Handbook for Sound Engineers

216 Chapter 9

ular after WWII and are still used today by some
designers when access to other modeling tools is limited
and/or when a physical representation of the space
under review is needed for the purpose of testing as well
as visualization.

The scaled approach used in the geometrical
construction of the model implies that in order to inves-
tigate some of the relevant physical parameters,^1
specific acoustic variables will also need to be scaled
accordingly.

9.2.1.1 Frequency and Wavelength Considerations in

Physical Models

The issues pertaining to frequency and wavelength in

scale models are best presented with the use of an

example. If a source of sound generating a frequency

f= 1000 Hz is placed inside a room, then under standard

conditions of temperature (t= 20°C) where the velocity

of sound is found to be c = 344 m/s, the wavelength of

the sound wave is obtained from

(9-1)

or in this example

The wave number k can also be used to represent the

wavelength since

(9-2)

so in our example we have

Figure 9-2. External view of a 1:20 scale physical model.
Courtesy Kirkegaard Associates.

O c

f

=--

l=0.34 m

k^2 S

O

=------

k=18.3 m1–

Figure 9-3. Internal view of a 1:20 scale physical model. Courtesy Kirkegaard Associates.