Sound Physics Labs, Inc, the parent company of ServoDrive Inc., was awarded patent number 6,411,718 on June 25th, 2002 for its Unity Summation Aperture design; the driving force behind the company's well-received line of Boundary Compliant series including the SPL-trik and SPL-td1 loudspeakers.

The Unity Summation Aperture design is the creation of Sound Physics Labs' legendary sound engineer/designer Thomas Danley. The newly patented technology stems from a quest for (and realization of) true acoustic array ability and boundary compliance in loudspeaker performance.

SPL's Boundary Compliant loudspeaker designs are truly acoustically arrayable due to their highly directive characteristic. Features of the Unity Summation Aperture design include boundary compliance and the virtual elimination of lobing and comb filtering between adjacent SPL loudspeakers by focusing sound with directive precision. In addition, Unity Summation Aperture enables the entire loudspeaker to behave as a point source and keeps unwanted reflections to a strict minimum promoting boundary compliance. The new technology enables SPL loudspeakers to perform exceptionally well in reverberant and "difficult" acoustic environments.

The company's flagship loudspeaker, the SPL-td1, is a multiple entry horn utilizing Unity Summation Aperture to combine the outputs from multiple drivers to power a single horn. This allows each driver to operate in its own frequency range, driving a single one horn instead of usual multiple horns setup. The result is a multiple driver horn design that is automatically time/phase correct. This combined with the accuracy of projection provides an incredibly precise representation of sound across the frequency range, regardless of a listener's position.

Sound Physics Labs is the parent company of ServoDrive Inc., 1940 Lehigh Avenue, Glenview, IL 60025, Phone: (847) 724-5500, Fax: (847) 724-1953. Tom Danley, director of engineering, for both divisions designed groundbreaking servo motor driven subwoofers and the growing line of SPL loudspeakers. For more information, visit or