James E. Mitchell
Frazier Div., Sound-Craft Systems, Inc., Rt. 3, Box 319, Morrilton, AR 72110
The design of a proprietary loudspeaker for use in IMAX theaters posed some unusual problems while offering a unique opportunity: that of optimizing a loudspeaker design for a predetermined and relatively narrowly defined set of acoustic, geometric, and mechanical conditions. Requirements unique to the application, a specialty cinema format which employs six discrete audio signal channels and makes substantial demands on sound system bandwidth and acoustic output, are explained. Methods used to arrive at the final loudspeaker design are presented. Sound system coverage prediction software was utilized in a novel fashion, significantly reducing the time required to complete the development of the loudspeaker. Investigation of IMAX theater geometries indicated that a vertically asymmetric radiation pattern was highly desirable. Optimum loudspeaker directivity criteria were established, and horns were developed with these criteria in mind. Testing of prototypes indicated that the criteria had been substantially met. Predictive work was verified with in situ testing of prototype systems.