Handbook for Sound Engineers

162 Chapter 7

tion time coincides with the objectively measured rever-
beration time.

7.2.2.15 Register Balance Measure (BR) (Tennhardt)

With musical performances, the relation of the partial
volumes of individual orchestra instrument groups
between each other and to the singer is an important
quality criterion for the balance (register balance) and is
defined by the frequency-dependent time structure of
the sound field.^28 The register balance measure BR
between two orchestra instrument groups x and y is
calculated from the A-frequency weighted volume-
equivalent sound energy components of these two
groups, corrected by the reference balance measure Bxy
of optimum balance.

(7-45)

where,
Bxy is in dBA.

Group A: String instruments,
Group B: Woodwind instruments,
Group C: Brass instruments,

Group D: Bass instruments,

Group S: Singers.

Significant differences in balance do not occur if

4dBA<BR<4 dBA and if this tendency occurs

binaurally.

7.3 Planning Fundamentals

7.3.1 Introduction

When planning acoustical projects one has to start out

from the fundamental utilization concept envisaged for

the rooms. In this respect one distinguishes between

rooms intended merely for speech presentation, rooms

to be used exclusively for music performances, and a

wide range of multipurpose rooms.

In the following we are going to point out the most

important design criteria with the most important

parameters placed in front. Whenever necessary the

special features of the different utilization profiles will

be particularly referred to.

Strictly speaking, acoustical planning is required for

all rooms as well as for open-air facilities, only the

scope and the nature of the measures to be taken vary

from case to case. The primordial task of the acoustician

should, therefore, consist in discussing the utilization

profile of the room with the building owner and the

architect, but not without taking into consideration that

this profile may change in the course of utilization, so

that an experienced acoustician should by no means fail

to pay due attention to the modern trends as well as to

the utilization purposes which may arise from or have

already arisen from within the environs of the new

building or the facility to be refurbished, respectively.

On the one hand it is certainly not sensible for a

small town to try to style the acoustical quality of a hall

to that of a pure concert hall, if this type of event will

perhaps take place no more than ten times a year in the

hall to be built. In this case a multipurpose hall whose

acoustical properties enable symphonic concerts to be

performed in high quality is certainly a reasonable solu-

tion, all the more if measures of variable acoustics and

of the so-called electronic architecture are included in

the project.

In rooms lacking any acoustical conditioning what-

soever, on the other hand, many types of events can be

performed only with certain reservations, which have to

be declined from the acoustical point of view.

Table 7-5 shows the interrelation between utilization

profile and effort in acoustical measures. These

Figure 7-18. Subjectively perceived reverberation time
RTsubj as a function of reverberance measure H and objec-
tive reverberation time RT 60 as a parameter.

Group x

AB CDS

A 5.8 1.5 (^0) 2.8
Group y B5.8 7.3 5.8 3.0
C 1.5 7.3 1.5 4.3
D05.8 1.5 2.8
S2.83.0 4.3 2.8 
BRxy 10
Efx
Efy

©¹
log§·dB A B
= + xy