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22
Acoustics
Magazine reviewers and audio system owners spend much
time critically appraising speakers and other audio compo
-
nents. Unfortunately, a phenomenon that has a very large effect
upon sound is not easily judged or changed. That effect is the
ACOUSTICS of the environment in which you are listening.
Room acoustics is a complicated subject about which entire
textbooks have been written. We simply want you to be aware of
a few basics that have a direct effect on real time audio analysis.
As you probably learned in high school, sound travels in
waves. In an audio system, these waves are created by the speak
-
ers. Like waves in a pond cre
-
ated by a splash, sound waves
emanate from the transducers
(speakers) and spread out into
the room. If your room were
infinitely big, that’s all there
would be to it. But just as
waves in a pond reach the bank
and reflect back, sound waves
bounce off walls, ceilings, and
floors, reflecting, reinforc
-
ing and canceling each other
as shown in the figure above.
Since sound is energy, the way
it reflects depends upon the
angle of the surface, the type
of material and the frequency
of the sound wave. Because
your listening position is likely
to be towards the back of the Free Field (waves shown in the
diagram), you also get part of the reflected Reverberant Field as
well.
Now we add the next set of complications: Different fre
-
quencies of sound have different wave lengths (a function of fre
-
quency and the speed of sound). Each frequency’s wavelength
contributes differently to the Free and Reverberant Fields
because they are different sizes. For example, a 32 Hz bass note
has a wavelength of 35 FEET, while a 16,000 Hz note has a
wavelength just under a tenth of an inch. Tiny treble waves can
be caught and neutralized by draperies, carpeting, upholstered
furniture and gangs of indolent Persian cats…while gigantic
bass waves simply slosh back and forth in the room.
Room interaction
Room Acoustics
