Audio Engineering

Acoustic Environment 95

Example
An anechoic room absorbs 99% of the energy received from the sound source. What
percentage of theLP from the source is refl ected? Assume 10 W of total energy output
from the source. Then the chamber absorbs 9.9 W of it.

Temperature

Reflective path

heater on

Space

heater





Reflective path

heater off

Figure 3.7 : Effect of thermal gradients in a room.

Box 3.1 Defi nitions in Acoustics

Sound Energy Density —is the sound per unit volume measured in joules per cubic

meter.

Sound Energy Flux— is the average rate of fl ow of sound energy through any specifi ed

area. The unit is joules per second (joules per second are called watts).

The Sound Intensity (or sound energy fl ux density)—in a specifi ed direction at a

point is the sound energy transmitted per second in the specifi ed direction

through unit area normal to this direction at the point. The unit is watts per square

meter.

Sound Pressure—is exerted by sound waves on any surface area. It is measured

in Newtons per square meter (now called pascals). The sound pressure is

proportional to the square root of the sound density.

(Continued)