DOCSLIB.ORG

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

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Hans G. Jonasson Measurement and Modelling of Noise Emission of Road Vehicles for Use in Prediction Models Nordtest Project 1452-99 KFB Project 1998-0659/1 997-0223 -.. SP Swedish National Testing and Research Institute SP Acoustics SP REPORT 1999:35 .— 2 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. .~. —.. .- ?.. 4 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.
Recommended publications
  • 6. Units and Levels

    6. Units and Levels

    NOISE CONTROL Units and Levels 6.1 6. UNITS AND LEVELS 6.1 LEVELS AND DECIBELS Human response to sound is roughly proportional to the logarithm of sound intensity. A logarithmic level (measured in decibels or dB), in Acoustics, Electrical Engineering, wherever, is always: Figure 6.1 Bell’s 1876 é power ù patent drawing of the 10log ê ú telephone 10 ëreference power û (dB) An increase in 1 dB is the minimum increment necessary for a noticeably louder sound. The decibel is 1/10 of a Bel, and was named by Bell Labs engineers in honor of Alexander Graham Bell, who in addition to inventing the telephone in 1876, was a speech therapist and elocution teacher. = W = −12 Sound power level: LW 101og10 Wref 10 watts Wref Sound intensity level: = I = −12 2 LI 10log10 I ref 10 watts / m I ref Sound pressure level (SPL): P 2 P = rms = rms = µ = 2 L p 10log10 2 20log10 Pref 20 Pa .00002 N / m Pref Pref Some important numbers and unit conversions: 1 Pa = SI unit for pressure = 1 N/m2 = 10µBar 1 psi = antiquated unit for the metricly challenged = 6894Pa kg ρc = characteristic impedance of air = 415 = 415 mks rayls (@20°C) s ⋅ m2 c= speed of sound in air = 343 m/sec (@20°C, 1 atm) J. S. Lamancusa Penn State 12/4/2000 NOISE CONTROL Units and Levels 6.2 How do dB’s relate to reality? Table 6.1 Sound pressure levels of various sources Sound Pressure Description of sound source Subjective Level (dB re 20 µPa) description 140 moon launch at 100m, artillery fire at gunner’s intolerable, position hazardous 120 ship’s engine room, rock concert in front and close to speakers 100 textile mill, press room with presses running, very noise punch press and wood planers at operator’s position 80 next to busy highway, shouting noisy 60 department store, restaurant, speech levels 40 quiet residential neighborhood, ambient level quiet 20 recording studio, ambient level very quiet 0 threshold of hearing for normal young people 6.2 COMBINING DECIBEL LEVELS Incoherent Sources Sound at a receiver is often the combination from two or more discrete sources.
  • Definition and Measurement of Sound Energy Level of a Transient Sound Source

    Definition and Measurement of Sound Energy Level of a Transient Sound Source

    J. Acoust. Soc. Jpn. (E) 8, 6 (1987) Definition and measurement of sound energy level of a transient sound source Hideki Tachibana,* Hiroo Yano,* and Koichi Yoshihisa** *Institute of Industrial Science , University of Tokyo, 7-22-1, Roppongi, Minato-ku, Tokyo, 106 Japan **Faculty of Science and Technology, Meijo University, 1-501, Shiogamaguti, Tenpaku-ku, Nagoya, 468 Japan (Received 1 May 1987) Concerning stationary sound sources, sound power level which describes the sound power radiated by a sound source is clearly defined. For its measuring methods, the sound pressure methods using free field, hemi-free field and diffuse field have been established, and they have been standardized in the international and national stan- dards. Further, the method of sound power measurement using the sound intensity technique has become popular. On the other hand, concerning transient sound sources such as impulsive and intermittent sound sources, the way of describing and measuring their acoustic outputs has not been established. In this paper, therefore, "sound energy level" which represents the total sound energy radiated by a single event of a transient sound source is first defined as contrasted with the sound power level. Subsequently, its measuring methods by two kinds of sound pressure method and sound intensity method are investigated theoretically and experimentally on referring to the methods of sound power level measurement. PACS number : 43. 50. Cb, 43. 50. Pn, 43. 50. Yw sources, the way of describing and measuring their 1. INTRODUCTION acoustic outputs has not been established. In noise control problems, it is essential to obtain In this paper, "sound energy level" which repre- the information regarding the noise sources.
  • Sony F3 Operating Manual

    Sony F3 Operating Manual

    4-276-626-11(1) Solid-State Memory Camcorder PMW-F3K PMW-F3L Operating Instructions Before operating the unit, please read this manual thoroughly and retain it for future reference. © 2011 Sony Corporation WARNING apparatus has been exposed to rain or moisture, does not operate normally, or has To reduce the risk of fire or electric shock, been dropped. do not expose this apparatus to rain or moisture. IMPORTANT To avoid electrical shock, do not open the The nameplate is located on the bottom. cabinet. Refer servicing to qualified personnel only. WARNING Excessive sound pressure from earphones Important Safety Instructions and headphones can cause hearing loss. In order to use this product safely, avoid • Read these instructions. prolonged listening at excessive sound • Keep these instructions. pressure levels. • Heed all warnings. • Follow all instructions. For the customers in the U.S.A. • Do not use this apparatus near water. This equipment has been tested and found to • Clean only with dry cloth. comply with the limits for a Class A digital • Do not block any ventilation openings. device, pursuant to Part 15 of the FCC Rules. Install in accordance with the These limits are designed to provide manufacturer's instructions. reasonable protection against harmful • Do not install near any heat sources such interference when the equipment is operated as radiators, heat registers, stoves, or other in a commercial environment. This apparatus (including amplifiers) that equipment generates, uses, and can radiate produce heat. radio frequency energy and, if not installed • Do not defeat the safety purpose of the and used in accordance with the instruction polarized or grounding-type plug.
  • Monitoring of Sound Pressure Level

    Monitoring of Sound Pressure Level

    1. INTRODUCTION Noise is one of the main environmental problems of modern life and it is inseparable from human activities, urban and technological growth. National and international standards provide for a minimum of acoustic comfort for coexistence between man and industrial development. That's why a study of noise emission and environmental noise at the PALAGUA - CAIPAL Field was carried out; samples of measurements were taken in specific (punctual) manner to meet the sound pressure level (SPL) with a duration of five minutes per sample/measurement for noise measurements and 15 minutes for ambient or environmental noise in each direction: (north, east, south, west and vertical). The result of these measurements was compared with the maximum permissible noise emission and environmental noise standards stated in Resolution 627 of 2006 Ministry of Environment, Housing, and Territorial Development (MAVDT) and thus it was verified that they comply with environmental regulations in the PALAGUA - CAIPAL Field. 1 INFORME DE LABORATORIO 0860-09-ECO. NIVELES DE PRESIÓN SONORA EN EL AREA DE PRODUCCION CAMPO PALAGUA - CAIPAL PUERTO BOYACA, BOYACA. NOVIEMBRE DE 2009. 2. OBJECTIVES • To evaluate the emission of noise and environmental noise encountered in the PALAGUA - CAIPAL Gas Field area, located in the municipality of Puerto Boyacá, Boyacá. • To compare the obtained sound pressure levels at points monitored, with the permissible limits of resolution 627 of the Ministry of Environment, SECTOR C: RESTRICTED INTERMEDIATE NOISE, which allows a maximum of 75 dB in the daytime (7:01 to 21:00) and 70 dB in the night shift (21:01 to 7: 00 hours) 2 INFORME DE LABORATORIO 0860-09-ECO.
  • Sound Power Measurement What Is Sound, Sound Pressure and Sound Pressure Level?

    Sound Power Measurement What Is Sound, Sound Pressure and Sound Pressure Level?

    www.dewesoft.com - Copyright © 2000 - 2021 Dewesoft d.o.o., all rights reserved. Sound power measurement What is Sound, Sound Pressure and Sound Pressure Level? Sound is actually a pressure wave - a vibration that propagates as a mechanical wave of pressure and displacement. Sound propagates through compressible media such as air, water, and solids as longitudinal waves and also as transverse waves in solids. The sound waves are generated by a sound source (vibrating diaphragm or a stereo speaker). The sound source creates vibrations in the surrounding medium. As the source continues to vibrate the medium, the vibrations propagate away from the source at the speed of sound and are forming the sound wave. At a fixed distance from the sound source, the pressure, velocity, and displacement of the medium vary in time. Compression Refraction Direction of travel Wavelength, λ Movement of air molecules Sound pressure Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average, or equilibrium) atmospheric pressure, caused by a sound wave. In air the sound pressure can be measured using a microphone, and in water with a hydrophone. The SI unit for sound pressure p is the pascal (symbol: Pa). 1 Sound pressure level Sound pressure level (SPL) or sound level is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level. The standard reference sound pressure in the air or other gases is 20 µPa, which is usually considered the threshold of human hearing (at 1 kHz).
  • Guide for the Use of the International System of Units (SI)

    Guide for the Use of the International System of Units (SI)

    Guide for the Use of the International System of Units (SI) m kg s cd SI mol K A NIST Special Publication 811 2008 Edition Ambler Thompson and Barry N. Taylor NIST Special Publication 811 2008 Edition Guide for the Use of the International System of Units (SI) Ambler Thompson Technology Services and Barry N. Taylor Physics Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899 (Supersedes NIST Special Publication 811, 1995 Edition, April 1995) March 2008 U.S. Department of Commerce Carlos M. Gutierrez, Secretary National Institute of Standards and Technology James M. Turner, Acting Director National Institute of Standards and Technology Special Publication 811, 2008 Edition (Supersedes NIST Special Publication 811, April 1995 Edition) Natl. Inst. Stand. Technol. Spec. Publ. 811, 2008 Ed., 85 pages (March 2008; 2nd printing November 2008) CODEN: NSPUE3 Note on 2nd printing: This 2nd printing dated November 2008 of NIST SP811 corrects a number of minor typographical errors present in the 1st printing dated March 2008. Guide for the Use of the International System of Units (SI) Preface The International System of Units, universally abbreviated SI (from the French Le Système International d’Unités), is the modern metric system of measurement. Long the dominant measurement system used in science, the SI is becoming the dominant measurement system used in international commerce. The Omnibus Trade and Competitiveness Act of August 1988 [Public Law (PL) 100-418] changed the name of the National Bureau of Standards (NBS) to the National Institute of Standards and Technology (NIST) and gave to NIST the added task of helping U.S.
  • Noise Exposure Limit for Children in Recreational Settings: Review of Available Evidence

    Noise Exposure Limit for Children in Recreational Settings: Review of Available Evidence

    Noise exposure limit for children in recreational Make Listening Safe settings: review of WHO available evidence This document presents a review of existing evidence on risk of noise induced hearing loss due to exposure to sounds in recreational settings, with respect to children. The evidence was used to stimulate discussion for determination of exposure limits (in children) to be applied to standards for personal audio devices. The review has been undertaken by February 2018 Dr Benjamin Roberts under the supervision of Dr Richard Neitzel, in collaboration with WHO. The document has been reviewed by members of WHO expert group on exposure limits for NIHL in recreational settings. Noise exposure limit for children in recreational settings: review of available evidence Authors: Dr Benjamin Roberts Dr Richard Neitzel Reviewed by: Dr Brian Fligor Dr Ian Wiggins Dr Peter Thorne 1 Contents List of Tables 1 List of Figures 1 Definitions and Acronyms ............................................................................................................................. 2 Executive Summary ....................................................................................................................................... 3 Background and Significance ........................................................................................................................ 4 How Noises is Assessed............................................................................................................................. 5 Overview of the Health
  • Lumens and Loudness: Projector Noise in a Nutshell

    Lumens and Loudness: Projector Noise in a Nutshell

    Lumens and loudness: Projector noise in a nutshell Jackhammers tearing up the street outside; the In this white paper, we’re going to take a closer look at projector noise: what causes neighbor’s dog barking at squirrels; the hum of it, how to measure it, and how to keep it to a minimum. the refrigerator: noise is a fixture in our daily Why do projectors make noise? lives, and projectors are no exception. Like many high-tech devices, they depend on cooling There’s more than one source of projector noise, of course, but cooling fans are by systems that remove excess heat before it can far the major offender—and there’s no way around them. Especially projector bulbs cause permanent damage, and these systems give off a lot of heat. This warmth must be continuously removed or the projector will overheat, resulting in serious damage to the system. The fans that keep air unavoidably produce noise. flowing through the projector, removing heat before it can build to dangerous levels, make noise. Fans can’t help but make noise: they are designed to move air, and the movement of air is what makes sound. How much sound they make depends on their construction: the angle of the blades, their size, number and spacing, their surface quality, and the fan’s rotational speed. Moreover, for projector manufacturers it’s also key not to place a fan too close to an air vent or any kind of mesh, or they’ll end up with the siren effect: very annoying high-frequency, pure-tone noise caused by the sudden interruption of the air flow by the vent bars or the mesh wires.
  • Measurement of Total Sound Energy Density in Enclosures at Low Frequencies Abstract of Paper

    Measurement of Total Sound Energy Density in Enclosures at Low Frequencies Abstract of Paper

    View metadata,Downloaded citation and from similar orbit.dtu.dk papers on:at core.ac.uk Dec 17, 2017 brought to you by CORE provided by Online Research Database In Technology Measurement of total sound energy density in enclosures at low frequencies Abstract of paper Jacobsen, Finn Published in: Acoustical Society of America. Journal Link to article, DOI: 10.1121/1.2934233 Publication date: 2008 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Jacobsen, F. (2008). Measurement of total sound energy density in enclosures at low frequencies: Abstract of paper. Acoustical Society of America. Journal, 123(5), 3439. DOI: 10.1121/1.2934233 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. WEDNESDAY MORNING, 2 JULY 2008 ROOM 242B, 8:00 A.M. TO 12:40 P.M. Session 3aAAa Architectural Acoustics: Case Studies and Design Approaches I Bryon Harrison, Cochair 124 South Boulevard, Oak Park, IL, 60302 Witew Jugo, Cochair Institut für Technische Akustik, RWTH Aachen University, Neustrasse 50, 52066 Aachen, Germany Contributed Papers 8:00 The detailed objective acoustic parameters are presented for measurements 3aAAa1.
  • Solid-State Memory Camcorder

    Solid-State Memory Camcorder

    4-425-717-13(3) Solid-State Memory Camcorder PMW-200 PMW-100 Operating Instructions Before operating the unit, please read this manual thoroughly and retain it for future reference. © 2012 Sony Corporation WARNING • Refer all servicing to qualified service personnel. Servicing is required when the To reduce the risk of fire or electric shock, apparatus has been damaged in any way, do not expose this apparatus to rain or such as power-supply cord or plug is moisture. damaged, liquid has been spilled or objects To avoid electrical shock, do not open the have fallen into the apparatus, the apparatus cabinet. Refer servicing to qualified has been exposed to rain or moisture, does personnel only. not operate normally, or has been dropped. WARNING Do not install the appliance in a confined When installing the unit, incorporate a readily space, such as book case or built-in cabinet. accessible disconnect device in the fixed wiring, or connect the power plug to an easily IMPORTANT accessible socket-outlet near the unit. If a fault The nameplate is located on the bottom. should occur during operation of the unit, WARNING operate the disconnect device to switch the Excessive sound pressure from earphones power supply off, or disconnect the power plug. and headphones can cause hearing loss. In order to use this product safely, avoid Important Safety Instructions prolonged listening at excessive sound • Read these instructions. pressure levels. • Keep these instructions. • Heed all warnings. For the customers in the U.S.A. • Follow all instructions. This equipment has been tested and found to • Do not use this apparatus near water.
  • Sound Waves Sound Waves • Speed of Sound • Acoustic Pressure • Acoustic Impedance • Decibel Scale • Reflection of Sound Waves • Doppler Effect

    Sound Waves Sound Waves • Speed of Sound • Acoustic Pressure • Acoustic Impedance • Decibel Scale • Reflection of Sound Waves • Doppler Effect

    In this lecture • Sound waves Sound Waves • Speed of sound • Acoustic Pressure • Acoustic Impedance • Decibel Scale • Reflection of sound waves • Doppler effect Sound Waves (Longitudinal Waves) Sound Range Frequency Source, Direction of propagation Vibrating surface Audible Range 15 – 20,000Hz Propagation Child’’s hearing 15 – 40,000Hz of zones of Male voice 100 – 1500Hz alternating ------+ + + + + compression Female voice 150 – 2500Hz and Middle C 262Hz rarefaction Concert A 440Hz Pressure Bat sounds 50,000 – 200,000Hz Wavelength, λ Medical US 2.5 - 40 MHz Propagation Speed = number of cycles per second X wavelength Max sound freq. 600 MHz c = f λ B Speed of Sound c = Sound Particle Velocity ρ • Speed at which longitudinal displacement of • Velocity, v, of the particles in the particles propagates through medium material as they oscillate to and fro • Speed governed by mechanical properties of c medium v • Stiffer materials have a greater Bulk modulus and therefore a higher speed of sound • Typically several tens of mms-1 1 Acoustic Pressure Acoustic Impedance • Pressure, p, caused by the pressure changes • Pressure, p, is applied to a molecule it induced in the material by the sound energy will exert pressure the adjacent molecule, which exerts pressure on its c adjacent molecule. P0 P • It is this sequence that causes pressure to propagate through medium. • p= P-P0 , (where P0 is normal pressure) • Typically several tens of kPa Acoustic Impedance Acoustic Impedance • Acoustic pressure increases with particle velocity, v, but also depends
  • Aircraft Noise (Excerpt from the Oakland International Airport Master Plan Update – 2006)

    Aircraft Noise (Excerpt from the Oakland International Airport Master Plan Update – 2006)

    Aircraft Noise (Excerpt from the Oakland International Airport Master Plan Update – 2006) Background This report presents background information on the characteristics of noise. Noise analyses involve the use of technical terms that are used to describe aviation noise. This section provides an overview of the metrics and methodologies used to assess the effects of noise. Characteristics of Sound Sound Level and Frequency — Sound can be technically described in terms of the sound pressure (amplitude) and frequency (similar to pitch). Sound pressure is a direct measure of the magnitude of a sound without consideration for other factors that may influence its perception. The range of sound pressures that occur in the environment is so large that it is convenient to express these pressures as sound pressure levels on a logarithmic scale that compresses the wide range of sound pressures to a more usable range of numbers. The standard unit of measurement of sound is the Decibel (dB) that describes the pressure of a sound relative to a reference pressure. The frequency (pitch) of a sound is expressed as Hertz (Hz) or cycles per second. The normal audible frequency for young adults is 20 Hz to 20,000 Hz. Community noise, including aircraft and motor vehicles, typically ranges between 50 Hz and 5,000 Hz. The human ear is not equally sensitive to all frequencies, with some frequencies judged to be louder for a given signal than others. See Figure 6.2. As a result of this, various methods of frequency weighting have been developed. The most common weighting is the A-weighted noise curve (dBA).