Recording - March 2015 - 15

3. Diffusion is the scattering of sound (shown at left). This can be done with a
variety of treatments, including the polycylindrical diffusor (shown at right).
other as they reflect between room surfaces, thereby adding to each other. These
are resonances, which can cause sonic colorations. Each dimension of a room equals
the wavelength of its resonant frequency,
plus its multiples.
In reflective rooms, the resonances can
store speakers' energy like a sonic battery.
This stored energy lingers beyond the other
sounds' decay, and then is released once
the stimulus stops. This gives the room's
sonic signature a coloration at that frequency, rather like how an equalizer works.
Problem #5: Surging Sound Leakage
How many times has someone complained about the "noise" coming out of
your studio? If you have a home studio,

sound may be leaking into another bedroom and disturbing someone sleeping, or
the living room where someone is doing
homework or watching a show. No one
really wants to be disturbed by something
they're not participating in. In multi-room
music or post production facilities, it's particularly important to control sound leakage so that one room's work isn't contaminated by what's going on in another room.
Leakage can be a particularly troublesome issue. Any holes or crevices in a
room surface can be the source of leakage. It may be the gap hidden under an
electrical cover plate, a space between
the drywall and floor under the baseboard, or the gap between the drywall
and door frame under the trim molding. In

a residential structure, that spare bedroom
you use as a studio can have lots of gaps
and holes. These structures are built more
for looking good than for containing
sound leakage.
However, sound can also leak through
the physical structure (framing, etc.) of the
room, and once it's in there you can't get
rid of it. Let's say you have a speaker that
sits on the floor. Some of the speaker's
vibrations get into the cabinet. These
vibrations cross easily from the cabinet
into the floor and into the rest of the building, where they can travel great distances.
A great demonstration of this is a device
called a Newton's Cradle. You may know
this better as an executive toy called "Balance
Balls". Five balls are suspended in a row on
a frame. If you lift and release the ball at one
end, it strikes the second ball, which doesn't
move. Nor do balls three and four, but ball
five flies out, as if by magic. Check out the
"Newton's Cradle" entry in Wikipedia for an
explanation and animation.
This is how sound energy travels through
the solid structure of a home: the energy is
transmitted, without any actual movement.
Yes, some of it is dissipated as heat, but it's
a very small amount; solids transmit sound
very efficiently. Eventually that energy finds
something loose like an unsupported drywall
panel or a lighting fixture, causing it to
vibrate or rattle.

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Recording - March 2015

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