Theatre Design & Technology - Feb 1970 - 28

The Influence of Theatre Chairs on Acoustics
DR. ING. WERNER GABLER
Berlin

(The following article appeared in the December
1967 issue of Buhnentechnische Rundschau
6/1967, pages 14·16. It was written as are·
joinder to an article published in Theatre Design
and Technology's May 1967 issue by ML B. W.
Hendrikson, American Seating Company, entitled
"Theatre Chair Acoustics" pp. 24·25. We repro'
duce DL Gabler's article here as a service to
TD&T readers, and as continuing evidence of
USITI's interest in dialogue among theatre prac·
titioners. EDITOR)

Some misconceptions prevail on the influence of theatre seats over audibility. This
misconception goes so far that on one occasion it was stated that the time-honored
acoustics of the Bayreuth Festival Hall are
so good only because it has unupholstered
chairs which are well known for their disdiscomfort. Next year, when the Festival
audience will be offered comfortable seating,
there need by no worry that the acoustical
environment will have been altered in any
way. The reason will be explained below.
An article by a member of the American
Seating Company (published in Theatre Design and Technology Number 9 (May 1967)
pp. 24-25) could be misunderstood. A
number of factors were mentioned which
could influence the degree of sound absorption in the significant frequency band from
125Hz to 4000Hz (cps). Unfortunately the
short article does not contain the essential
observation that the sound absorption of
the chairs is effective only as long as there
is no audience in the room. Minute differences in the manufacturi ng of the chairs,
and the kind of upholstery become unimportant as soon as the seat is filled with a
spectator.
In an audience seated in close rows, a
single seat occupies at least a space of
19-3/4" x 31-1 /2"; usuallythedimensions are a little more comfortable with
widths from 21-3 / 4" to 23-3/4" and
back-to-back distances from 33-1 / 2" to
35-1/2". Here, of course, the shape of
the chair plays a part. If armrests for greater comfort are introduced between seats,
the width, naturally, has to be increased.
If the chairs are tilted back very comfortably
and are equipped with deep upholstery, even
the unoccupied chair needs more depth
which then increases the necessary row
spacing. With very luxurious chairs therefore, it may be necessary to increase the
row spacing to more than 3 5-1 / 2".
However, the area occupi ed by the seated
audience always absorbs nearly 100% of
the arriving sound energy. Almost without
exception, the total absorption of the audience is large enough to make unnecessary
in theatres and concert halls the use of any

special acoustical tile or materials with
considerable absorption values. In older
theatres of the eighteenth and nineteenth
centuries, the room's reverberation time is
even sometimes shorter than desirable fer
music. In such theatres, the speech intelligibility is always good. (Keeping in mind
that a natural selection process weeded out
some less desirable European halls over a
275-year period. Editor) For music performance, especially for symphony concerts in
the old tiered-gallery theatres, a large part
of the stage house had to be used as a
kind of reverberation chamber. In this regard we should mention tests which were
undertaken in the Twenties on the State
Opera House, Berlin, to reinforce orchestra
sound electronically. At the time, the tests
produced unsatisfactory results, because the
state of th e technology was not yet sufficiently developed. During the reconstruction
of the building after the War, the consulting acoustician, Prof. Reichardt of Dresden,
tried every possibility conceivable to stretch
the reverberation time for even a few tenths
of a second beyond the original time. Newly
constructed theatres of the post-war period
usually have produced better acoustical conditions by means of larger volume in relation to the number of seats.
The acoustical characteristics of the chair
by itself, consequently, playa subordinate
role as long as the theatre of concert hall
is filled with audience members, because
in that case the sound absorption value of
the spectators themselves is decisive. However, in reality theatres and concert halls,
as far as time is concerned, are used more
frequently in their empty state for rehearsal.
For performers and musicians it is very disturbing to have to rehearse in a space
acoustically much different from the performance situation. This important condition
remains unmentioned in the American report mentioned above. The upholstery of the
seating in a theatre auditorium, therefore, is
not only an expenditure for the comfort of
the spectators, but it is one of the most
important acoustical variables, since the upholstered volumes compensate for part of
the absorptive capacity of the person. When
the surfaces of the seat and back cushions
are so dimensioned as to be covered later
by the person, the total amount of absorption in the filled auditorium will not be increased. This can be explained further by
the test data shown in Figures 1 to 3. Figure 1 is a reproduction of the graph in the
American report, which shows the amount of
the absorption dependent on the frequency.
This is particularly the case in curve" A"
with a thick cushion of good sound transmission in which the absorption increases
strongly towards the highs. Since extreme

absorption of the highs is desirable neither
for the intelligibility of speech nor for the
beauty of music, Hendrikson points out that
a flatter absorption curve can be achieved
by a denser stuffing of the cushion.

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Heavy Back Coating "B"

Figure 1: Unoccupied Chairs, after Hendrikson

Figure 2: Occupied Chairs
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Herkulessaal, Munich
After Bruckmeyer
After Kuhl
Hessischen Rundfunk, after Weisse

~ THEATER DESIGN AND TECHNOLOGY

FEBRUARY, 1970

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