Research Department. REPORT No. B.014 9th October, 1936. o J Serial No. 1936/13
Work carried out by Drawing Nos. B.014.l A. B. Howe. toB.014.l2. J. McLaren. A. L. Newman. ACOUSTICS OF MAIDA VALE sruDIOS.
SU1~. This report describes the considerations leading to the design of the various studios at Maida Vale. An epitome specification is given in each case. The results of reverberation measurements in each studio are discussed in their relation to the acoustical treatment and to the practical results obtained.
Studios 2 and 3, and 4 and 5 form two pairs designed for the purpose of experiment relating to the acoustical effect of variations in studio form. The results of the experiment are given and possible explanations discussed.
Modifications to the studios now in hand are considered.
The report is of an interim character •.
INTRODUCTION.
Maida Vale studios were intended to provide accommodation
supplementary to that available in Broadcast.ing House, catering
particularly for the musical side of the programmes. In the final
BBC R & 0
111111111111111111111111111111111111111111111111111111111111 300008835 R ------j ,/
-2-
. scheme, five studios were provided. No. 1 is a large orchestral
studio capable of accommodating a full symphony orchestra. Nos. 2
and 3 are orchestral studios equivalent, in a general way, to the
Concert Hall in Broadcasting House. Nos. 4 and 5 are general purpose
music studios roughly equivalent to studio BA in Broadcasting House.
The studios are practically independent structures built
inside the shell of a disused skating rink. All are built of thick
bri.ckwork and have independent roofs below the main roof of the
building. This method of construction was designed in part so as to
provide the maximum sound inSUlation between the various studios.
Additional sound insulation from street noises is provided, much as in \ Broadcasting House, by offices, recording rooms etc., which abut directly
on the street.
In each case the actual studio roof or ceiling is supported
by steel t~sses or girders, and consists of lath and plaster on heavy
wooden joists. The upper side of the joists is covered with 1"
boarding and the space between them packed with sawdust 'and shavings.
This type of ceiling was specified with the object of reducing both
structura) resonance and sound interference.
The· foregoing remarks apply to all studios alike. The
characteristics of the individual studios will now be considered
separately. -3-
STUDIO No. 1.
This studio was intended to supersede "No.10 studiol1 and to accorrrrnodate the full BBC symphony orchestra of 119 perfo:!;,mers for rehearsal purposes, and even occasionally for transmission. A volume of about 250,000 cubic feet was therefore required. Although adequate floor area could be obtained there was some limitation as regards height, owing to the existing roof of the building and to the undesirability of excavating, In order to get the maxlimwn possible height, the usual restriction regarding the use of a flat ceiling was relaxed, and the design shovm in Fig. 1 was adopted. The average height was about 28'-6", the overalllength of the studio 125 ft. and the width 72 ft. The actual volume of the studiO, allowance being made for gallery, beams etc., is 230,000 cubic feet.
Acoustical Treatment. At the time a decision was made as to the acoustical treatment, -i" building board cemented to a hard rigid surface was still believed to hav~ a sensibly flat absorption-frequency characteristic with a value of absorption coefficient of about 0.25.
As precautions had been taken to avoid structural resonance, it was thought that an ideal type of reverberation-frequency characteristic would be the result of the use of this material.
The usual limits of reverberation time in BBC practice, for a studio of the size in question, are 1.9 and 2.4 seconds. A value -4-
of 2.1 seconds was actually adopted as the basis of the calculation of
the treatment.
The following is an outline of the treatment. The floor was
covered entirely with building board and carpet with an underfelt, the
area being 7920 sq. ft. 6500 sq. ft. of board were also ap~lied to
the wallS, representing an area of about 85% of the total wall surface
and leaving a plaster dado four feet high. The ceiling was untreated.
Tvvelve heavily upholstered setliBes were also included as part of the acoustical treatment.
Reverberation Measurements. The reverberation-frequency characteristic
of the studio was determined in the usual manner. In view of the possibility of sound concentration effects due to the shape of the roof, two series of measurements were made. For one series the microphone was suspended at about 8 feet from the floor and for the other at about
4 feet, the usual height in our reverberation measurements. This procedure arose from the fact that in preliminary experience in the practical use of the studio, which had been gained before it was possible to make reverberation measurements, a relatively high microphone position had been found to reduce the bass-heaviness which had been experienced. Five microphone positions were used for each series.
In addition to these measurements, decay curves were plotted -5-
for a ce~tral microp4one position, by measuring the time for various values of'decay from 10 to 40 or 45 db., according to ground noise conditions. These measurements confirmed the legitimacy of the usual method of extrapolation from a value of about 30 db., and this was done for the principal series of measurements.
The results of the reverberation measurements are shown in
Table I and are plotted in Figs. 2 and 3(a). Fig. 2 shows the curves for high and low microphones respectively, and Fig. 3(a) the mean of the two series. It was not feasible to obtain a value of 62.5 cycles for the high position owing to the low sound intensity obtainable, and the reading for the low position must be accepted with reserve. The curve below 125 cycles is therefore dotted in.
Conclusions from Reverberation Measurements. Considering first the curve of Fig. 3(a), it is eVident that the studio is too live for frequencies below 1000 cycles per second, and that the reverberation time falls off somewhat too rapidly for the higher frequencies. The latter fact is readily explained in terms of the relatively large proportion of carpeted building board used in the treatment. This feature was, of course, foreseen and was unavoidable on account of the proportions of the studio, on the assumption that carpet was tQbe used for the floor. It was considered to be acceptable in practice.
The high reverberation at low frequencies was not understood at the time the curve was determined, since precautions had been taken -6- to avoid structural resonance in walls and ceiling. It is readily explained, however, in terms of the now known absorptive properties of building board; in fact, were it not for a certain amount of absorption provided by the ceiling, considerably longer reverberation for frequencies below 250 cycles would occur.
Referring now to the two curves shown in Fig. 2, confirmation is obtained of the theory that concentration of sound due to the shape of the ceiling occurs for frequencies below about 400 cycles. The method of reverberation measurement used is such that if the initial sound intenSity before cutting off the source is non-uniform, a high initial intensity tends to give a low value of measured reverberation til'OO and vice versa. Hence ·a higher j.ntensity, at low frequencies, occurs near the floor than at, for example, a height of 8 feet. This result was also obtained in the practical use of the studiO, a high microphone position being found to reduce the effect of bass. It was also supported by ripple tank experiments.
In the latter experiments the assumption was made that pure reflection, as in optics, occurs from the ceiling surfaces for sound waves of the higher frequencies, but that for low frequencies the ceiling behaves as a cylindrical surface, 'in accordance with accepted theory. Models were made representing these two conditions.
For the case representing low frequency behaviour, it was -'7-
easily seen that sound originating from a source near the floor, after
bei~g reflected twice from the ceiling and once from the floor was
brought to a focus just above floor level. For the high frequency
case, a much reduced focussing effect was observed, owing to the
scattering effect of the various ceiling surfaces. Another factor
tending to reduce the effect of the roof for the higher frequenCies
is the considerably increased absorption for the single reflection from the floor.
The focussing effect produces a reflected component of high
intensity which gives interference effects with the direct ray from the source and causes the undesirable effects inseparable from standing wave patterns, as well as l!bass-heaviness Y1 • The conclusion is that
concave ceilings must be avoided in future in studio construction, even if they are composed of large plane surfaces. A similar effect has been noticed in the Birmingham studiO, which has a similar ceiling.
Effect of the Studio in Practice. The actual use of the studio for
orchestral work was attended with fair success so far as the result heard via the microphone was concerned. Some observers considered the effect to be extremely good; others thought it was too reverberant, particularly at low frequenCies. Difficulties of balance, poor string tone and excessive bass existed, however, only partially solved by the use of a high microphone and other expedients such as a relatively -8-
close teclmique. Volume control was difficult for passages involving
heavy bass, owing partly to the interference effects and partly to the
high general bass intensity due to insufficient low frequency absorption~ .
Conductors and players have also complained that the studio is too
reverberant and that contact is difficult to maintain.
Remedial Measures. Completely satisfactory acoustics could only be
attained by an entirely fresh acoustical treatment giving the
appropriate absorption at all frequencies, the ceiling being one of the
areas to be treated. This is not, however, a practicable solution at present. Experience in orchestral balance has shown that a platform
or raked staging for the orchestra, similar to that employed inmost
concert halls, is a considerable aid in obtaining a satisfactory
balance. Such a platform has nm~ been designed and constructed, the
scheme being combined with that for the installation of an organ. A plan view of the platform is shown in Fig. 4. It is of wooden
construction on tubular steel scaffolding and is uncarpeted, but
covered with linoleum. It has resulted in a considerable improvement
in acoustical conditions as regards listening both in the studio itself
and via the microphone. The general effect is one of greater brilliance,
so that a much more distant micropho~e 'technique can be employed with advantage, with no deteriorat ion of string tone. Bass intensities are
still too high, with normal orchestral playing, but bass definition has been considerably improved. -9-
Reverberation curves have been determined,for the low and high microphone positions respectively, corresponding with those originally taken. The results are given in Table II and plotted in
Fig. 5. The mean of the two curves, representing the general reverberation curve of the studio in its present condition is shown as
Fig. 3(b), for direct comparison with the curve of Fig. 3(a). Such a comparison shows, in the first place, that the woodwork of the platform has had a definite, though not a very marked effect in reducing the reverberation time for low frequencies.
In the redetermination of the reverberation time," the loud speru~er was placed on the top rise of the platform in the position normally occupied by the bass instruments, in order that the curves might indicate any change in the concentration effects due to the new position. A comparison of Figs. 2 and 5 shows that such a change has indeed taken place. The divergence between the two curves is not quite so marked under the new conditions, and actually the longer reverberation time now tends to be associated with the low microphone position instead of with the high. Thus the low microphone position would be expected to give, on the whole, lower sound intensities for . . bass instruments on the platform than the high microphone position.
The evidence of the reverberation measurements would thus appear to be" that the improvement which has been noticed with regard -10-
to bass quality is due partly to the absorption of low frequency energy
by the woodwork and partly to an alteration of the sound concentration
. effects.
The improvement. in brilliance is certainly not due to any
change in the reverberation conditions, since the old and ~ew curves
are.practically identical for frequencies above 500 cycles per second.
Two causes seem possible; the better arrangement of the players with
regard to the microphone and the consequent reduction of masking of
one performer by another, also the reduction of high frequency
absorption near to the source by the us·e of linoleum instead of carpet
for the floor. Probably'both effects contribute.
That the studio is still somewhat too reverberant· is confirmed
by the fact that for loud playing a noisy and confused effect is
produced, particularly for listening in the studio itself. Although
permanent re-treatment is not yet feasible, it would be very desirable
to experiment with temporary modifications to the acqustical treatment. , . This could be done very effectively by draping the ceiling with long
strips of Cabot's quilt, suspended tent-wise to the tops of the side
walls. This would yrovide the desirable reduction of reverberation
time, and would considerably reduce the concentration effect. It
would be effective at low frequencies owing to the spaci~g of the
quilt from the reflecting surface above, and would enable the optimum -11-
reverberation time to be confirmed by direct experiment. This
procedure is therefore recommended.
STUDIOS Nos. 2 and 3.
These two studios were intended for use by orchestras of
moderate size, such as sections C, D and E of the BBC orchestra and
by the Military Band and similar combinations. studio, . No. 2 has a
volume of 60,500 cubic feet, and No. 3 one of 62,900 cubic feet. Each was suitable, therefore, for normal use, for 30 performers, with a maximum of 45. The length, breadth and height of each studio were
11 respectively 71'-6 , 44'-Oi? and 19'-3" respectively. The difference
in volume is due to the special configuration of the wall surface, as
described below, associated with studio No. 2.
Acoustical Design and Treatment. In constructing a pair of studios
such as Nos. 2 and 3, it was desired not only to provide the necessary
studio accommodat~on, but also to make an experiment to test the
acoustical properties of "broken H wall surfaces as compared with plane
surfaces. Accordingly the design of wall configuration shown in Fig.
6 was devised for studio No. 2, the ceiling being similarly broken up.
The graduation of the length of the corrugations was decided upon in
oruer that the sound waves reflected from the walls might be mixed as
completely as possible and no new regularity produced, for example, by -12- a series of evenly spaced partially reflecting surfaces. Both studios are rectangular in ground plan, and No.3 has plane walls and ceiling.
The corrugations of the walls of studio No. 2 were formed by building out in solid brickwork, the minimQ~ thickness of the wall being
11 9 and the maximum 2' -3" 0 In the case of studio No. 3 the wall thick- ne ss is 1 f -6 i1, so that the total we ight of brickwork in the tviTO studios is approximately the same. The outside dimensions are the same for the two studios, so that the volume of the corrugated studio is slightly the lesser as mentioned above. The general ceiling construction of both studios is the same as that of studio No. 1, but a more complicated type of steelwork was necessary in the case of studio No. 2.
Building board was used for the acoustical treatment, partly for the reason stated in connection with No. 1 studio and partly so as to introduce no new unknown factor into an experiment relating to studio form. ' The usual limits of reverberation time for these studios, from consideration of their volume, are L33 and 1.63 seconds respectively.
The higher value was selected as the basis for calculation of treatment, as engineering opinion was, at the time, in favour of relatively long reverberation for music studios.
The floors were covered entirely with building board and carpet, with an underfelt, the areas concerned being 2900 sq. ft. and
3140 sq. ft. respectively for studios 2 and 3. The walls of the -13-
.studios ymre covered with 'building board except for a hard plaster dado having a height of 3'_9" in studio 2 and 2'-9 iV in studio 3.
The ceilings consisted of distempered plaster in both studios.
Reverberation Measurements. The results of measurements of the reverberation frequency characteristics of these two studios are given in Table 111 and are plotted in Fig. 7.
It will be seen that except for frequencies below 125 cycles per second the reverberation curves of the two studios are practically coincident, the observed discrepancy being hardly outside the possible experimental error. The difference for the lower frequencies is attributed to the difference of roof structure rendered necessary by the corrugated roof of stUdio No. 2. As is now known considerably more rise of reverberation time for the lower frequencies would occur, were it not for a certain amount of low frequency absorption associated with the ceilings.
Further, the requirements forming the basis of calculation of the treatment are well fulfilled for frequencies above 500 cycles per second, although the low frequency rise is more than experience has shown to be desirable.
Effect of the studios in Practice. studio No. 3, the plane-walled studio, shows preCisely, in practice, the characteristics which would be expected after study of its reverberation curve. Whilst the result -14- as heard via the loudspeaker is good, some difficulty is experienced in the placing of the bass instruments, and the sound intensity which they produce tends to be too high, sometimes causing difficulties of control.
This is not unexpected, seeing that the high reverberation time at low frequencies is due to lack of absorption rather than to any structural resonance. The general opinion, also, is that the studio is rather too reverberant, qUite apart from the question of prominence of bass. Thus the use of the higher limit of reverberation ttme in studio design appears unjustified.
The acoustical effect of studio No. 2, the corrugated studio, is however, very different from that of studio No. 3, and may be expressed in a general way by the statement that it seems much more fldead" than its reverberation curve would suggest. Nevertheless, aural estimation of the actual time taken for a simple sound to reach inaudibility is practically the same in the two studios, confirming the reverberation measurements. The result, with an orchestra playing in
No. 2 studio, is not good. Not only is the result too IIdead?i, but the effect of a somewhat confused background is produced.
For a Military Band,. however, the studio is good. The deadness is considered desirable and the individual parts stand out clearly. The only difficulty which exists is that of maintaining
IIcontact Ii between the performers, probably owing to the fact that -l5- instrumentalists do not hear a direct undistorted first reflection from the "broken ,I walls. In an endeavour to improve conditions as regards contact as well as to give general assistance in balancing the band, a concert platform, similar to that installed in studio No. 1, has been designed and constructed.
A reverberation curve has been taken with the concert platform in /osition, the loudspeaker being placed high up on the platform. The results are given in Table IV, and are plotted and compared with the original curve in Fig. 8. The reduction of the reverberation time for the low frequencies is even more marked than in the case of studio No.l.
This is to be expected, as the size of the platform is greater in relation to the volume of the studio than in the latter studio. A slight reduction of reVerberation time for frequencies above 1000 cycles also appears to have taken place, but no ready explanation is available.
From consideration of the reverberation characteristics some improvement in the acoustics of the studio would be expected, apart from the aiding of balance and contact, for which the platform was designed.
Sufficient experience has not, however, yet been gained to enable an opinion to be given on this point.
Explanation of Observed Effects. The results described above are contrary to recognised acoustical theory and consequently require explanation, as a contribution to the science of acoustics as well as -16- to provide data for future studio design. Various possibilities have been suggested and same have been tested by experiment, but the investigation is not complete, nor has a fully satisfactory explanation been found. It seems not unlikely that more than one factor may contribute towards the production of the effect as heard by the ear. A brief outline follows of the suggestions made and of the results so far obtained.
(1) It was possible that the broken surface might tend to suppress air resonance in No. 2 studio, whilst such resonance could easily occur in No. 3 studio. Were this the case one might expect the sound intensity to build up a much higher equilibrium value in the latter studio than in the former, although the rate of decay remained nearly the same, This was test'ed by experiment, using a loudspeaker as the source of sound. A negative result was obtained, the sound intensities being practically identical in the t·wo studios.
(2) Classical theory states that the effect of broken wall surfaces such as those of studio No. 2 must vary greatly with the frequency of the sound waves concerned. At low frequencies the walls should be indistinguishable from plane walls, whilst at high frequencies the reflections must take place iiopticallyl1 in accordance with the configuration of the walls, the paths of the rays of sound being very different fram those in a studio with plane llvalls. .An intermediate -17-
condition occurs for waves of length comparable with the size of the
corrugations, the ray being split up into two components, one of which
is reflected as from a plane wall and the other deviated by diffraction.
In fact for medium frequencies the action of a corrugated wall is
analogous to that of a diffraction grating in the case of a ray of
light, separating a complex wave into its different components, the
direction of the reflected ray depending upon frequency.
This means that a ray of complex sound originating from an
orchestral instrument, for example, loses its identity on reflection
from the broken wall, on account of the separation of its components.
Moreover, these must get more and more separated at each successive
reflection, so that the reverberative sound, whether from a single
instrument or from an orchestra, at least over the middle range of
frequencies, is merely a mixture of unrelated components, and no
individual ray can possibly be identified as originating from any
particular instrument. Thus the acoustical effect which would be
expected would be a clear and acoustically "deadl1 impression of the
orchestra due to the direct unreflected ray, standing out against a
background of thoroughly mixed components having an energy content, as
a function of frequency, dependent upon the characteristics of the
orchestra and of the sound absorption in the studio. In a studio with
plane walls, on the other hand, one would expect the various components, -18- over wide ranges of frequency, to be reflected in the same way, so that it should be possible to detect, in the reverberative sound, components associated with particular instruments. Thus the reverberative sound should blend with the direct sound rather than form an unrelated back- ground.
(3) Another possibility is that owing to the complexity of the paths taken b~ the rays of sound in a studio such as No. 2, by comparison with the relative simplicity of the conditions in a plane walled studio, the decay of sound intensity may not be logarithmic, at least over part of the decay period. In other words, the rate of decay may itself be a function of time. This suggestion was tested experimentally by taking decay curves in 5 db. steps for each of the five usual microphone positions in both studios 2 and 3. These measurements were necessarily very laborious, and would have been much simplified by the use of an instrument such as the Neumnnn
tl iiPegelschreiber 0
,In studio 3, the decay was found to be sensibly logarithmic for all fre~uencies for which tests were made, i.e., over the range 125 to 4000 cycles. In studio 2, however, a definite tendency towards an
S-shaped configuration, for the curve of log. intensity plotted against time, was found for the middle frequencies, roughly between 200 and 1500 cycles. At 125 cycles no distinction could be drawn between the results in the two studiOS, and the same applied very largely to -19- measurements, at 2000 and 4000 cycles. Thus it appears that this phenomenon is experienced for frequencies such "as to show diffraction effects as explained earlier in this report. Typical decay curves for studios 2 and 3 respectively are shown in Figs. 9 and 10. The curve for 2000 cycles in Fig. 9 and for 1000 cycles in Fig. 10, have been omitted for clearness owing to their overlapping other curves. It will be seen that for the S-shaped curve the centre portion is linear, but that the rate of decay is greater than the overall rate.
On the reasonable assumption that the ear appreciates the middle part of the decay, e.g., from 10 to 30 db., one explanation is found of the apparent deadness of studio 2. Fig. 7(c) shows a new reverberation curve for the studio, computed on the basis of the rate of decay of the mid-portion of the decay curves, for comparison with the curves measured in the usual way. For studio 3 no such revised curve can be drmm..
STUDIOS 4 and 5.
These two studios were intended for the use of relatively small musical combinations and for ilgeneral purpose\! use. No. 4 has been used almost exclusively by the BBC Dance Orchestra. Studio No.4 has a volume of 25,400 cubic feet, and No. 5 of 26,000 cubic feet ..
They are suitable, therefore, for use by up to 17 performers under normal Circumstances, and for a maximum of 25 performers. Their -20- approximate length and breadth are 45 and 30 feet respectively and their
11 height 19'-6 •
Acoustical Design and Treatment. These two studios were intended for use in an experiment to test the difference, as observed in practice, between studios with rectangular as compared with non-rectangular ground plan. Fig. 11 shows the ground plan of studio 4, studio 5 being rectangular. Both studios had plane walls. The general structure of the two studios was the same as that of studios 2 and 3, and building board was again used for the acoustical treatment.
The limits of reverberation tune for both studios are 1.1 and 1.3 seconds. li seconds was therefore used as the basis of calculation of acoustical treatment, for the reasons already described.
In both studios the walls were covered entirely with building board except for a hard plaster dado 3 feet in height. The floors were carpeted over building board, and the ceiling? were of distempere~ plaster.
Reverberation Measurements. The results of measurements of the reverberation frequency characteristics of these two studios are given in Table V and are plotted in Fig. 12. The two curves are practically identical. No importance is to be attached to the apparent peak at 88 cycles for studio No. 5, owing to the difficulties of measurement at the lowest frequencies and the consequent relative inaccuracy. The same remarks as to the general shape of the curves apply as in the case of -21- studios 2 and 3.
Effect of the Studios in Practice. No difference has so far been detected between the acoustical effects of these two studios. Both studios have proved to be somewhat too reverberant, particularly at the lower frequencies. The conclusion is that there is no practical advantage to be gained by making studios with non-parallel walls, in spite of the importance which has been attached to such a practice by certain foreign acoustical engineers.
In view of the use of studio No. 4 for the Dance Orchestra, for which relatively dead conditions are desirable, it has been necessary to add absorbing material to reduce the reverberation time to a suitable value. These experiments, however, will be the subject of a separate report.
CHF. -22-
TABLE I.
Reverberation Times of studio No. 1, Maida Vale.
Frequency. Reverberation Times (seconds).
4 ft. high. 8 ft. high. Mean.
62 cycles. 3.30
125 IV 2.83 3.16 3.00
250 11 3.05 3.52 3.28
500 Ii 2.79 2.71 2.75
1000 11 2.24 2.25 2.25
2000 11 1.73 1.74 1.74
4000 11 1.43 1.32 1.37
8000 If 0.95 1.08 1.02 -23-
TABLE IT.
Reverberation Times of studio No. 1, Maida Vale,
after addition of Concert Platform.
Frequency. Reverberation Times (seconds).
4 ft. hiSh. 8 ft. high. Mean.
62 cycles. 2.99 2.09 2.54
88 If 2.45 2.59 2.52
125 IV 2.94 2 0 51 2. '73
11 175 2 0 96 2.64 2.80
250 I! 2.75 2.74 2.75
350 I! 2.95 2.91
500 1Y 2.36 2.65 2.50
700 11 2.36 2.42
1000 " 2.10 2.20 2.15
1400 IV ---- (1.96)
2000 ?i 1.76 (1.76)
2800 IV 1. '70 (1.'70)
4000 VI 1.36 (1.36)
5600 11 1.32 (1. 32)
8000 11 1.16 (1.16 )
NOTE. Measurements with a high microphone position were not taken for frequencies above 1000 cycles per second as, on the basis of previous experience, it was considered extremely unlikely that any divergence would be outside the possible experimental error. The l'meanVi figures, shown in brackets; therefore depend on the single series of measurements. -24-
TABLE Ill.
Reverberation Ttmes of studios 2 and 3, Maida Vale.
Frequency. heverberation Tlines (seconds) •
studio 2. Studio 3.
62 cycles. 3.04 4.32
88 Ii 3.05 3.70
125 Ii 3.13 3.05 175 " 2.36 2.80
250 11 2.21 2.27
350 11 1.83 2.11
500 11 1.62 1.79
700 !Y 1.56 1.60 1000 " 1.64 1.76 1400 !Y 1.66 1.86
2000 Ii 1.51 1.56
2800 !Y 1.44 1.51
4000 !Y 1.14 1.21
5600 li 1.07 1.12
8000 !Y 0.82 0.89 -25-
TABLE IV.
Reverberation Times of Studio 2, Maida Vale, with Concert Platform.
Frequencz· . Reverberation Time (seconds) •
62 cycles. 2.35
88 11 2.49
125 11 2.18
175 I! 1.96
250 I! L89 350 " 1.98 500 11 1.'75
'700 iI 1.62
1000 VI 1.55
1400 II 1.42
2000 ii 1.32
2800 II 1.14
4000 it 1.00
5600 if 0.94
8000 iI 0.84 -26-
TABLE V.
Reverberation Times of studios 4 and 5, Maida Vale.
Frequency. Reverberation Time (seconds) •
studio 4. studio 5.
62 cycles. 2.64 2.44
88 If 2.38 2 .. 87
125 !I 2.01 2.24
1'75 i1 2.11 2.20
250 If 1.81 2,.02
350 !I 1.63 1.68
500 If 1.41 1.44
'700 1I 1.45 1.42
1000 iI 1.30 1.38
1400 11 1.29 1.32
2000 11 1.17 1.21
2800 Ii 1.14 1.10
4000 IV 0.85 0.83
5600 iI 0.89 0.81
8000 if 0.70 . O. '70 '"l:j t-I Q • ~
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i GROUND PLAN OF CpRRUGATED STUDIO AT MAID! VALE. . I: FIGi~6.
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SCALE- 8 FEET TO 1 INCH. REPORT B .OH. 6. CCNTF 5.0 3.0 2.0 1.0 N Frequency in periods per second. REPORT. B.014.7...... N ....t o t CA (l) -- -- 12-10-35·1 I I nu fn; I (:!;jj~:HH;:b !ilJJm··:i1L!1:trilrl.y~! niU1B~ITFP${uIDt,·~tD:illil14$Sl!~.#klmt;~i;"t;;. ~~ :r=ffi!l~l: ~~j;':~~:i~; '~lt to: llJi er Tt") .::;'''T 1"'1'1+ ... j ~j Jfrl1ffitjtF;~7J7mit.r~~ ."~-n-, I ,'1-.' 't [-h -,,'"" rl]"Tr~;:;:;-~J:f.}i~ i:'TtETT:n :ftp+rrl ..31rt'l.j~i[itfLtP:t* P-l;- ;Tl-t1~~~ rt-,+},. {11:[ilTI:1HiJ.111F;i", '-t"," -;',,""1", d-l:- '~"i j I, :ll1Imn;:l:-1-~" . _~" ~,. 1: 'ft'J". Fl} . If!rg~!,_, 1: J.H: • _ _ 1_ ;t:~__ __ ~lif: __ lq:+; ::::~! Fhltlltt{;tmr:i-t4~ . Lt .• +~~ I:: Et,PI rr 1ft fi'iJJT' "-art _i.+lF"HL' H#f+f:P=th lli~rf:fflj :l:[1frl n ,.·:CJ ':CJ I·' t' !-l!tll~mhj:rITcf '~j:j .1 t{B:!Jt~~i: "tttt· ~LilfIr £ -;- ,~- . tt:.l ····!J.w .rtflr·iP.~~l lW.i·;. .",,ftif~8{l;,'ftIJllM_jj t'·! l,1.1. "1:. ,p •.. .. ·11' t' tL.. ·n ± -~·.t!:t'·~·· . .·gfrJ-rtl:tr ... :.rIJulL., .. ,. ,1·, 1..::: Ill.. ··-WT. tt.. lt;: :1 "C 1 ·''··IF.t~ u Lt~·· it· ..tR tt:i' .'"'""tttF ~t L,d¥:: 1+ ·:fhlb ·~:rL:-·-h ut" •• 1.' flf.lJ-· :P.:8' "l± .:.·' r ',1: _. fr-~.- . tf {+-,_. 'n" .·m~"l· ;.ill±1... tt"1.- :r I' H" ffH ·I.i~'-·· ii ttn;ftlf .• !.;.tttl1·tttttl.ttt: ·,fmIftIT ~t-rltl··t·,:!· . " .. ~.-.• .J:l:lfP~~ .:. L It fl) .~ ...... o· .....1 .r. h',. -11 11 STUDIO No.4. I Microphone Skirting Observation Windo..,. WAITING ROOM. LIST:~NING ROOM. i I SCALE- 8 FEET TO 1 INCH • • 1· I B. B. I~. R1:: SE:ARCH DEPT. FIG.ll.. GROUND PLAN OF STUDIO No.4.: DRN. ~ R~:PORT • B.014.11. DATA St1£"ET No. 16 SPECIAL. P~''''N nF"pr/()01JCT!<:·N Co., C£NTAAL HOU:>F. 45 K!NG~.v .... Y. W.C.2. I f' ;... Frequency in periods pe,. second.