Handbook for Sound Engineers

Acoustics for Auditoriums and Concert Halls 173

of curvature should therefore be above half the total
height of the room or below twice the height, Fig. 7-31.

(7-48)

According to Cremer^9 it is guaranteed in this case

that there do not originate from the curved ceiling any

stronger reflections towards the receiving area than

from a plain ceiling at apex height.

7.3.3.2.3 Balconies, Galleries, Circles

With proper arrangement and dimensioning, balconies

and circles may have an acoustically favorable effect,

since they contribute to a broadband diffuse sound

dispersion and are also able to supply initial reflections

for enhancing clarity and spatial impression. In this

respect it is necessary, however, to decide if these

reflections are desirable. Fig. 7-32A shows a graph of

long-delayed sound reflections which give rise to very

disturbing echo phenomena, the so-called theater

echoes. Instrumental in the generation of these reflec-

tions is, first of all, the rear wall in combination with

horizontal architectural elements (circle, gallery,

balcony, ceiling). The disturbing effect of these sound

reflections has to be avoided. Protruding balconies are,

thanks to their horizontal depth, capable of shading

these corner reflectors and to turn the reflections into

useful sound, Fig. 7-32B.

The arrangement of far protruding circles is acousti-

cally problematical with regard to the depth D (distance

of the balustrade or of a room corner above it from the

rear wall) and the clearance height H of the circle above

the parquet or between two circles arranged one above

the other. If the protrusion is very deep, the room area

situated below it is shaded against reverberant sound

and clarity-enhancing ceiling reflections. This area may

be cut off from the main room and have an acoustic

pattern of its own with strongly reduced loudness,

unless certain construction parameters are observed,

Fig. 7-33.2,7,9

7.3.3.3 Room Topography

7.3.3.3.1 Sloping of Tiers, Sight Lines

For all room-acoustical parameters describing time and

registers clarity, the energy proportion of direct sound

and initial reflections is of great importance. With the

sound propagating in a grazing fashion over a plain

audience area there occurs a strong, frequency-depen-

dent attenuation (see Section 7.3.4.4.4). Also, visually,

such a situation implies considerable disadvantages by

obstruction of the view towards the performance area.

These disturbing effects are avoided by a sufficient and,

if possible, constant superelevation of the visual line.

Figure 7-30. Ceiling configurations for obtaining
energy-rich initial reflections in the middle and rear listener
areas.

Figure 7-31. Focusing due to vaulted ceilings.

r h

2

--- or rtd 2 h

A.

B.

C.

D.

r

h

r

h