The principle of Bending Wave Speakers
One of the ways to illustrate the basic principle of how bending wave speakers operate, the following image could be helpful. By throwing a stone into the lake, the water surface is being destabilized by its impulse. This shows that the wave created from this action propagates equally on each side. This principle also stands when it comes to bending wave loudspeakers. An electrodynamic motor raises the wavefront on the membrane. This wavefront propagates on the membrane, exactly like the wavefront on the water surface. A bending wave has emerged. Due to the change of the air pressure resulting from this wavefront we hear the acoustic tone.
Bending wave transducers, or loudspeakers, use a diaphragm that is intentionally flexible. The rigidity of the building material increases from the center to the outside. Short wavelengths radiate primarily from the inner area, while longer waves reach the edge of the speaker. To prevent reflections from the outside back into the center, a surrounding damper absorbs the long waves. Such transducers can cover a wide frequency range (80 Hz to 35,000 Hz) so they are close to an ideal point sound source. Only a very few manufacturers take this uncommon approach, in very different arrangements.
The History of Bending Wave Speakers
The Ohm Walsh loudspeakers use a unique driver designed by Lincoln Walsh, who had been a radar development engineer in WWII. He became interested in audio equipment design and his last project was a unique, one-way speaker using a single driver. The cone faced down into a sealed, airtight enclosure. Rather than move back-and-forth as conventional speakers do, the cone rippled and created sound in a manner known in RF electronics as a “transmission line”. The new speaker created a cylindrical sound field. Lincoln Walsh died before the release of his speaker to the public. The Ohm Acoustics firm has produced several loudspeaker models using the Walsh driver design since then. German Physiks, an audio equipment firm in Germany, also produces speakers using this approach.
The German firm, Manger, has designed and produced a bending wave driver that at first glance appears conventional. In fact, the round panel attached to the voice coil bends in a carefully controlled way to produce full-range sound. Josef W. Manger was awarded the “Diesel Medal” for extraordinary developments and inventions by the German institute of inventions