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Structural Resonance
Structural resonances are familiar to most people as buzzes and rat tles, but this type
of resonance usually only occurs at extremely high volume levels and is usually masked by
the music. In many wood frame rooms the most common type of structural resonance prob-
lem is "booming" of walls and floors. You can test for these very easily by tapping the wall
with the palm of your hand or stomping on the floor. Most rooms exhibit mid-bass "boom"
when struck. The loudspeaker playing in the room also excites these resonances. To give
you an idea of what the perfect wall would sound like, imagine rapping your hand against
the side of a mountain. Structural wall resonances generally occur in the low to mid-bass
frequencies and add a false fullness to the tonal balance. They, too, are more prominent
at louder levels, but their contribution to the sound of the speaker is more progressive.
Rattling windows, picture frames, lamp shades, etc., can generally be silenced with small
pieces of caulk or with blocks of felt. However, short of actually adding additional layers
of sheet rock to flimsy walls, there is little that can be done to eliminate wall resonances.
Volume Resonance
The physical dimensions and volume of air in a room will also support standing wave
modes and resonances at frequencies determined by the size of that room. Larger rooms
will resonate at a lower frequency and have more complex (bet ter) modal distributions
than will smaller rooms. Volume resonances, wall panel resonances, and low frequency
standing waves combine to form a low frequency coloration in the sound. At its worst, it is
a grossly exaggerated fullness, which tends to obscure detail and distort the natural tonal
balance of the speaker system.
Occasionally, however, there is just enough resonance to give a lit tle added warmth
to the sound – an addition some listeners prefer. Careful placement of loudspeakers in the
room can dramatically reduce the speakers' destructive interaction with low frequency
modes. ASC Tube Traps™ are ef fective in reducing some of this low frequency room col-
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