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Method and Circuit for Improving the Polar Response of a Two-Way Horn-Loaded Loudspeaker System

US Patent: 5,784,474
Date Filed: November 10, 1994
Date Issued: July 21, 1998
Inventors: Paul Kohut, Peter C. Soper, John D. Meyer
A true point source exhibits a single acoustical center from which all frequencies radiate uniformly with coherent phase response. To the listener, sound emanating from an ideal point source is precisely defined in space and exhibits characteristics subjectively described as "natural."

Although an ideal full-range loudspeaker could theoretically function as a perfect point source, no device yet invented can maintain anything close to constant amplitude response across the full audio spectrum. Conventional two-way systems do a much better job of producing flat response from 20Hz to 20kHz, but, in doing so, they sacrifice the common acoustical center. Inevitably, phase and amplitude anomalies are introduced by the crossover filters and vastly different physical characteristics of the low- and high-frequency drivers. Matters are complicated further when horns are introduced into the equation, since the acoustical center of a horn is usually frequency dependent. Consequently, conventional two-way horn-loaded loudspeakers will have a shifting, poorly defined acoustical center. This, in turn, produces inconsistent mid- and high-frequency beamwidth as well as troublesome lobing effects, both of which degrade overall sound system performance when multiple cabinets are combined in arrays.

This patent introduces techniques for designing loudspeaker systems that produce maximally flat amplitude and phase response throughout a defined "listening window," essentially creating a near-ideal point source within the specified dispersion pattern. To achieve this goal, the Meyer Sound engineering team developed tunable phase and amplitude correction circuits for insertion before the crossover, as well as a phase-shifting network inserted between the crossover and the power amplifier driving the woofer.

The technology behind this patent has been successfully implemented in Meyer Sound's self-powered UPA-1P and -2P loudspeaker systems, as well as other products. Meyer Sound engineers realized that both electrical and acoustical variables must be considered as an integrated whole to achieve their elusive goal of establishing a common and stable acoustical center, and it should be noted that significant advancements in high-frequency horn design also contribute to the exceptionally uniform and predictable dispersion characteristics of the UPA-1P and -2P. However, due to the peculiar nature of the patent process, the electronic circuits and horn designs were split into separate patent applications.

Also, as a practical matter, application of this technology is limited to self-powered systems since the precise amplitude and phase response of the amplifiers must be taken into account. Although the patented circuits could produce the same results in systems with external power amplifiers, exhaustive recalibration would be required for each new amplifier type used.