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Subwoofer Placement
Subwoofers offer somewhat greater flexibility in placement since the frequencies they
reproduce are not readily localizable by the human ear. This is because the wavelengths
they reproduce are more than ten feet (3 meters) long, but our ears are located only
about 6-7 inches (17 cm) apart. Thus, these extremely long waves do not contribute
meaningfully to the imaging that the main speakers create.
However, this fact does not mean that the placement of the subwoofers has no effect
on the sound quality in the room. Far from it. The subwoofers are the
most likely to
suffer from the response irregularities introduced by the room itself, operating as they
do below approximately 80 Hz in most systems.
Recent research into the behavior of rooms as a function of speaker placement has
concluded that – if you have the freedom to do so – there are significant advantages to
placing several smaller subwoofers around the room, rather than relying on a single
large woofer. Moreover, the optimum placement is usually centered on each of the four
walls, or deep in the corners of the room. If you have the luxury of doing so, this simple
placement strategy can reduce the size of the room’s response irregularities from 20
decibels down to perhaps as little as 6-8 decibels – a tremendous improvement.
Reducing the room’s inherent problems to this degree provides a huge advantage.
Room Treatment
Rectangular rooms have six reflecting surfaces (four walls, ceiling, and floor)
that reflect sound to the listener, after various delays introduced by the indirect routes
the sound take on their way to the listener. These first reflections are particularly
damaging to sound quality. Looking at the simplest case of stereo reproduction, you
have a minimum of
twelve first reflection points in your room that deserve some
attention.
Unfortunately, it is often difficult to do much about the ceiling and floor reflections,
even though they are arguably the most destructive. (The minimization of these
reflections is one of the strongest arguments for the tall, line source loud- speakers that
Wisdom Audio builds.) This leaves you with eight “first reflections” that you should
consider minimizing somehow. These points are easily found by having an assistant slide
a small mirror along the four walls of the room, while you sit at the listening position.