Handbook for Sound Engineers

Acoustics for Auditoriums and Concert Halls 171

produces balance problems with musical performances,
leaving questions regarding the arrangement of the
orchestra instrument groups unsolved. Elliptical ground
plans, Fig. 7-26F, are, without reflection-supporting
measures, acoustically suited only for locally fixed
sound sources. This general utilization is not recom-
mended owing to the focus formation in the perfor-
mance zone as well as in the audience area. This refers
especially to the atrium courtyards of unstructured glass
walls and plane floor in large office buildings, which are
a modern architectural trend. These functionally
designed entrance foyers are often used for large
musical events which, however, can in no way satisfy
any room-acoustical requirements.

7.3.3.2.2 Ceiling

In general, the ceiling configuration contributes little to
spaciousness of the sound field, but all the more to
achieving intelligibility with speech, clarity with music,
volume, and guidance of reverberation-determining
room reflections. For speech, the reverberation time

should be dimensioned as short as possible. Therefore

the ceiling should be configured in such a way that

possibly each first sound reflection reaches the middle

and rear audience areas, Fig. 7-28. For musical perfor-

mances the mean ceiling height has to comply with the

volume-index requirements. For achieving an as long as

possible reverberation time, the ceiling should have its

maximum height where the length or width of the room

is maximal. The repeated reflection of the sound energy

by the involved boundary surfaces produces long travel

times, while the required slightness of energy reduction

by the reflections has to be insured by a negligible

sound absorption coefficient of these surfaces.^35 Thanks

Figure 7-26. Examples of so-called arrangement patterns
(confrontations) between performers and listeners in a
room with curved boundary surfaces.

A. B.

C. D.

E. F.

Figure 7-27. Propagation of the wave front in a circle

(caustic).

Figure 7-28. Examples of acoustically favorable ceiling

designs.

Section

Ground plan