J

Research Department. REPORT No. B.014 9th October, 1936. o

Serial No. 1936/13

Work carried out by A. B. Howe.

Drawing Nos. B.014.l 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

/ ,

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. 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.

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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

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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

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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

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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

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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

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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.

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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

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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

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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

respectively 71'-6 11, 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

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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

911 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

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.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

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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

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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

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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

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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 "dead l1 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,

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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

iiPegelschreibertl 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

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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

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approximate length and breadth are 45 and 30 feet respectively and their

height 19'-611•

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

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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.

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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

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TABLE IT.

Reverberation Times of studio No. 1, Maida Vale,

after addition of Concert Platform.

Frequency.

62 cycles.

88 If

125 IV

175 11

250 I!

350 I!

500 1Y

700 11

1000 "

1400 IV

2000 ?i

2800 IV

4000 VI

5600 11

8000 11

Reverberation Times (seconds).

4 ft. hiSh.

2.99

2.45

2.94

2 0 96

2.75

2.95

2.36

2.36

2.10

1.76

1. '70

1.36

1.32

1.16

8 ft. high.

2.09

2.59

2 0 51

2.64

2.74

2.91

2.65

2.42

2.20

----

Mean.

2.54

2.52

2. '73

2.80

2.75

2.50

2.15

(1.96)

(1.76)

(1.'70)

(1.36)

(1. 32)

(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.

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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

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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

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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

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EXTERNAL STUDIO WALL. WALL.

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SCALE- 16 FEET TO 1 INCH.

EXTERNAL PITCHED ROOF.

STUDIO WALL.

EXTERNAL WALL.

GROUND LEVEL.

4.0

13.0 r

2.0

1.0

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Frequency in periods per second.

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Frequency in periods per second. B. '8. c. DRN.

APPD.~ B.0]4.3.

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STUDIO WALL.

ORGAN. ORGAN.

ROSTRlJM.

SCALE- 8 FEr';T TO 1 INCH.

4.0

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N

Fr.,quency in periods per second.

eE~TRAL. HOUSE:. 45 K:N~S'''A'I'. "'V C.2.

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ORN. REPORT. t APPD. 8.014.5. J

16-9-36.

i

GROUND PLAN OF CpRRUGATED STUDIO AT MAID! VALE.

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SCALE- 8 FEET TO 1 INCH. REPORT B .OH. 6.

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REPORT.

B.014.7.

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12-10-35·1

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Observation Windo..,.

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SCALE- 8 FEET TO 1 INCH • • 1·

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FIG.ll.. GROUND PLAN OF STUDIO No.4.:

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B. B. I~. R1:: SE:ARCH DEPT.

DRN. ~ R~:PORT •

B.014.11.

DATA St1£"ET No. 16 SPECIAL.

Frequency in periods pe,. second.

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