Handbook for Sound Engineers

1344 Chapter 35

35.1.3.2 Loudspeaker Types

We distinguish the following loudspeaker types:

• Point sources.


• Loudspeaker columns.

•Cluster.

• Line arrays.


• Digitally controlled sound columns.

For the use of these different sound radiators, their
performance parameters must be known. One will soon
note, however, that the performance parameters speci-
fied by the manufacturers vary in accuracy and scope.
For nearly two decades the Standards Committee of the
AES has been trying to update rules and standards for a
uniform approach in this respect.^7 When studying the
data sheets of diverse manufacturers one will neverthe-
less note considerable discrepancies allowing the expert
to draw conclusions as to the quality of the data given.
For this reason we are going to mention the most impor-
tant data to be specified in loudspeaker design. Let us
start with the so-called point sources.

35.1.3.2.1 Point Sources

Point sources do not show automatically omnidirec-
tional radiation behavior. Their directivity behavior is
measured on a turntable and all directivity balloon data

is referred to the point of rotation, therefore the name

point sources.

Transfer Behavior. The nominal load capacity Pn of

this loudspeaker type is the rms electrical power speci-

fied by the manufacturer according to the design

characteristics.

The ratio between the sound pressure and the

voltage required to attain this capacity at the radiator

is called sensitivity Ts.

(35-3)

One distinguishes between a free-field sensitivity Td

and a diffuse-field sensitivity Tr. The free-field sensi-

tivity is normally indicated for a reference point on the

reference axis at a distance of 1 m from the loudspeaker.

This can be expressed by

(35-4)

The diffuse-field sensitivity has to be ascertained in

a diffuse field, for instance in a reverberant chamber. In

order to eliminate the room property characterized by

the equivalent absorption area of the room, a correction

factor has to be used:

Figure 35-6. Level and frequency range of natural sources and instruments. Courtesy V. O. Knudsen 1932.^5

p ̃

u ̃

Ts p

̃

u ̃

---=

Td

p ̃d r

u ̃r 0

=---------