Speakers of the House

How do you build a speaker equipped with both better sound and adjustable sound?

By David J FishmanApr 1, 1992 6:00 AM


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Since the introduction of the hi-fi speaker, audio engineers have been trying to perfect the reproduction of musical sound. Each year consumer-electronics companies introduce yet another generation of speakers that boast more accurate performance, wider dynamic range, or improved frequency response.

But when audiophiles set up the speakers at home, they’re often disappointed. As they quickly discover, the sofas, drapes, carpeting, and furniture that fill the average room give it a unique acoustical profile that can distort sound from even the best speakers. The problem, says Laurie Fincham, technical director at Britain’s KEF Electronics, is that most of us don’t decorate our living rooms like an audio engineer’s acoustic laboratory or an electronics store’s carefully designed sound room.

The answer is to build a speaker equipped with not just better sound but adjustable sound--sound that can be modified to accommodate the surroundings. For years work on such a smart speaker languished, principally because perfecting the new technology required an enormous amount of research into how sound behaves in practical settings--an undertaking too expensive for any single electronics company.

That sound barrier may soon be broken. Five years ago, as part of the Eureka program designed to foster technological competitiveness, 19 European nations inaugurated the Archimedes project, an audio research effort coordinated through KEF, Bang & Olufsen of Denmark, and the Acoustics Laboratory of the Danish Technical University. Archimedes is now well on its way to making the smart speaker a reality.

The researchers decided early that it would be impractical to do acoustical tests in a variety of real rooms because moving the sensitive monitoring equipment would be too cumbersome and expensive. Instead they developed a way to simulate the sound properties of any space. Inside a noiseless, anechoic chamber at the Technical University of Denmark they created the first virtual-reality sound room.

The experimental room includes 32 speakers carefully arranged in a six-meter sphere around a raised listening chair. Although all the speakers are designed to play the same sound track, a central computer can delay or attenuate the production of sound in any or all of them by as little as a millisecond, just as if the sound were reflected or absorbed by the surfaces of an actual room. By attenuating high-frequency sounds in one or more of the speakers, for example, the computer can simulate the absorption of sound waves by furniture, drapes, or carpet. By delaying the sound just a bit, it can simulate what happens when you move a speaker farther from the reflective surface of a wall. The listener is surrounded by a gauzy curtain that conceals the speakers but is transparent to sound. This eliminates any visual cues that might reveal the actual source of each sound.

When you are sitting in the chair, Fincham says, it’s impossible for you to tell you’re some twenty feet off the ground in this huge test chamber. You feel like you’re in someone’s living room.

In this room the researchers hope to reveal how a listener’s perception of sound changes in different kinds of environments. They will then use the room to build and test the new generation of speakers, able to adapt to these environments.

So far they haven’t settled on a final smart speaker design. But one likely system would use sonar signals to take a reading of a room’s acoustical signature and determine which portions of the sound spectrum it affects the most. The speaker would then be instructed to adjust its output in those tonal ranges to compensate for the distortion. A cheaper system might involve a retailer’s visiting a consumer’s house and taking an acoustical reading of the intended listening space. The speakers could then be permanently programmed at the store to best accommodate that room. Either way, Fincham expects that the project will have far more benefit to the average listener than any of the laboratory only improvements developed in the last decade.

Whatever the final outcome of Archimedes, he says, we’ve at least begun the process of getting our priorities straight.

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