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RESEARCH DEPARTMENT 

SOUND INSULATION AND ACOUSTICS 
IN THE BELFAST STUDIO CENTRE 

Report No. B. 059 
Serial No. 1954/38 



C. L. S. Gilford, M. Sc, A.M. I.E. E. , F.Inst. P. 

W. K. E. Geddes, M. A. Syf0 uc/ o* A-M*** ' 

M.W. Greenway, M. Sc. (Eng. ) ■ T 

A. L. Newman, A. R.P.S. 

F.L. Ward, B. Sc. , A.M. I.E. E. (*• Proctor Wilson) 



Report No. B.059 

S0UKTD INSULATION" AND ACOUSTICS 

IN" THE BELFAST STUDIO CENTRE 



Section Title Page 

SUMMARY 1 

1 INTRODUCTION 1 

2 SOUND INSULATION BETWEEN ' STUDIOS 2 

2.1. Insulation Between Studio No. 1 and Adjacent Studios 2 

2.2. Insulation Between Studios Nos. 3 and 5 3 

2.3. Insulation of the Continuity Studios 3 

2.4. Insulation Between the Control Room and Studios Nos. 3 and 5 . 3 

2.5. Insulation of Studios Nos. 2 and 6 3 

2.6. Studio-to— Cubicle Insulation 4 

2.7. Discussion of Inter-Studio Insulation 4 

3 GENERAL ACOUSTICS 5 

3.1. Studio No. 1 (75,000 ft 3 ) Orchestral Studio 5 

3.2. Studio No. 2 (4,000 ft 3 ) Talks Studio 5 

3.3. Studios Nos. 3 and 5 (6,300, 6,700 ft 3 ) Drama Studios 6 

3.4. Studio No. 4 (4,100 ft 3 ) Effects Studio . . 7 

3.5. Studio No. 6 (1,500 ft 3 ) Talks Studio 7 

3.6. Studio No. 8 (30,000 ft 3 ) General Purpose Studio 7 

3.7. Continuity Studio (2,750 ft 3 ) 9 

3.8. Echo Rooms 9 

3.9. 4th Floor Listening Room 10 

4 CONCLUSIONS 10 

4.1. Sound Insulation ....' 10 

4.2. Acoustics of Talks and General-Purpose Studios . 10 

4.3. Music Studios 10 

5 REFERENCES . 11 

APPENDIX 16 



CONFIDENTIAL 
Report No. B.059 



September 1954 

Serial No. 1954/18 



SOUND INSULATION AND ACOUSTICS 
IN THE BELFAST STUDID CENTRE 



SUMMARY 

During the years 1952/3, all the studios in Broadcasting House, Belfast, 
except Studios Nos. 1 and 4, were given permanent acoustic treatment. This report 
summarises the results of acoustic measurements in all the studios, describes certain 
modifications which were made during the building work, and discusses conclusions of a 
general nature which resulted from the work. 



1. INTRODUCTION. • 

Broadcasting House, Belfast, was completed structurally at about the time of 
the outbreak of war, in 1939, but the studios remained unfinished, the acoustic 
treatment consisting of strips of carpet felt hung from the bare brick walls. In 
1947 Studios Nos. 3, 5 and 8 were given an inexpensive treatment of rockwool covered 
with hessian, in conjunction with linoleum membrane bass absorbers. Acoustic tests 
described in Research Report B.038 , showed that these studios, though improved, were 
too reverberant in the bass and had excessive absorption at middle frequencies. The 
present report describes the new permanent treatment of Studios Nos. 2, 3, 5, 6, 8 and 
the Continuity Studio, carried out in the years 1952 and 1953, and gives the results 
of acoustic measurements in these studios and in No. 1 which has new temporary 
treatment. 

Particular attention was paid to the defects in sound insulation, due to bad 
studio layout, which have been a source of difficulty in operation. Some of these 
defects cannot be overcome without major structural alterations, and their effects can 
therefore be reduced only by careful planning of rehearsal and transmission bookings. 
It is desirable, however, to examine the causes of these faults so that they may be 
avoided in future. 

The building contains one orchestral studio (No. 1), a general— purpose 
studio (No. 8), two smaller drama or music studios (Nos. 3 and 5), two talks studios 
(Nos. 2 and 6) and a continuity studio. Studio No. 4 is an effects studio and store, 
still untreated. There are two echo rooms and an acoustically treated listening room. 
In this report, sound insulation is considered first, followed by details of the 
acoustics of individual studios. Table 1, in the Appendix, summarises the dimensions, 
volumes and locations of the studios. 



2. SOUND INSULATION BETWEEN STUDIOS. 

All the studios except Studio No. 2 are accommodated in one wing of the 
steel-framed building, as indicated in Pig. 1. It is evident from the diagram that 
the possibility of sound leakage exists between Studio No. 8 and Continuity Studio, 
Studio No. 5 and Continuity Studio, Studios Nos. 5 and 3, and between Studio No. 1 and 
the two drama studios Nos. 3 and 5. The effects of long— path transmissions through 
the steel frame have also to be considered. For example, it is found possible to 
hear in Studio No. 1, the sounds of an orchestra playing in Studio No. 8, sound 
transmission taking place through the walls or frame of the building. Impact sounds 
originating on the solid floor of Studio No. 1 can be heard throughout the wing. 

The worst potentialities of this studio lay— out were anticipated in the 
original designs by providing a false ceiling to Studio No. 1, thus reducing trans- 
mission to Studios Nos. 3 and 5, and by building inner shells for the two latter 
studios, isolated from the main structure, to reduce the leakage between them and also 
leakage from the floors above. The Continuity Studio also had a false ceiling to 
avoid leakage from Studio No, 8 above. Nevertheless several minor difficulties arose, 
so that modifications of detail were found necessary as the building progressed. 
This section of the report gives an account of the insulation measurements made in the 
course of the investigation, a summary of the results being given in Table 2 of the 
Appendix. 

2. 1. Insulation Between Studio No. 1 and Adjacent Studios. 

The first measurements of sound insulation were carried out in June 1952 
during the construction of the inner shells of Studios Nos, 3 and 5. It was found 
that there was very considerable leakage from Studio No. 1 into Studios Nos. 3 and 5, 
particularly the former, through the ventilation ducts. A Tannoy "Phonmeter" in 
Studio No. 3 gave scale readings of 65-75 during a rehearsal of the Northern Ireland 
Light Orchestra in Studio No. 1, from which it will be understood that the leakage was 
sufficient for the music to be heard in considerable detail. 

It was found that the leakage occurred through spaces surrounding the 
ducting and through the walls of the ducting itself where this was not lagged. 
Correction of these faults resulted in a considerable improvement, making Studios Nos. 
3 and 5 usablej the subsequent addition of a false ceiling to Studio No.l made 
further improvement and the sound insulation is now considered to be satisfactory. 
The measurements in these last two stages are shown in the first and third columns of 
experimental results in Table 2. 

"Footsteps— machine" noise was measured from Studios Nos. 3 and 5 to Studio 
No. 1, and loudness levels, summed from octave band measurements by the method of 
Mintz and Tyzzer , being 64 and 69 phons* respectively. These figures are outside the 
limit of 58 phons tentatively fixed by Research Department for small studios, but it 
was decided that no building alterations were necessary for the following reasons: 



The phon, as defined by the B,S.L , has no relevance to measurements In the field. In this 
report the unit is used loosely, for want of a practically realisable unit, to mean a single 
figure compounded from a series of o et av e- b and width measurements and related as accurately 
as possible to subjective loudness. 



a. Studio No. 1 would be used mainly for orchestral music, for which a higher 
background noise is acceptable. 

b. The false ceiling was not yet built. 

c. Much of the floor area in Studios Nos. 3 and 5 would be carpeted., 

2.2. Insulation Between Studios Nos. 3 and 5. 

Studios Nos. 3 and 5, lying side by side, are intended as drama studios of 
equal size, Studio No. 3 being acoustically dead, and Studio No. 5 live. Studio No. 5 
is used also for solo musical programmes and small dance bands, and hence good 
insulation is required between the two studios to prevent programmes of this type 
interfering with drama in Studio No. 3. However, the sound insulation between the 

two studios is unsatisfactory, despite their inner-shell construction. The path of 
the leakage could not be ascertained with certainty, but appeared to be through the 
ceilings rather than through the three brick walls separating the studios. No 
improvement could be expected without considerable building work, supplemented by 
further experiments. 

2.3. Insulation of the Continuity Studios. 

The most likely source of interference to the Continuity Studio is Studio 
No. 8, immediately above, which was used mainly for the Northern Ireland Light 
Orchestra before the completion of Studio No. 1. In practice owing to the floating 
floor construction of Studio No. 8 and a 3 ft space above the ceiling of the Continuity 
Studio, insulation is almost adequate. The "footsteps— machine" figure is 61 phons 
and the insulation for airborne sound is better than 45 dB at all frequencies above 
70 c/s. Both types of interference can be heard in the studio, though they are not 
very intrusive over the microphone circuit. 

2.4. Insulation Between the Control Room and Studios Nos. 3 and 5. 

The new control room lies above Studios Nos. 3 and 5, which must, therefore, 
be protected from ordinary impact sounds and airborne sounds at loudspeaker level. 
The airborne sound insulation is adequate, being better than 45 dB at all frequencies 
above- 70 c/s. The footsteps noise, however, was unsatisfactory as found, the loudness 
level being 62 phons. A layer of hardboard on the control room floor reduced this to 
52 phons, from which it was estimated that a Korkoid covering would be satisfactory. 
No measurements have yet been made in the final condition but the impact and airborne 
noise insulation appears to be adequate in service. 

2.5. Insulation of Studios Nos. 2 and 6. 

These studios are more favourably sited than the rest, as they do not lie 
adjacent to any other studios either horizontally or vertically, and it is not 
necessary therefore to resort to arranging bookings in such a manner as to avoid 
inter-studio interference. No insulation measurements were made, though in neither 
case is the insulation completely satisfactory. From a microphone in Studio No. 2 it 
is possible to hear a loudspeaker in the floor below, footsteps in two corridors, a 
compressor-pump outside the building and a piano in a neighbouring practice room. 



Studio No. 6 lies adjacent to a corridor and an attendant has to be stationed 
outside during transmissions to hush staff walking past. 

There is little which can be done about either studio except to reduce the 
interfering noises; acoustic treatment of the vestibule of Studio No. 2 has, however, 
reduced the transmission of footstep noise from the corridor outside. 

2.6. Studio-to-Cubicle Insulation. 

The measurements of insulation between studios and their cubicles are 
tabulated in the Appendix, Table 3. Where further comment in the case of particular 
studios is necessary, it will be included in Section 3 dealing with the acoustics of 
the individual studios. "Howl— round" figures are given in Table 4. 

2.7. Discussion of Inter-Studio Insulation. 

The principal difficulties with regard to sound insulation between the 
studios arises from the layout of the building, all the music studios having common 
boundaries with studios intended for talks or drama. The possible disadvantages of 
the steel frame have been avoided by double-shell construction of the studios where 
necessary. The common boundaries could have been eliminated entirely, however, by a 
different layout of the available space. Interference of one programme by another 
can only be avoided by a complete separation of studios used for music from those used 
for talks or drama. 




Fig.1 

Layout of studios in north wing of B.H.,Beltast. 

(Not to scale) 



3. GENERAL ACOUSTICS. 

The acoustic treatment of the studios follows current B.B. C. practice, using 
membrane absorbers for low frequency absorption and glasswool or rockwool covered with 
perforated hardboard or Tygan fabric. The results of measurements are summarised in 
tables and graphs at the end of the report. The reverberation characteristics of the 
studios are shown in Figs. 2 and 3 and those of the cubicles in Figs. 4 and 5. 

3.1. Studio No. 1 (75,000 ft 3 ) Orchestral Studio. 

This studio is only partly completed. A permanent false ceiling has been 
built, but the walls remain as distempered brickwork and the floor is concrete, partly 
carpeted and having a central square of linoleum. 

The only acoustic treatment consists of some Cabot's quilt and 45 membrane 
absorbers taking the form of boxes closed with linoleum or roofing— felt membranes 
covered with cartridge paper. The reverberation time is shown by Fig. 2(a). 

The optimum reverberation time for a studio of this size is 1°2 sec, and 
the studio consequently sounds rather dead at high frequencies. This will be 

corrected by covering some of the Cabot's quilting with paper and by painting the 
brickwork with Snowcem, a finish which is less porous than distemper. As a temporary 
measure, the loudspeaker circuit in Echo Room B has been given a rising characteristic 
and is used to supplement the high frequency reverberation for certain programmes. 

The listening cubicle to Studio No. 1 is virtually untreated acoustically 
and has too high a reverberation time at low frequencies, Fig. 4(a). Temporary 
measures are being taken to correct this fault. 

3.2. Studio No. 2 (4,000 ft 3 ) Talks Studio. 

Studio No. 2 and its cubicle are formed within two rooms of identical dimen- 
sions, the cubicle being reduced in width to allow space for a vestibule insulating 
both entrances from the corridor. The studio has a ceiling of Colterro lath and 
plaster on wood joists, and additional bass absorption is provided by 3 in. double 
membrane absorbers on the walls and beneath a mahogany shelf running along one side of 
the studio. The remainder of the acoustic treatment consists of 2 in. thick rockwool 
covered with perforated hardboard. The entire floor is covered with a heavy carpet 
absorbing strongly over the entire middle and upper frequency range. 

With this treatment the reverberation curve was found to be not very 
different from the final condition shown in Fig. 2(b); subjectively there was a 
colouration at 90 c/s and there was a lack of middle frequency reverberation compared 
with the rest of the range, the curve falling to 0°25 sec. at 2 kc/s. This condition 
was corrected by replacing some of the 20$ slotted hardboard by imperforated hardboard, 
bringing the 2 kc/s figure up to 0°4 sec. and reducing the low-frequency reverberation 
by about 0° 1 sec. After about a year's experience of the studio in service, however, 
it was felt that the middle and upper frequency reverberation could be reduced with 
advantage. Some of the unperforated hardboard was therefore replaced by Tygan 
fabric. Fig. 2(b) shows the reverberation characteristic for the final condition, 
which is now regarded as satisfactory. 



The ventilation noise level is too high, giving readings of 34r-40 dB on the 
Dawe Sound Level Meter, with a 40 dB A. S.A. weighting network, compared with the 
accepted maximum of 30. 

In the initial state the double observation window was fitted with two panes 
of glass of -| in. and J in. thickness respectively. The studio and cubicle were very 
prone to acoustic feedback resulting in a howl if a high monitoring level was used, 
the maximum permissible gain from the microphone in the studio to a normal listening 
position in the cubicle being only 5 dB for some microphone positions. The frequen- 
cies of howl were found to be 32 c/s or 64 c/s corresponding with the common first and 
second lengthwise modes of the studio and of the cubicle (17-| ft}. It is clear that 
the unusually low stability was due to the fact that pressure maxima occurring in the 
cubicle along the partition wall at 32 c/s and its harmonics were able to excite the 
same modal frequencies in the studio. The window was found to be the principal 
leakage path at -these frequencies and the thicknesses of the two panes were therefore 
increased to -| in. and -| in. respectively. This modification greatly improved the 
howl— round stability, though it did not appreciably affect the average sound insulation 
figure which was already satisfactory. 

Pig. 4(b) shows the reverberation characteristics of the cubicle. 

3.3. Studios Nos, 3 and 5 (6,300, 6,700 ft 3 ) Drama Studios. 

Studios- Hqs.. 3 and 5 will be considered together since they form a pair of 
drama studios and the problems of their design and treatment were in many respects 
similar. They are rather low for their horizontal dimensions, and the original 
designs did not include any absorbing material on the ceilings. Experience with the 
studios in 1 and 1A Portland Place suggested that severe rings and flutters would be 
expected. Ceiling absorbers as used in Portland Place were therefore added, consist- 
ing of glasswool blankets enclosed in Tygan— covered frames, suspended at varying 
distances up to 18 in. from the ceiling. Fig. 6 which is a photograph of Studio No. 5 
shows the appearance of the ceiling absorbers. 

Each studio is built in the form of a complete brick shell isolated from the 
rest of the building by cavities around the walls and ceiling and by a layer of 
glasswool quilt beneath the concrete floor. The ceiling, consisting of Colterro lath 
and plaster, is suspended from the main structure by felt pads, and the inner walls 
stand on two layers of bituminous roof ing- felt . The inner walls were originally 
intended to be of 3 in. clinker block which would have provided a great deal of 
absorption below 250 c/s, but 4-|in. brickwork was substituted in the interests of 
improved insulation. The bass absorption thus lost was difficult to recover and it 
was eventually necessary to increase very considerably the number of low-frequency 
membrane absorbers in each studio. 

When first tested, both studios were excessively reverberant in the bass and 
there was a dip in the reverberation characteristic at 1,000 c/s due to the use of 
slotted (20$ open area) hardboard for covering the porous absorbers on the walls. 

Studio No. 3 has an average reverberation time of 0°4 sec. above 175 c/s and 
is found to be good for drama productions requiring dead acoustics (Fig. 2(c)). It 
is equipped with an effects staircase. The reverberation time of Studio No. 5 



averages 0'52 sec. over the same frequency range (Fig. 2(d)). This value is found 
to he satisfactory for musical programmes, but there are colourations at 130 c/s and 
190 c/s. A sufficient range of acoustic conditions for drama, making use of both 
studios can be obtained by the use of screens. 

The reverberation characteristics of the control cubicles are shown in 
Figs. 4(c) and 4(d). Neither cubicle is good, that of Studio No. 3 being generally 
too reverberant while that of Studio No. 5 is described as "boomy". 

3.4. Studio No. 4 (4,100 ft 3 ) Effects Studio. 

This studio still has a temporary treatment of carpet felt hung on the bare 
brick walls. It is used as an effects store and no tests were made. 

3.5. Studio No. 6 (1,550 ft 3 ) Talks Studio. 

Studio No. 6 intended for use as a recording studio, has the longer walls 
parallel and the shorter walls inclined at an angle of about 3° to each other. Its 
cubicle is similarly shaped but narrower in plan. The acoustic treatment of the 
studio has no unusual features. 

There are colourations at 150 c/s and 430 c/s but speech quality is never- 
theless fairly satisfactory. The reverberation curve is shown in Fig. 3(a). Listen- 
ing tests were made more difficult by a ring in the cubicle at about 165 c/s cau"- a T 
the sheet metal casing of the Marconi control desk. A ribbon microphone is used with 
slight bass correction to reduce the effect of excessive reverberation below 120 c/s. 
Sound insulation to the cubicle is just adequate and though the "hovl-round" figure is 
not good, no trouble has been experienced. 

The cubicle is boomy, the reverberation cur/e (Fig. 5(a)) rising steeply in 
the bass. 

3.6. Studio No. 8 (30,000 ft 3 ) General Purpose Studio. 

In its original state, as described in Research Report B.038, this studio 
was characterised by excessive bass reverberation and by extreme deadness m the 
region of 500-1,000 c/s. In 1950 a wood strip floor, was laid and there was a 
noticeable improvement. The middle frequency region still remained dead, however, 
owing to the action of the linoleum membrane absorbers which forced a dado round the 
studio. At the beginning of 1952 the permanent re-treatment of the studio was 
finished; a polished wood reflector covered a large central are>a of the wall behind 
the orchestra and sufficient absorption to bring the mean reverberation time to 
1-2 sec. was dispersed about the walls and ceiling. Fig. 7 shows the reverberation 
characteristics measured in the course of these changes. Fig. 7 U) is the original 
curve measured in 1948, and Fig. 7(b) is an estimated curve after the wood strip floor 
had been laid. Fig. 7(c) was measured by S. S.E.H. S.B. ' s department in April 195^, 
after the permanent treatment had been completed. In this condition, the studio was 
considered to be too reverberant for normal use with the Northern Ireland Light 
Orchestra and further modifications were made. Additional absorbing materials were 
fixed to the ceiling and the reflector was slotted and backed with rockwool to prevent 
unwanted reinforcement of the tympani and brass. Fig. 7(d) shows the reverberation 



characteristic thus obtained; the mean time is about 09 sec;, and although this is 
approximately equal to the previously accepted B.B.C. optimum time, the studio was now 
rather too dead for a satisfactory distant microphone balance, The definition had 
been improved, however, and colourations previously present had been eliminated. A 
further slight adjustment was made to lift the reverberation time in the region of 
1,000 c/s, glass fibre being removed from behind slotted hardboard panels over a total 
area of 100 ft 2 . This change resulted in an appreciable improvement, though the 
studio remains rather too dead for music. The placing of bass instruments is very 
critical and definition is poor with a single microphone. The results obtained with 
drama and with the multi-microphone balances normally used by the N.I.L.O. are 
acceptable. 

Fig. 7(e) is an estimated reverberation curve for the final condition. The 
experiments confirm previous experience in showing that the achievement of good 
definition and balance with an orchestra of 25 players in a studio as small as 
30,000 ft 3 may be difficult if an adequate reverberation time for good tone quality is 
to be preserved. Better results are obtained from Studio No. 1 with its volume of 
75,000 ft?, even though it has received only rudimentary acoustic treatment. It 
would not be true to say, however, that the small size is the only reason for the poor 
compromise between tone quality and definition; Glasgow Studio No. 2, for example, is 
smaller and gives better results. The table below compares the volumes and reverbera- 
tion times of the smaller regional music studios: 

Studios used for orchestras up to about 30 players 



Studio 


Approx. No, 
of players 


Volume 

ft 3 


Mean Reverberation Time 


Empty 


With Orchestra 


Glasgow No. 2 


24 


24,000 


0-99 


0=82 


Belfast No. 8 


25 


30,000 


0=91 


0°79 


Manchester No. 1 


20-25 


33,000 


1-10 


0=99 


Swansea No. 1 


32 


36,000 


1°27 


1=01 


Charles St. , Cardiff 


32 


43,000 


1=38 


1=10 


Bristol No. 1 


30 


58,000 


97 


0=87 



It will be seen tliat Belfast Studio No, 8 has a lower mean reverberation 
time than any other, including even Glasgow Studio No. 2 which has only four-fifths of 
the volume of Belfast Studio No. 8. Reference to curves (c), (d) and (el of Pig. 7 
shows that apart from two fluctuations the reverberation time falls as the frequency 
rises, in contrast to the behaviour of many other studios. The additional absorption 
by the orchestra will increase the rate of fall. 



An analysis of other small-orchestra studios, which will not be given in 
detail here, suggests that the mean reverberation time from 1,000 c/s to 4,000 c/s 
with the orchestra present should be at least as great as that from 125 c/s to 500 c/s. 
This conclusion may not apply to large studios, in which a relatively longer middle 
frequency reverberation time is found to be acceptable, but it appears to be particu- 
larly applicable to studios less than 60,000 ft 3 in volume. 



In the case of Belfast Studio No. 8 the mean reverberation times in the lower 
and upper bands are respectively 0°87 sec. and 0°71 sec, a fall of 2056. It appears 
probable therefore that the definition and tone might be improved by increasing the 
reverberation time above 700 c/s to about 0°95 sec. with the orchestra in the studio. 
.It must be remembered, however, that the studio will not be used primarily for 
orchestral programmes, and such a change would not improve the studio for other 
purposes. 

The cubicle has the same basic treatment as in 1948, but has been modified 
to reduce the upper frequency reverberation (Pig. 5(b)). It is considered to be 
satisfactory. 

3.7. Continuity Studio (2,750 ft 3 }. 

The Continuity Studio is of generous sizej it has an inner lining of 3 in. 
breeze with a 2 in. cavity, standing on isolating layers of bituminous felt. The 
floor, consisting of | in, boarding on 1-| in. battens, lies on a layer of quilted 
glass wool. The Colterro lath ceiling is suspended in the same manner as that of 
Studios Nos. 3 and 5. The acoustic treatment consisted initially of 1 in. and 2 in. 
deep porous absorbers covered with slotted hardboard of 2056 open area, and suspended 
frames of Tygan-eovered glasswool as in Studios Nos. 3 and 5. The reverberation 
characteristic was found to be too high in the bass and too low in the 1,000 c/s 
region. The anti-flutter ceiling absorbers were therefore replaced by membrane 
absorbers and some of the £D% hardboard covers by unperforated hardboard or Tygan 
fabric. 

When this had been done, the shape of the reverberation characteristic was 
satisfactory, but the mean reverberation time of 0°51 sec. was found to be too great. 
Further modifications reduced the mean time to 0°40 sec, though the characteristic 
(Fig. 3(d)) falls steadily with increase of frequency and the studio remains rather 
boomy and coloured in the bass. 

There is no control cubicle, the studio being monitored from a desk in the 
adjacent control room. The insulation between the studio and the control room is 
satisfactory and the monitoring desk area is partly enclosed for protection against 
control room sounds by a screen and roof of Tentest "Rabbit-Warren" board. 

3.8. Echo Rooms. 

There are two echo rooms. Echo Room A is on the 3rd floor, lying adjacent 
to the cubicle of Studio No. 5. Echo Room B is on the fifth floor and is normally 
associated with Studio No. 8. Though identical in size with Echo Room A, it differs 
in having a dividing wall along the centre line extending from one end of the room to 
within 5 ft of the other end. The LSU 10 loudspeaker and the microphone are placed 
on different sides of the dividing wall, well away from the communicating end. 

The reverberation characteristics are shown in Figs. 8(a) and (b ) . That of 
Echo Room A, which has no deliberate acoustic treatment, falls from 2^ sec in the bass 
to 0°8 sec. at 8,000 c/s. Echo Room B has been acoustically treated with membrane 
absorbers, and the reverberation time reaches its highest value of 2° 2 sec. between 
700 and 2,000 c/s. It is found to be very suitable for use in conjunction with an 



10 

orchestra in Studio No. 1, for which purpose, a filter with a rising frequency- 
characteristic is sometimes inserted into the loudspeaker circuit. 

3.9. 4th Floor Listening Room. 

A quality checking room is situated on the 4th floor next to the Continuity 
Studio. The acoustic treatment consists of shallow porous absorbers, the only bass 
absorption being provided by the plaster and Colterro lath ceiling. The reverberation 
characteristic is shown in Fig. 8(c). 



4. CONCLUSIONS. 

Some conclusions of a general nature were .formed as a result of the 
experimental work described above. They are stated briefly here as a guide for 
future designs. 

4. 1. Sound Insulation. 

It is not practicable to put a music studio adjacent to any other studio 
without providing complete isolation, e.g. by an open corridor or some equally large 
cavity. Impact sound insulation is satisfactorily dealt with by the floating floor 
constructions used in Belfast. 

The double windows between studios and their cubicles should have glass of 

thickness not less than - in. and - in. to avoid the possibility of "howl-round". 

8 2 * * 

The dimensions of cubicles and studios should not be identical, nor in simple ratios, 
especially perpendicular to the common window. 

4.2. Acoustics of Talks and General— Purpose Studios. 

The three Belfast studios intended for speech are only fairly good. The 
reverberation times all decrease from about 0°45 sec. at 100 c/s to 0*3 sec. at 
8,000 c/s, but they are acceptable with suitable microphone corrections. Experience 
with these studios in their intermediate and final stages confirms other experience in 
showing that the reverberation time should not start to rise with decreasing frequency 
until a frequency lower than 100 c/s is reached. Excessive reverberation between 
100 c/s and 200 c/s gives rise to very serious colourations. 

Breaking up of the ceiling areas by the use of suspended absorbing frames 
was successful in eliminating flutters and rings, but absorbers of a similar area 
forming part of the ceiling would probably have been equally effective. 

Slotted hardboard of 20$ open area cannot be regarded as an effectively 
transparent cover for porous absorbers. Alternative types of cover, e.g. Tygan 
fabric, have been found necessary to provide adequate absorption above 2,000 c/s. 

4.3. Music Studios. 

In the design or re-treatment of small music studios it is necessary to 
ensure that with the orchestra in the studio there is no general decrease of reverbera— 



11 

tion time with increasing frequency. The mean reverberation time between 1,000 c/s 
and 4,000 c/s under these conditions should be at least as great as that between 
125 c/s and 500 c/s. To achieve this object, the reverberation characteristic of the 
empty studio should be a maximum in the former frequency range. 



REFERENCES. 

1. Research Department Report B.038, "Acoustic Measurements in Belfast Studios", 
January 1349. 

2. Mintz and Tyzzer, "A Loudness Chart for Octave Band Data on Complex Sounds", 
J. A. S.A. 24 (January 1952), pp. 80-83. 

3. Research Department Technical Memorandum B.1004, "The Acoustics of the 
Studios at 1 and 1A Portland Place", November 1952. 



12 



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6 
5 
0-4 
0-3 
0-2 
0-1 




(a) Studio No.1 (75,OOOcu.ft.) (b") Studio No. 2 (4,000 cu.ft.) 
(c) Studio No.3 (6,30Ocu.ft.) (d) Studio No.5 (6,700 cu.tt.) 



± 



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| o 
§ ° 

o 



Z 



Fig. 2 — Reverberation characteristics ot studios. 




(a) Studio No.6 (1,550 cu.tt.) (b) Studio No.8 (30,000 cu.ft) itloor carpeted.J_ 

(c) Studio No.8 (30,OOOcu.ft. no carpet.(d)Continuity (2,750 cu.ft.) 

I I I I I I I I I I I i I I I I I I I I I I 



O O O O ' 



3 OOOoOOO° o O 

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Frequency in cycles per second 
Fig.S-Reverberation characteristics af studios. 



"to o o © © " 
o o o o o 

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13 



l-l 
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(a) Cubicle to studio No.l (b) Cubicle to studio No. 2 














(c) 


Cubicle 


to s 


tudi 


o h 


lo.3 (d) Cubicle 

I I 1 1 


to studio No 

1 


5 









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Fig.4-Reverberotion characteristics of listening cubicles. 





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Frequency in cycles per second 
Fig.5~Reverberation characteristics of listening cubicles 



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14 




Fig. 6 - Photograph of Studio No. 5 showing absorbers 
suspended from ceiling to prevent flutters. 



15 



2-4 



2-2 



2-0 



1-8 



1-6 



1-4 



1-2 



? I -0 



*> 0-8 



0-6 



0-4 



0-2 




(a)Temporary treatment November 1948. (b")After laying of wood strip floor (estimated), 

-(c)Permanent treatment April 1952 (no carpet). (d)First modification March 1953. 
I I | I | I I (e) Second modification (estimated). I 

_J I I I I _J I I I _l I i l l , J I 1_ 



Fig.7 Reverberation characteristics of studio No.8 



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(a) Ec 

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to room, 3>"d. -floor, (b) Echo room, 5 

ii i i i i i i i i 


th. floor, (c) Listening room 4 tn -floor. 

ii i i i i i I i i 



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Fig.8-Reverberation characteristics. 



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16 



APPENDIX 
SUMMARY OP MEASUREMENTS 

Table 1 
Dimensions of Studios etc. 





Floor 


Dimensions 


Volume 
ft 3 


Notes 


Studio No. 1 


Ground 


60 x 43! 


x 29 


75,000 


(Temporary 


Cubicle No. 1 


Ground 


11 x 10 


x 10 


1,100 


J treatment 


Studio No. 2 


1st 


22 x 17| 


x 10 


4,000 




Cubicle No. 2 


1st 


18 x 16 


x 11 


3,100 




Studio No. 3 


■ 2nd 


28 x 20| 


x 11 


6,300 




Cubicle No. 3 


2nd 


15 x 14 


x 10 


2,100 




Studio No. 4 


2nd 


22 x 14 


x 14 


4,100 


( shell only ) 


Studio No. 5 


2nd 


29 x21| 


x 11 


6,700 




Cubicle No. 5 


2nd 


16 x 13| 


x 10 


2,130 




Studio No. 6 


4th 


15 x 12 


x 84 


1,550 


Non- parallel walls 


Cubicle No. 6 


4th 


17 x 84 


x 104 


1, 360 




Studio No. 8 


5th 


49| x 29| 


x 23 


30,000 




Cubicle No. 8 


5th 


20§x 13! 


x 10 


2,930 




Continuity 


4th 


20 x 12! 


x 11 


2,750 




Listening Room 


4th 


14! x 13 


x 11 


?;,070 




Echo Room A 


3rd 


16 xl4 


x 11 


2,620 




Echo Room B 


5th 


15! x 15 


x 11 


2,610 


With dividing wall 



Table 2 
Measurements of Airborne Sound Insulation between Studios 









Studio 


Nos. 




Prom 


1 


1 


3 3 


C.R. 


8 


To 


3 


5 


1 5 


3 


Continuity 


c/s 






Insulation 
* 


dB 




44 


- 


— 


39 24 


— 


- 


50 


- 


- 


48 36 


62 


20 


62 


36 


39 


41 31 


40 


38 


75 


- 




34 37 


48 


50 


88 


41 


40 


38 30 


45 


45 


105 


- 




32 32 


50 


46 


125 


48 


45 


44 35 


46 


41 


150 


- 


- 


36 


50 


- 


175 


50 


51 


45 41 


54 


47 


2lO 


_ 


- 


50 


57 


- 


250 


59 


64 


49 50 


52 


48 


350 


69 


69 


51 50 


60 


51 


500 






57 55 


56 


63 


700 






62 61 




65 


1,000 






64 65 






1,400 






64 71 






2,000 













Before construction of the ceiling in Studio Ho, 1 B 



17 



Table 3 
Sound Insulation between Studios and Cubicles 



Studios Nos. 


2 


3 


5 6 


8 


Continuity 


Frequency 






Insulation 


dB 




c/s 












44 


44 


43 


41 


- 


22 


50 


42 


33 


39 


•43 


32 


62 


40 


35 


52 32 


41 


34 


75 


40 


53 


45 


39 


29 


88 


53 


50 


53 21 


43 


38 


105 


43 


49 


43 


42 


31 


125 


40 


45 


46 33 


52 


32 


150 


45 


54 


- 


43 


36 


175 


42 


41 


50 32 


49 


39 


210 


- 


46 


— 


- 


38 


250 


47 


49 


47 35 


49 


42 


350 


50 


50 


50 37 


48 


46 


500 


53 


51 


56 48 


47 


49 


700 


58 


55 


64 47 


58 


53 


1,000 


64 


54 


64 54 


56 


51 


1,400 


64 


51 


62 51 


56 


- 


2,000 


60 


51 


54 49 


55 


- 


2,800 


59 


- 


58 46 


58 


- 


4,000 


66 


- 


62 47 


59 


~ 



Table 4 

Howl— round between Studios and Cubicles (Pinal Condition) 

The figures in this table represent the maximum sound— level gain in dB 
between a microphone in the studio and the normal listening position in 
the control cubicle, above which howl—round occurs . The experimental 
chain comprises the microphone and monitoring loud— speaker normally used 
with the studio. 



Studio 


Howl-round gain (dB ) 


Best mic. position 


Worst mic. position 


No. 2 


22 


18 


No. 3 


32 


32 


No. 5 


32 


32 


No. 6 


30 


24 


No. 8 


32 


32 


Continuity 


30 


26