Unfortunately, there is no way to eliminate the effects of standing waves completely. The
best that can be done is to minimize their effect through a variety of strategies.
STANDING WAVE SOLUTIONS: ROOM RATIOS
In new construction, the best way to minimize the audibility of standing waves is to plan
for an even distribution of them, so that their effects do not “pile up” on top of each
other. In this regard, the ratios of room dimensions are the critical factor. Rooms having
equal dimensions are the worst, since the standing waves in all directions reinforce one
another. Room dimensions which are even multiples of one another are also to be
avoided where possible.
STANDING WAVE SOLUTIONS: SPEAKER PLACEMENT
Speaker placement also has an effect on standing waves and their audibility. In particu-
lar, placement of any speaker (including subwoofers) where two walls and the floor
meet will tend to stimulate all of the available standing waves, causing the most irregu-
lar response. The displacement required to minimize a particular standing wave
depends on its frequency, with lower frequencies requiring more movement owing to
their longer wavelengths. As a result, minimizing colorations due to standing waves
often requires significant adjustment of subwoofer placement. Leave yourself some lati-
tude with regard to subwoofer placement when planning your system—the final adjust-
ment will probably have to be done on something of a trial-and-error basis.
STANDING WAVE SOLUTIONS: ABSORPTION
In theory, it is possible to damp standing waves with absorptive material. The difficulty is
that the thickness of the absorptive material would have to be approximately one-half
the wavelength of the lowest frequency requiring damping. This means a five-foot thick-
ness of fiberglass would be required in order to damp everything down to 100 Hz—not
very practical.
Standing wave energy tends to be concentrated in the corners of rooms, which is why
these are the worst places for subwoofers. Because of this fact, it may be possible to
break them up somewhat by “breaking up” the corner. This can be accomplished by
placing a column of thick, absorptive materials in the corners (covered by acoustically
transparent cloth, of course). The column ought to be at least a foot on a side, and run
from floor to ceiling. A variation on this theme is to run an absorptive panel diagonally
across the corner, leaving open air space behind it. Neither of these techniques is more
than a partial solution, at best, but they are easily tried and sometimes quite effective.
31
