REVIEWS OF ACOUSTICAL PATENTS

• GEORGE L. AUGSPURGER, Perception, Incorporated, Box 39536 Los Angeles, California 90039

George E. Short, III et al., assignors to WISDOM AUDIO CORP.

9 April 2024; filed 19 May 2022

One type of planar diaphragm loudspeaker has a single-layer meandering voice coil attached directly to a thin plastic diaphragm. The voice coil is immersed in a lateral magnetic field generated by small magnets above and below the diaphragm. Sound emerges from gaps between the magnets. Voice coil heating can be a problem, even at moderate power levels, since it alters the tension and internal damping of the plastic diaphragm. This patent describes a vertical array of such devices in which rear thermal plates have been added to improve heat dissipation. —GLA

Lars Risbo et al., assignors to PURIFI APS

9 April 2024; filed 12 February 2020

A long-throw low frequency loudspeaker usually employs a long voice coil that overhangs a relatively short magnetic gap. In many designs, the diameter of the voice coil gap is not much larger than the center pole piece. As a result, the fringe magnetic field below the gap is stronger and deeper than the fringe field above the gap, and the asymmetrical fields create an asymmetrical driving force. This patent explains how distortion can be reduced by adding a magnetic structure above the pole piece, as shown. —GLA

Eric Freeman and David Dick, assignors to BOSE CORPORATION

9 April 2024; filed 7 August 2021

Numerous Dolby patents describe methods for reproducing immersive audio from a loudspeaker setup that is less than optimum. Corrective signal processing is applied to individual loudspeakers according to their placement in relation to a specified listening location. This Bose patent carries the process two steps further. Sensors detect the location of an actual listener, and signal processing includes compensation for loudspeaker directionality, even if the listener is behind one or more loudspeakers. —GLA

Franck Giron and Michael Enenkl, assignors to SONY GROUP CORPORATION

23 April 2024; filed 25 March 2020

Almost all surround sound installations in automobiles and home listening rooms employ bass management to reduce the size and cost of individual loudspeakers. Low frequency information from all channels is combined and reproduced by a single subwoofer. This simplification does not degrade the localization of individual sound sources, but, as this patent points out, it may well affect the timbral balance of individual channels. Moreover, the relative locations of individual loudspeakers may introduce unwanted coloration. This patent sets forth a method for creating corrective signal processing based on the “spread factor” of individual loudspeakers. The Detailed Description is very long, uses a lot of big words, and includes math formulas, but fails to supply much help in understanding how a practical implementation might be developed. —GLA

Sean O'Brien and Stuart W. Lumsden, assignors to Polk Audio, LLC

30 April 2024; filed 29 July 2020

The cone of a wide-range loudspeaker must operate well above the range of piston-like motion, and special features may be employed to counteract the effects of cone breakup. For example, corrugations, damping patches, or stiffening ribs may be added. This patent describes a special cone contour that includes molded dimples to control breakup modes. —GLA

Timothy Degraye et al., assignors to HED Technologies SARL

30 April 2024; filed 24 August 2020

High-quality headphones can provide extended low frequency response at very high levels, but they cannot duplicate the tactile sensations generated by a powerful subwoofer. This patent suggests that the deficiency can be overcome by simply adding a powerful subwoofer. —GLA