Page 214 - Master Handbook of Acoustics

smaller rooms), all resonant modes are excited; this is because all modes terminate in the corners.

FIGURE 11-5 Equipment configuration for measuring the reverberation time of a room. (A)
Recording decays on location. (B) Later decay playback for analysis.

An omnidirectional microphone is positioned on a tripod, usually at ear height for a listening
room, or microphone height for a room used for recording. The smaller the microphone capsule,
generally the less its directional effects. Some larger-capsule microphones (e.g., 1-in-diameter

diaphragms) can be fitted with random incidence correctors, but using a smaller microphone (e.g.,
1/2-in-diameter diaphragm) is preferred for more uniform sensitivity to sound arriving from all
angles. In Fig. 11-5A, the microphone is a high-quality condenser microphone, part of the Brüel &
Kjaer (B&K) sound-level meter, but separated from it by an extension cable. This device provides a
preamplifier, octave filters, a calibrated method, and a line-level output signal for recording.

Measurement Procedure

The measurement procedure begins when wide-band pink noise is at a steady-state condition in the
room. The level is usually loud enough to require the use of ear protectors for everybody in the room.