Matsushita's "Sound Window"

As normally conceived, loudspeakers use electrodynamic forces to control the movements of their diaphragms, which in turn move air. Matsushita Electric Industrial Co., Ltd. has come up with an interesting twist on this principle, one in which air pressure itself ("aerodynamic-drive technology") is used to control the diaphragm. The result is a transparent panel speaker called the "Sound Window," announced by the Japanese industrial giant March 27.

The invention is intended to mate acoustic radiating surfaces with video displays, enabling the launch of sound and image from the same surface—or at least, from two closely-spaced surfaces—thereby eliminating the need for the deep cavities required to house traditional moving-coil drivers. The goal is maximum performance with minimal energy expenditure from an integrated audio/video source with shallow depth—in other words, a television-like device that can be hung on the wall like a framed picture.

Sound Windows employ a lightweight transparent panel suspended a fraction of an inch from another surface, such as a video screen. The sound pressure from a small conventional cone driver acoustically vibrates the transparent panel, which can be 10 times—or more—greater in diaphragm area. The aerodynamic-drive technology is said to ensure sound-pressure transmission to the entire panel surface. Matsushita claims this "acoustic leverage technology" enables the Sound Window to operate on as little as 1/25 the power a conventional driver would require. Panel shape isn't critical, the manufacturer states.

With varying degrees of success, other manufacturers have experimented with flat-panel speakers. Matsushita claims that the Sound Window is the industry's first speaker "that reproduces sound by pneumatically vibrating a transparent panel using aerodynamic-drive technology." The device appears to offer the most promise for use in small communications products, such as cell phones, personal digital assistants, and laptop computers. The Sound Window's extremely low power consumption would appear to make it ideal for such applications. Matshushita plans to ship the first Sound Window products to industrial customers later this year.

Matsushita doesn't specify the frequency response, distortion level, or output capability of the Sound Window. Presumably, none of these specifications is audiophile grade, but the ingenious device proves that new designs for sound generation are possible for inventors who think outside the box. A complete press release, including an operation diagram, can be seen here.