 mm or shorter if the upper frequency limit is 10000 Hz, if the axis of the microphone is parallel to the test surface. If the axis is normal to the test surface the distance shall be half of that of parallel mounting. In order to achieve distances short enough it is necessary to mount the microphone embedded in a plate or board. If fastened, the microphone shall be fastened to the test specimen with a strong, adhesive tape. Equip the microphone with a hemispherical windscreen, see figure 2.

Figure 2. Flush-mounted microphone

7.4 Measurements

Measure the speed of the vehicle, the temperature of the road surface, L~ and LP~- during each pass-by and record the category of vehicle and the driving conditions.

Note LPF- will occur at different times for different frequencies. Thus the measured A- weighted maximum level will differ from the A-weighted maximum level calculated from the maximum of the different frequency bands.

Start the measurement when the vehicle is at the distance 3d in front of the normal from the microphones to the road or earlier, but not earlier than 5d, and stop it when it is at the same distance or later behind the normal.

In order to achieve the measurement uncertainty stated in this Nordtest method measure on at least 20 vehicles within each speed interval to be investigated.

7.5 Criterion for background noise

70 71

For each frequency within the frequency range of interest the background noise shall be at least 6 dB and preferably at least 10 dB below the level of lowest sound pressure level during a pass-by. No corrections are allowed.

Note The background noise level at the highest microphone position maybe significantly higher than that of the lower position.

7.6 Evaluation of the measurement results

For each individual vehicle, for each one third octave band and for each microphone position, calculate the normalized sound exposure level using the following equation: >,.

L~,lom = LE + 10 lg (=F .Io,g[‘a] M10 2 arctan(5) where

LE= the sound exposure level measured d= measurement distance, in m w = the axle width of the vehicle (= 0,75 m for cars and 1,25 m for trucks unless other information is available) h,= height of the microphone (0,2 m and 4 m respectively) ZICZ= angle of circular sector covering the line of integration, in radians

The result is given by the highest value from the two microphone positions.

Note 1 If the sound power level is to be calculated it may be necessary to distinguish between values obtained from the high and the low microphone respectively.

Note 2 At low frequencies wind and background noise will often influence the sound pressure level more at 4 m than at 0,2 m. Thus it is important to make sure that the highest sound power level calculated, if derived from measurements at 4 m, is not affected by background noise.

The normalized maximum sound pressure level is calculated from

L (4) pFInax,lom = LPF.+UW 10 “

H Note For long vehiclesthis formulamaynot be as accurateas the correspondingformula for the soundexposurelevel.

8 Statement of the results

State the result of each individual vehicle pass-by using the format given in annex B. In addition, for each frequency band, calculate the energy mean value of each speed interval defined by a centre speed, evenly dividable by 5, ~ 2,5 Ms. State the result with one decimal together with the standard deviation and the number of measurements within each interval.

-—-...... r...... ---- ...... -7— ...... ,, ———— ——

9 Information to be reported a) State that the measurements have been carried out in full conformity with this Nordtest method. Any deviations shall be reported. b) State, for each individual vehicle, for each third octave band and A- weighted, the sound power level, the sound exposure level and the maximum sound pressure level. c) State the temperature of the road surface either as an average, or, if the variations are greater than 5°, or for each individual vehicle pass-by d) State, for each vehicle, vehicle category, driving conditions and speed. e) State road category.

72 73

Annex A Bibliography (Informative)

Hans G. Jonasson, Measurement and modelling of noise emission of road vehicles for use in prediction models, Nordtest project 1452-99, I@B-project 1998-0659, KFB project 1997-0223, SP REPORT 1999:35

,, ..

—. --- ...... ~ — -- Annex B – Format for test results (informative) Test conditions Mic height 4 0,2 Vehicle 1A 1A Half axle width 0,75 0,75 Road surface lb lb Distance 9 9 Da 2,56 2,56 Speed 48 48 hast ml-s 13,3 13,3 Korsatt 1 1 Air temp 18,6 18,6 Road temp 29,8 29,8 Cloudiness 80% 80Y. Wind speed <5 <5 Measured SEL, dB 25 75,3 77 31,5 73,8 74,3 40 71,9 72,5 50 71,5 73 63 77,6 79,1 80 68,4 69 100 71,1 72,3 125 64,2 65,1 160 62,6 62,9 200 64,0 65 250 66,6 66,7 315 63,7 63,4 400 62,6 62 500 62,7 62,2 630 63,6 63,8 800 67,7 68,1 1000 68,1 68,5 1250 65,1 66,3 1600 63,1 65 2000 59,7 60,7 2500 57,1 59,5 3150 54,5 57 4000 51,9 53,9 5000 47,1 50,4 6300 43,9 47,1 8000 40,5 42,3 10000 37,1 39 A-weighted 74,0 Max(0,2 m, 4 m) Normalized (10 m) SEL 25 74,9 76,5 76,5 31,5 73,4 73,8 73,8 40 71,5 72,0 72,0 50 71,1 72,5 72,5 63 77,2 78,6 78,6 80 68,0 68,5 68,5 100 70,7 71,8 71,8 125 63,8 64,6 64,6 160 62,2 62,4 62,4 200 63,6 64,5 64,5 250 66,2 66,2 66,2 315 63,3 62,9 63,3 400 62,2 61,5 62,2 500 62,3 61,7 62,3 630 63,2 63,3 63,3 800 67,3 67,6 67,6 1000 67,7 68,0 68,0 1250 64,7 65,8 65,8 1600 62,7 64,5 64,5 2000 59,3 60,2 60,2 2500 56,7 59,0 3150 54,1 56,5 56,5 4000 51,5 53,4 53,4 5000 46,7 49,9 49,9 6300 43,5 46,6 46,6 8000 40,1 41,8 41,8 10000 36,7 38,5 38,5

A-weighted 73,6