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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 , I N C .
sometimes also used to very good subjective effect, particularly in quite large rooms. Sound absorbent ma-
terials such as described above will alter the tonal characteristic of the room by making it sound “deader,”
less “bright and alive” and “quieter.” These changes also make the room more pleasant for conversation.
Diffusers, on the other hand, tend to not change the tonal balance characteristic of the room, but make the
sound smoother and more open.
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TANDING WAVES
Another type of reflection phenomenon is “standing waves.” Standing waves cause the unnatural
boosting or accentuation of certain frequencies, typically in the bass, to be found at certain discreet locations
on the room. A room generating severe standing waves will tend to make a loudspeaker sound one way
when placed in one location and entirely different when placed in another. The effects of standing waves on
a loudspeaker’s performance primarily as follows:
§ Tonal balance
§ Resolution of low-level detail
§ Sound-staging
Standing waves are more difficult to correct than slap echo because they tend to occur at a lower
frequency, whose wavelength is long enough to be ineffectively controlled by absorbent materials such as
Sonex. 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 posi-
tioning ASC tube traps in the corners of the room. Very serious low frequency accentuation usually requires
a custom-designed bass trap system.
Low frequency standing waves can be particularly troublesome in rooms constructed of concrete or
brick. These materials trap the bass in the room, unless it is allowed to leak out of the room, through win-
dows and doors.
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