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Woof, Woof

-- by Marc Spiwak and John Woram

What exactly does a woofer do? For one thing, it takes advantage of an interesting phenomenon of human hearing. Due to the way the ear works, it's almost impossible to tell where a low-frequency sound originates. Then why are you so sure the string bass is over there on the extreme right? For one thing, you can see it. When you close your eyes, locating it becomes a bit more difficult.

The real audio cues that let you pinpoint the source of a low-frequency musical instrument are not the fundamental tones it produces. Instead, they're everything else-notably the higher-frequency overtones and especially the production noises, such as the little clicks and squeaks you might not even consciously perceive. They are nevertheless more than enough to inform the ear/brain combination of the sound's origin.

Part of the reason low-frequency sounds are difficult to pinpoint is their long wavelength. A sound wave's length is inversely proportional to its frequency. So the lower (smaller) the frequency, the longer (larger) its wavelength. As a result, the amplitude of a low-frequency sound at each ear is practically identical, regardless of where it originates. By contrast, there may be considerable variations as a high-frequency (short wavelength) sound reaches the ears.

Put it all together and you find the ears depend on higher frequencies to determine a sound's location. Take it all apart and you have the modern speaker system, with two tiny speaker cabinets on the desktop and a larger enclosure that sits on the floor somewhere out of sight. A filtering system sends the high-frequency signals to the appropriate left or right speaker, which doesn't have to be very large to handle them. The lower frequencies go to the satellite woofer. Because they contain no useful directional information, two such woofers are unnecessary.

In a reasonably good environment, you shouldn't even be aware of the woofer's presence. Less-knowledgeable friends may be amazed at the bass response of your dinky little speakers.

Copyright (c) 1997 CMP Media Inc.

Windows Magazine, March 1997, page 216.

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