Point Source Loudspeaker Design: Advances on the Inverse Horn Approach

The conventional design of an omnidirectional source uses a polyhedral speaker to emulate a spherical radiating sound wave. But this approach does not work at short distances and at higher frequencies. The inverse horn design proposed by Polack, a conventional loudspeaker matched to a small aperture through a reverse horn, provides a good approximation to an omnidirectional point source. But this solution has a rather irregular frequency response that arises from the acoustic resonances of the air inside the horn cavity. This research described two implementations of an equalized reverse horn source that have the desired directional characteristics of a point source with a flat frequency response of +/-3 dB from 100 Hz to 8 kHz. There are various trade-offs in selecting the sizes.