WILSON AUDIO Watch Dog, Owner'S Manual

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W i l s o n A u d i o S p e c i a l t i e s
Standing waves are more difficult to correct than slap echo because they tend to
occur at a lower frequency. Absorbent materials, such as Illbruck Sonex®, are ineffec-
tive at controlling reflections in the bass region. Moving speakers about slightly in the
room is, for most people, their only control over standing waves. Sometimes a change
of placement of as little as two or three inches can dramatically alter the tonal balance
of a small system.
Fortunately, minor low frequency standing waves are well controlled by position-
ing ASC Tube Traps™ in the corners of the room. Very serious low frequency accentua-
tion usually requires a custom-designed bass trap system.
Low frequency standing waves can be particularly troublesome in rooms con-
structed of concrete or brick. These materials trap the bass in the room unless it is al-
lowed to leak out of the room through windows and doors.
In general, placement of the speaker in a corner will excite the maximal number
of standing waves in a room and is to be avoided for most direct radiator, full-range
loudspeaker systems. Some benefit is achieved by placing the stereo pair of loudspeak-
ers slightly asymmetrically in the listening room. This is so the standing waves caused
by the distance between one speaker and its adjacent walls and floors are not the same
as the standing wave frequencies excited by the dimensions in the other channel.
Comb Filter Effect
The “comb filter” effect is a special type of standing wave noticeable primarily at
higher frequencies and shorter wavelengths.
Acoustical comb filtering occurs when sound from a single source, such as a loud-
speaker, is directed toward a microphone or listener from a distance. The first sound
to reach the microphone is the direct sound, followed by a delayed, reflected sound.
At certain frequencies, cancellation occurs because the reflected sound lags in phase
relative to the direct sound. This cancellation is most apparent where the two frequen-