RESEARCH
DEPARTI~~~
THE RDBUILDING OF THE SrI'UDIO PREMISES
IN ALEXAl~DRA ROAD, SWA1~SEA
Report No. B.052
Serial No. 1952/20 ,
Inves tiga ti0l!..j?~)
C.L.S. Gilford
M.W.
A.IJ.
K.E.
]'.L.
Greenway
Newman
Randall
Ward
F.L. Ward
/ r-v-..::;l
/
.tf
Fe
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,/'./
~'';''''-'7 /'1"" /.::'C:t'--..J
(W. ProctorWilson)
PRIVATE AND CONFIDENTIAL
Researoh Department
October, 1952
Figs. l\fos.
- B.052.10
B.052~1
STJ.MMA.RY
In ?8building the Swansea Studio Centre it was decided to use
Relmholtz Resonators for low-frequency sound absorption in
Studio 1.
This report describes the work done in this
connection by Re8earoh Department, oomprising preliminary
design and laboratory measurement of the resonators, and
stage-by-stage measurements during the construction of the
studio.
This is the first occasinn on which Helmholtz
Resonators have been used in this country for bass absorption9
their disposition in linearrays, which possesf3es advantages
over other arrangements', has not so far as is known been
previously used.
The results 6facoJ.l.stic measurements in
the other three studios are also given.
1.
•
INTRODU5TION
At Swansea the B.B.C. Studio Centr0 9 whioh was destroyed by fir(3
during the war, has recently been rebuilt.
The Centre has four
studios, three on the tirst floor, and the f~urth on the second floor.
Of these, No. I is a Music Studio of 1,200 m (36,000 ft 3 ) volume,
two fbors in height, to which is attached a Narr~tor' s Studio "vi th
an irregular five-sided plan and a volume of ~O m.
No. 2 is a
General-Purpose Studio with a volume of 190 m 9 and No. 3 ;)n the
second floor is a Talks Studi~ rather larger than the Narrator's
Studio.
The control cubicle of No. 1 has a second window overlooking
Studio 2, which has its ovm control cubicle at the opposite end.
Single pairs of doors open from both Studios 1 and 2 on to the
central corridor, but the direct transmissi~n of sound between~them
is reduced by a pair of doors across the oorridor between them."
Theoontrol room is situated on the second floor above Studio 2 •
. This report describes laboratory and field work done by Research
Department in connection with tho rebuilding of the Centre.
It was deoided to use low-frequency absorbers of the R6lmholtz
resonator type in the largest of the studios (Studio No~l).
-2A special study of absorbers of this kind has already been made and as
this ·was the first occasion on which these had been used in this
country 1 reverberation time measurements were carried out in the studio
at intervals durinb the building.
.
The report is divided into four main sections.
In the first the
problems involved in the design of the resonators used in Studio No. I
are discussed briefly.
Secondly the laboratory measu,rements on the
resonators are summarised.
Field measurements made whilst the large
studio was being built are then described 1 followed by a reference to
the measurements made on all of the studios in the Centre after completion.
2.
l1J..YJDSTIGATIONS ON THE HELMlI01'.PZ AJ3S0RJFdl.§.
The olf1+¥ work_ on resonators previously report.ed by. Research
Departtnent \ ~) was on' lov~ frequency resonators arranged in plane
arrays; these arrays offer some advantages over isolated resonators?
notably in that they can be arranged to have a low Q factor and yet
still possess a high absorption coefficient.
The B~B.C. Building Department 9 however 9 suggested that both
aesthetic requirements and the need to introduce as much diffusion
as possible would-be better met by resonators projecting from the
wall surface· and grouped in single straight rows.
This arrangement
which will be re:(erred .toas the line-array has oharacteristics
intermediate between those of the isolated resonator and of the plane
a~ray discussed in Report B.041~
The design of resonators of this form-to give a desired
resonanoe frequency presents little difficultY9 but there are
difficul ties in computing the amount of abf;lo.rption that they will
introduce into a room.
The performance of an absorber of normal type is expressed as
an absorption coefficient defined as tho.fractiop of incident sound
energy which is absorbed, but the absorption of a single Helmhol tz.
resonator· cannot be so expres.sed sinoe . it is uo.t olear over what
a:rea it may be.oo:p.sidered to be aoting.
It is therefore oonvenient to express the absorption as the area of perfeot absorber
required to produce the same result.
'J:1he maximum absorptio.n at
J.·esonanoe Am? is obtained when the frictional resistance present
in the reso~ator itself is equal to the radiation resistanoe of the
- 3resonator.
The olassica1 value for the latter is given by
R
r
Dimens~ons
where
~ '" density of air
A, '" wavelength of the sound
f ~ frequency of the sound
c '" velocity of "sound in air.
lifow it can be shovm (ii) that the maximum absorption associatod
with a resonator is given by
and hence in this case
A,2
Am '" 2 '!l'
(2 )
The equivalent figure fora single- resonator of a plane array
is given by
R
r '"
...f..£
S
where S is the area of
the plane associated wit~
each resonator
and the maximum attainable absorption is S.
This is equivalent to
saying that the absorption coefficient is unity in this case.
The value of radiation resistance used for the line arrays is
given by
where d is the distance
between necks 7
and the maximum absorption is given by
- 4The thr~e cases are compared in '1'able (1)
rrABLE.· (1)
RAPJATION RES@rAN,..9!.llIfD l'vTAXIMUM ABSORPTION:
OF IIELMH01'L'Z RESONATORS '
-'
--------~--.--
----------.-.---Radiation Resistance
Absorption Units
per Resonator
----.-
.-----------~---'---~- ..
Single Resonators
-~-----.,---,,--'---.--------.---------.----'--
Plane Array
I
S
S
,-------~-.---~---.-,
,
(")
(ii)
As has ,been discussed elsewhere ~ 9
the-absorption due to the
resonators will be partially cancelled out by the re-radiation of
energy from the resonators during the decay of thesound'9 the effect
being equivalent to the addition of volume to'the room.
With low
values of, the Q factor, however this effect is small? so that a low Q, is
desirable if consistent with other requirements.
The quantity Q here
referred to is defined in the same way as in an electrical circuit?
namely as the ratio of the reactive component of the impedance to the
resistive component.
2.3
T~~J:e,sign
.2..:t: line:E'l'ay resonators for Swansea Studio
~
In Swansea the low frequency resonators were required to absorb
over a band of frequencies from about GO cls to 250 cls and S09 to
allow for adjustment of the shape of the absorption curve 9 resonators
with relatively sharp resonance curves and with several resonance frequencies spread over this band wero 6hos~n in preference to broad-band
resonators.
It has been stated above that the maximum absorption is obtained
when the internal resistanco of the resonator is equal to the
radiation resistance.
If however resonators of several different
frequencies are used to cover a wide band 9 increase of resistance
beyond the matching valuo does not reduce the overall absorption? \
because the decrease in the peak absorption of each resonator is
compens,ated by an increase in band-width with the result that each
\
- 5reson~tor
now absorbs more energy in neighbouring freQuency bands.
A desired absorption/freQuency curve could be achiev~d by the use
of r\'lsonators of widely differing dimensions~
The optimum size for
each fre~uency band was therefore chosen as a compromise between
several considerations.
Among the most impor~ant of these were the
sharpness of the resonance curve ~ the suitability for creating diffus'ion
in the·room? and ease of manufacture.
It was considered advisable to
aim for characteristics similar to those possessed by the resonators
already used in Research Department experiments.
Two basic sizes of resonator were chesen to cover the low
freQuen0Y region 9 different freQuencies b\3ing obtained by the use
ot alterations to the neok dimensions.
Tho fact that all the
resonators would not war];: eQually efficiently under these conditions
was accepted as it enabled the number of types of resonator to be
roduced.
Table (2) below shows the computed information given to
Building Department for the original calculation of the number of
resonators reQuired in the studio.
Although the absorption produced 9Y pl~~~ arrays has been found
to be in reasonable accord with theory\~)9 \~~) ttere was some evidence
at the time of the design of the resonators for Swansea to suggest that
single reson~~9;'~ did not absorb as efficiently as indicated by eQuation
(2).
Bruel\~~~) has given an experimental figure of
'A 2
3.1
'If
A2 .
for the maximum attainable absorption instead of
21f •
SubseQuent experiments have confirmed that under reverber~tion room
conditions at any rate the latter is not attained.
As it was
intended to make laboratory measurements on prototype resonetors before
any were installed in _the studio 9 the theoretical values were assumed
as a Rtarting point in the original design calculations.
As a conservative estimato it was assumed that the absorption
contribution of each type of resonator at the resonance froquencies of
other types should bo ignored? i.e. that the absorption of each type
droppod to zero at the resonance freQuency of thoso next below and
above.
- 6 TABLE (2) CALCULAT~D AB~~~~ION FIGURES FOR
LINE-ARRAJS OF_, RES..9lrliTOR_~J\.S ,US~'p'_ IN SWANSEA
'--,
~--
r
V
..e.
cm.,
cm 3
cm.
.
.
-----~---"-------~----f
clg
d
cm.
D
cm.
U
m3
A2
cm
..
100
0.95
1.10
3900
15
137
75
2.20
0.96
3900
15
182'
200
0·95
0.79
640
10
140
2·54
0.71
640
10
...-._-_.-
10
1860
0.37
8
1500
0.25
67
10
610
0.076
97
9,
460
0.057
----whero j
f,
Resonanoe frequency
~o = Length of nook
r = Radius of nook
V
Volume of oavity
d = Spaoing of neoks along the unit
D = Minimum spacing distance between unns 2f
Q ="Magnifioation" of resonant, system
--2.
where5f is
Bf
A
U
2.4
width of resonance curve at 45% of peJ.k absorption
Absorption (in sq. cm. of perfect absorber),
Additional volull'e'effectively introduced into the room
by each resonator.
The mJEimum spacing between line-arra,;y:s
The min:tmum spacing distance between units is thatneoessary to
divide the wall area into zones each containing one unit and of area
equal to the total absorption given by one unit, i.e. to produce 100%
absorption over the wall surface.
Trere should however be no
objection to placing resonators working at one fre~uency between
those tuned to any other frequenc;r je\¥en if the latter are spaced
at their minimum distance.
3.
LABOR1TORY MEASUREMENTS
For reasons of economy it was decided to make laboratory tests
on the ,largest type of resonator only.
As originally designed by
Building Department 9 the units were hollow plaster castings with no
e
- 7backs.
It was i'ntended to attach them to the walls using a thin
plaster as adhesive, the wall itself forming the back of the cavity.
Experiments were started with this type of resonator? but since
the fixh.g was found difficult plasterboard baoks were eventually
fitted so that the units could be moved easily to different positions
in the reverberation room.
The plasterboard baoks were also adopted
for thestudi0 9 since they provided a better seal between the separate
resonators in the unit.
J.i'ig. 1 shows ·one of the units.
The hollow
rectangular plaster casting is divided by irternal partitions into
eight equal cavities.
Circular holes in the front of the unit
communica~e·with the cavities? the interior of the holes being lined" .
with cardboard tubes of internal diameter I" and length 3/8" (9.5 mm.).
Additional cardboard tubes fitting inside the fixed tubes enable the
diameters and lengths of the necks to be varied? and pieces of fabric
may be stretched a~oss the ends of the removable tubes before
insertion so that they remain 0lamped between the"fixed and removable
tU0es? thus forming an adjustable neck resistance.
3.2
Reverberation room
measurell!.~.nts
The first absorption measurements, made in the large reverb~ration
room in Nightingale Square on twelve units of eight resonators tuned to
100 c/s? showed that the absorption produced was not as great as that
predicted.
Measurements were made under a large number of~conditions
to find those most favourable to high absorption; the positions of the
units in the room were changed 9 a smaller reverberation room was tried
and both warble tone and pure tone tests were made.
In all cases the
frictional resistance was varied until opt~mum absorption conditions
were attained.
These and other experiments showed thatg(1)
The maximum absorption of the resonators was· only about one
third of that predicted.
(2)
The neck resistance needed for maximum absorption was about
three times the calculated radiation resistance.
These facts are consistent with the hypothesis that the radiation
resistance was greater under the measurement condition than the
classical theoretical value.
This effect is being investigated
independently, especially to find out whether the aotion of the·
resonators in small rooms is ilifferent from that in large ones.
It had been hoped to carry out detailed experiments on the
resonators during installa~ion in Swansea? but as faoilities for this
work wero not provided it was decided to use a neck resistance material
- 8 similar to that which gave optimum results in the reverberation room
experiments.
The existence of strong standing waVe patterns in the reverberation
room would tend to raise the effective radiation resistance, and it was
therefore to be eXpected that the latter would tend to be small~r in the
studio conditions.
This being so the neck resistance would be greater
than that required for matching to the studio, but as shown above this
would not materially affect the overall bass absorption since the
bandwidths would be correspondingly increased.
Fig. 2 shows the ab~orption curves of three groups of resonators as
measured in the reverberation room.
Curve 2(a) refers to the 100 c/s
resonato!' of Table (2),while curve 2(b) is that of the 15 c/s resonator
produced by inserting additional cardboard tubes into the necks.
Curve 2( c) is produced by a resonator not listed in, the 'lIable, in which
the fixed cardboard tubes were completely removed from the necks,
raising the resonance frequency to 115 c/s.
The curves all refer tf) effective absorption under, the conditions
of the particular room, but the point A gives the corrected maximum
absorption for curve 2(a) when the theoretical effective increase of-roo~
volume due to energy storage in the resonators is t~.kEm into account.
3.3 Final form of
thelow-frequen~ reson~tor~
The line-array resonators finally used in the studio' differed
in three respects from the resonators as originally desig~edl-
{l)
rrhefrictional damping was greater.,
(2 )
The dimensions of two of the neck inserts were altered to givo
resonance frequencies of 110 c/s instead of 100 c/s, and
150 c/s instead of 140 c/s. "
(3)
The 1mits were made, with plastey backs which projected suffiCiently to provide a fixing flange.
Laboratory'tests were also carried out on perforated-panel
absorbers inteEded to cover the lower-middle fretluoncy region above
250 c/f!..
The panels consi,sted of 8 mm. thick plasterboard with
6 mm. diameter holes at 16 mm.' centres, and were mounted on battens
3 11 from the wall.
Absorbent material oould be inserted into the
cavities formed by the panel and the battens.
~
- 9 Fig. 3 shovJs the absorption curves produced with three types of
backing.
With no backing material the curve is very flat? showing
only a slight peak; with added resistance in the form of scrim behind
the panel the peak becomes 'more pronounced, and a resonance curve with
peak abso:i:'ption of nearly 100% occurs when bitumen-bonded fibreglass
wool is used in place'of the scrim.
Although the holes all communicate with a oommon cavity, the unit
ma;y be considered as a group of small Helmhol tz resonators.
Wi th this
assumption the caloulated resonance frequency is 600 c/s 9 a value which9
as will be seen from the curves, agrEles quite well with the experimontal
peak absor'r)tion frequencies.
The units were actually used in Swansea with a backing fabric
having a resistance similar to two layers of the sorim.
The measurements of D.C~ flow resistance mad,Q in this connection are described in
the Appendix.
4~
FIELD
l'vmASUllEl'vm~S
During the reconstruction 'of the studios four visits were paid to
Studio No: 1.
~nall of these visits reverberation time measurements
were made.
Pulsed glide reoords were also taken, but these will not
be oonsidered in detail here since serious low-frequency faults? for
the detection of which they are at present most valuable, were
fortunately absont.
The first visit was made on 27th December 1951.
The reverberation
time curve taken at this time is shown in Fig. 4(a).
The condition of
the stUdio is shown in the photograph? Fig. 5(a), the general structure
of the studio being completed, including the floor and ceiling.
The
walls had only a rough plaster coat &nd doorways were temporarily closed
for the tests with building bC'ard.
As will be seen from the photograph
a good deal of building material was piled on the floor and there was a
considerable amount of steel scaffolding with wooden scaffold boards.
On the second visit during the 17th and 18th January 1952, the
studio was in a similar condition except that plaste:rboard panel units
had been add.ed to the walls.
The reverberation curVe was measured in
this oondi tion, Fig. 4(b) 9 and during the';lext day 280 resonators tuned
to 110 c/s, and 1,550 resonators tuned to 200 c/s, were laid on'the
studio floor.
This condition is shown in the photograph, 'Fig. 5(b),
and the corresponding reverberation time curve in Fig. 4(c).
- la It will be seen that there is a pronounced reduction of reverberation time in the freQuency region covered by the resonators.
The amount of absorption introduced by the resonators will be
discussed later.
The difference in reverberation time between
these last two cO~ldi tions in the region above 500 c/s is somewhat
disturbing as the introduction of the resonators should have had
little effect in this region.
It is possible however that the
discrepancy was due to a rearrangoment of the scaffolding which was
exhibiting pronounced resonances.
Fig. 6 is a reproduction of a section of two pulsed glide
-records taken on 17th and 18th January respectively; the pronounced change in slope of the decays in the 100 - 250 c/s
region can be seen.
The studio was again tested on Ilth,and 12th February with the
resonators mounted in their correct po~d tions on the wall.
During
this period the cardboard inserts were introduced into the 75 c/s
and 150 c/s resonators.
The photograph of Fig. 5(c) was taken
during this process.
The 75 c/s and 150 c/s, resonators can be
identified by the protruding necks~ and'the perforated plasterboard units can be seen on the far wall.
The reverberation curve (Fig. 4(d)) taken after completion of
this work is appreCiably lower througnout the whole freQuency range
than that of the preceding conditions. ,vVhile this can be accounted
for in the 62 - 500 c/s region by the presence of the additional
rosonators 9 their effect at' higher freQuencits can only be negligible
and it was realised that other changes must have taken place between
the two conditions.
I
With the resonators installed 9 the reverberation time in the
150 c/s region was much lower than that required.
The reverberation
time curVA of 27th December 9 Fig. 4(a)9 also shows a dip in the curve
in this region before any treatment was introduced and it is therefore
evident that the additioJal absorptio~ is due to structure vibration.
The absorption at this freQuency was reduced by blocking up'a
suitable number of resonator holes.
An. estimate of the number of
resonators to be stoppeti. in order to raise the reverberation time at
150 c/s to 1:2 seconds was made by Research Department; using the
reverberation curves of l8tn January and 12th February.
Table (3) shows the number ~f resonators present in the studio
on the 12th February and the number of resonators stopped.
- 11 -
75 cls
Total number
Number stopped
._-_.__.•._---
no
cls
150
300
50
150
'50 cls
200 cls
740
---.-.-----~-.------.-.----
The fourth visit w~s made on 8th'April 1952 when this correction
had been applied.
At this stage also about three-quarters of the
scaffolding had been removed, the "walls and ceiling had been completely
painted and doors had been fiited.
There were some rostra piled in
the studio, but no carpet.
Fig. 4(e) shows the reverberation time
under this condition; it will be seen that the reverberation time in
the 150
region has increased although not to the required extent.
The most noticeable feature however is the very' pronounced increase in
r~verberation time in the high-frequency region.
cls
The pronounced changes in reverberation time over the whole
frequency range considered cannot be assigned to any definite cause,
bui they were probably associ~ted with the presence"of the scaffolding
and with th,e drying out of the new plaster surfaces.
From whatever
their origin 9 however 9 these changes make reliable estimates of the
effect due to the resonators di1'ficul t.
The only really reliable
comparison that can be made is ~etween the conditions of the 17th and
18th January, when substantially the only change in the condition of '
the studio was the introduction of the 110
and 200
resonators.
The agreement between thq predicted values and those derived from'th~
xeverberation predicted curves on those two dates is shown in Fig. 7.
cls
cls
The predicted values were obtained from the original figures given
in Table (2)9 corrected for the absorption material actually used in
the studio.
4.3
Tests on the completed studio
A final visit was paid to the studio centre between 29th April
and 1st May 19529 when the studios had been completed.
The photograph
of Fig. 8 shows the condition of Studio 1 at this stage? 'and Fig. 9(a)
the reverberation characteristic, taken in this condition.
It will be
seen that the floor is carpeted for approximately half its area and this
- 12is presumably responsible for the decrease in reverberation time above
700 c/s that has taken place since the last condition.
The peak at
1000 c/s is still prominent and would be expected to be noticeable if
present with the studio in use.
Final chords frO:11 a disk recordirig of the B.B.C. Welsh Orchestra
made on 1st May were therefore examined 9 using a high speed level
recorder and octave filters? and the reverberation time curve of
Fig. 9(b) was obtained~
It will be seen .that the peak at 1000 c/s
has almost disappeared.
CUI've 9{ c) for comparison i..; a plot o·f the
reverberation time calculated from the measured curve of the empty .
studio and taking into account the presence of a32~piece orchestra.
'J:1he values used for the ahsorptio'n"of(<?r~hestral players and theiJ.'
instruments were ~hose given by Bruel 1V).
The opportunity was taken during the final visit to hear the
Welsh Orchestra under Rae Jenkins playing both in Charles Street
Studio 9 Cardiff 9 and in Swansea No. 1.
Comparison recordings were
also made by Operations and Maintenance Department.
Compared with
Cardiff? the Swansea studio has a cleaner bass and the brass instruments do not tend to overpower the orchestra.
The conductor remarked
that it was now ppssible to allow the brass players their full
dy.lamic range.
'l'he instrumentalists themselves much preferred
. playing in the Swansea studio 9 being able to hear theElselves and
each other very much better.
The recordings gave the impression
of better perspective though less brilliance than Charles Street.
Tl10 studio will probably be too live for drama since there will
normally be fewer performers than in the orchestra, and also because
a studio requir,}s to be less reverberant for drama. than for music.
The sound insulation between the studio and its cubiole is·poor~ .
this will be improved by alterations to the cubicle windoV".
.
5~.
ACOU13'rrc IiIEASUREMENTS IN THE RJ@!'LAINIlifG SWANSEA STUDIOS
Both theso stUdios were found to require modification to make
them satisfac·t;ory and a report giving measurements on these studios
will be issued when they are in their final form.
rrhis is rJ. talks studio on the second floor using conventional
acoustic treatment.
It has satisfactory acoustics but the vonti-
- 13 lation noise might with advantage be reduced.
Fig. 10 shows the
reverberation curve, the main feature being a rise in the 300 - 400 c/s
region .which was not, however 1 very obvious on speeoh.
The cubicle
is somew~at over-reverberant in the bass.
CONCLUSIONS
The performance of Studio 1 has s:hown that Helmhol tzabsorbers may
be used as an alternative to membrane absorbers for bass absorption in
large studios.
It is unfortunate that absorption of sound over the
same fr~~uency band from other causes introduoed some uncertainties in
assessing the ampunt of absorption due to the resonators, but the latter
appears to have been close to the oalculated figure, -Some of the good
subjeotive features ,of the studio may be attributod to the diffusion
resul ting from the pro jection of the rectarlb"Ular units from the wall
surfaces.
When the Narrator's Studio and Studio No. 2 were cO:"lpleted they
were found to be not entirely satisfactory as regards acoustics and
sound insulation 9 and adjustments hav'B been made.
The acoustic faults
were partly due to the use of a glass wool absorber whioh has a lo~
density and a poor absorption coefficient a.t high frequenoies, and to
insufficient ceiling treatment.
The sound insulation problems were
not investigated but in the case of the three first floor studios, the
window construction was suspected.
(i)
Research Report B.041:
(ii)
C.L.S. GUford
"Helmholtz Resonators in the Acoustic Treatment
of Broadcasting Studios", British Journal of Applied Physics 9
Vol. 3 9 no. 3 9 March 1952
(Hi)
P.V. Brtiel "Panel Absorbonts ()f the Helmholtz :ryp'J", Symposium
of the Acoustics Group of the Physical Society, 1947, p.IO
(iv)
P.V. Brtiel
"Sound.. Insulation and Acoustics"
Chapman & Hall, 1951, p.132.
DIW
"Investigation of Helmholtz Resonators"
London,
- 14 APPENDIX
-~---
D.C. flow resistance measurements were made in the laboratory On a
series of fabrics~ with the object of finding a fabric with a resistance
similar to that of two layers of scrim.
No D.G, flow apparatus being
available a modified form of the techniQue described in Research Report
].041 was adopted 9 using a single Helmholtz resonator.
The materials
were placed across the neck of tue resonator and the change of Q factor
measured with a probe microphone.
Table (4) is a list of the values
obtained? al thoug':} high absolute accuracy is not claimed? it is believed
that the method gives reasonable comparison accuracy where tue fabrios
are tq be used under similar conditions to those of the test.
TABI:1!l...Lll
Material
R
f
--._._------_.---Cullums Scrim? one layer
11
11
two layers
Glares! No. 1
11
"11
"
11
"
"
"
0~16
0~24
" 2
"- 3
0:54
0:71
" 4
" 5
0~74
6
" 7
11
11
11
0~30
0~51
0:84
1.10
L18
1.47
8
9
------------------------------
----~
where Rf is the specific acoustic resistance in c.g.s. units.
(Dimensions
(M] (ir]-l [Lr2)
As a result of this measurement Glares' No. '3 cloth was used as a
repiacement for two layers of scrim used in the experiments of paragraph
3.2.
OJ
OJ
()
THIS PHOTOGRAPH IS THE PROPERTY OF
THE BRITISH BROADCASTING CORPORA
AND MAY NOT BE REPRODUCED OR
CLOSED TO A THIRD PARTY IN ANY f
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ABSORPTION OF PERFORATED PLASTERBOARD MOUNTED ON 3 INCH BATTENS.
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REVERBERATION CURVES OF SWANSEA STUDIO I
MEASURED AT FIVE STAGES IN CONSTRUCTION
27/12/52: BARE SHELL, ~OUGH PLASTERED
17/1 /52 : BARE SHELL. ROUGH PLASTERED WITH PLASTERBOARD PANEL UNITS ADDED
IB/I /52 : BARE SHELL , ROUGH PLASTERED WITH 110 c/s AND 200 c/s RESONATO~S ON STUDIO FLOOR
12/2/52 : ALL RESONATO~S INSTALLED AND TUNED
B /4/52 : APPROXIMATE LY HALF RESONATORS STOPPED. STUDIO COMPLETE EXCEPT FOR CARPET
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THIS PHOTOGRAPH IS THE PROPERTY OF REPORT No. B.05 2
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INSERTION OF TUHIHG TUBES AND HECK RESISTA NCES.
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SWANSEA No.1 STUDIO
DURING RECO NSTRUCTION.
(b) SHOW ING RESONATORS ON FLOOR.
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No. B.052
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PULSED . GLIDES OF SWANSEA STUDIO I
(a )
WITHOUT RESONATORS.
(b) WITH RESONATORS LAID ON FLOOR .
DECAYS IN (b)
NOTE
STEEPER AND MORE REGULAR
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ABSORPTION
DUE TO RESONATORS IN SWANSEA STUDIO I .
CALCULATED BY COMPARISON OF CURVES
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THIS PHOTOGRAPH IS THE PROPERTYt
REPORT 8.052
AP' O
THE BRITISH BROADCASTING CORPORAll
AND MAY NOT BE REPRODUCED OR
CLOSED TO A THIRD PARTY IN ANY FOR ~-------------WITHOUT THE WRITTEN PERMISSION OF
THE CORPORATION.
FIG.S
STUDIO No. I SWANSEA AFTER COMPLETION
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A pi D c::f.U,J.
REPORT No B052
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FIG.9
COMPARISON
OF REVERBERATION TIME CURVES TAKEN IN STUDIO I
WITH AND WITHOUT ORCHESTRA
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( b) WITH O RCHESTRA (ORCHESTRA CHORDS )
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REVERBERATION TIME CURVE OF STUDIO 3
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