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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 .
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 loudspeakers slightly asymmetrically in the listening room. This is so
that the standing waves caused by the distance between one speaker, its adjacent walls and floors are not the
same as the standing wave frequencies excited by the dimensions in the other channel.
C
OMB 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 loudspeaker, is di-
rected 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 are 180 degrees out of phase. Further, there is augmentation at other frequencies where the direct and
the reflected sounds arrive in phase. Because it is a function of wavelength, the comb filter effect will notch
out portions of the audio spectrum at regular octave-spaced intervals. The subjective effect of comb filter
effects is as follows:
§ Added roughness to the sound
§ Reduction of harmonic richness
§ Smearing of lateral sound stage image focus and placement
Comb filter effects are caused by side wall reflections. These are best controlled by careful speaker
placement and by the placement of Sonex or air duct panels to the part of the wall where the reflection oc-
curs.
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