Edition: U.S. / Global

SOUND; Pioneering Audio Design To a Consistently Musical Beat

By Hans Fantel
Published: July 29, 1990

Despite its present multi-billion-dollar size, the audio industry started small - in the traditional American fashion of free enterprise and better mousetraps.

The birth of audio - as distinct from mass-market radios and phonographs - may be dated roughly to 1937. That year a book designer named Avery Fisher, with the aid of some self-taught electronics, built what was probably the world's first high-fidelity phonograph in a Manhattan loft. After the war, he became a leading manufacturer of sound equipment. Still very much alive, Mr. Fisher has seen his name perpetuated through the great concert hall he endowed at Lincoln Center as the home of the New York Philharmonic.

Not all audio pioneers have been so fortunate. Some of the greatest have fallen into oblivion. Such is the case with Stewart Hegeman, who, in the 1940's and 50's, formulated several basic concepts for modern amplifiers and invented omnidirectional loudspeakers. Many of his ideas, once spurned, are now universally accepted. Yet even in the technical literature, Mr. Hegeman is rarely given credit for his contributions.

''I always wanted to be a concert violinist,'' Mr. Hegeman told an interviewer not long before his death in 1986. ''But I was never any good on the fiddle. For me, engineering turned out to be the easiest way to get close to music.''

This remark points to his method. Stewart Hegeman always put musical judgment ahead of established engineering practice - an approach that at the time struck most professional engineers as exotic, to put it mildly. Despite his impeccable credentials, he could muster little sympathy for a music-oriented approach in an industry that still regarded sound equipment as plain electronic hardwaree. Working alone, he was a holdover from the days when individual inventors - relying on little more than creative imagination - laid the technical groundwork for entire industries.

While serving as a consultant to Harman-Kardon, a pioneering audio company, Hegeman developed a theory of amplifier design based on ultra-wide frequency response. He argued that the frequency response of an amplifier should not be limited to the range of human hearing (20 to 20,000 Hertz) but should extend far above and below it.

This notion was promptly shrugged off. Why bother with frequencies you can't hear?

Hegeman countered that the narrow response limits of amplifiers at that time actually reflected distorting waves back into the audible range - somewhat as a sea wall throws back the surf. But at the time there was no way to confirm this through measurement. The argument could only be stated in complex mathematical terms understood by few practical engineers. Besides, few were musically astute enough to appreciate the difference in sound (as demonstrated in several amplifiers built by Harman-Kardon on the Hegeman principle), and so the issue was largely ignored.

It took nearly two decades for Hegeman's wide-band principle to be recognized as essential for low-distortion amplifiers. Today, nearly all makers of high-quality audio amplifiers adhere to it, at least to some degree. Harman-Kardon, the company for which the original research was done, has refined this principle in the current models of its exemplary Citation Series.

Hegeman was also far ahead of his time in recognizing that negative feedback - a widely used method of reducing measurable distortion - was itself the source of different kinds of distortion that went undetected in the laboratory but gave the sound a strange touch of brittleness. Again, Hegeman could confirm his hunch only with his ears and his slide rule, still lacking appropriate tools to obtain supportive laboratory data.

Much later, as suitable measurement methods became available, controlled experiments at the State Technical Research Center in Oulu, Finland, and at the University of Osaka, Japan, bore out Hegeman's findings. As a result, nearly all the best amplifiers today employ little or no feedback, resulting in greater clarity and a generally sweeter, smoother sound.

Aside from laying the foundation for much of modern amplifier design, Hegeman also built the first multidirectional home loudspeakers. His idea of creating a more natural acoustic ambiance by scattering the sound in many directions has not been widely adopted. Still, at least two major speaker manufacturers - Bose and Ohm - have popularized this approach, and a small company, Morrison Loudspeakers of Toronto still produces Hegeman's original loudspeaker designs.

Stewart Hegeman's work was not confined to audio. Back in the 1950's, he built what may well have been the first large-screen projection television set for a bar in his New Jersey neighborhood. And as early as 1964 - 12 years ahead of Sony's Betamax - Hegeman had a working model of a home video tape recorder in his basement lab in Glen Ridge, N.J.

Lacking the money to develop and market this product, he tried to interest several electronics manufacturers in the idea of home video recording. There were no takers.