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SPEAKER DIAMETER VS SPEAKER DIRECTIVITY

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An acoustical phenomenon not generally known or possibly overlooked is that a smaller diameter loudspeaker has a wider polar pattern than a larger diameter loudspeaker at a given frequency. In practical terms, a smaller diameter speaker can cover a given area in low level sound as well as if not better than a larger speaker provided certain other factors are present. We are, of course, assuming that the smaller speaker is satisfactory in reference to power handling capabilities and frequency response.

In order to pictorially demonstrate the above, the Atlas/Soundolier Engineering Department plotted the polar patterns of a 4" flat rigid piston and an 8" flat rigid piston at 1000, 3000, and 7000 Hz. The rigid piston was chosen in order to avoid the conclusion that the directivity patterns as shown were the products of a particular speaker or manufacturer.

The difference in the polar patterns for the 4" and 8" radiators at a particular frequency are quite striking. To illustrate the point, refer to figure 1. If we assume the sound pressure level on the axis is identical and at 60 db for both the 4" and 8" radiators and that the distance from the radiators remains constant for all measurements, at a point 30 degrees off the axis for 1000 Hz, the sound pressure levels are:

4" radiator - 58.2 db
8" radiator - 52.8 db

for 60 degrees off the axis

4" radiator - 55.2 db
8" radiator - 40.8 db

ATLAS / SOUNDOLIER ATAPCO SECURITY & COMMUNICATIONS GROUP

1859 INTERTECH DRIVE / FENTON, MISSOURI 63026 U.S.A. / TELEPHONE: (314) 349-3110 / FAX: (314) 349-1251

©1997 Atlas/Soundolier Printed in U.S.A. 00797 SL1-1190

Specifications are subject to change without notice