### ASA 125th Meeting Ottawa 1993 May

## 4aAA6. A new in situ method to measure the directivity index.

**Gary W. Elko
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*Acoust. Res. Dept., AT&T Bell Labs., Murray Hill, NJ 07974
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The directivity index is a considerably useful measure in quantifying the
directional properties of electroacoustic transducers. For microphones used in
reverberant environments, the directivity index gives a rough estimate of the
gain in signal-to-noise ratio. The measurement of the directivity index of a
transducer is complicated by the need to measure over a spherical surface that
is in the far field of the transducer. This talk will present a new method for
measuring the directivity index in a diffuse reverberant environment. The
method uses the frequency response spectral variance to estimate the distance
from a point source to a point receiver in a reverberant field. If the
source-to-receiver distance, reverberation time, room surface area, and volume
are known, the directivity factor can be calculated explicitly from the spectra
variance. The method and its limitations will be discussed in the talk.