Recording - September 2013 - 40

So you’ve been put on notice—the sound from your studio
or music room is bothering others and you’ve been told it
has to stop. It could be family members, it could be neighbors, it could be the local gendarmerie doing the talking, but
the message is clear and noncompliance is not an option.
But what if you make your living with sound? Talk about
being stuck between a rock and a hard place! You can’t
shut down, but you have to fix the problems. The good news
is that there are things you can do to reduce or eliminate
sound leakage and improve the acoustic isolation of your
room, and many of those fixes are simple and easy to do. A
little bit of home improvement skill will go a long way
here. (And by the way, these remediations can also be
applied to a home theater.)
How sound gets from here to there
The first step in conquering this problem is to understand how sound leaks out. There are three paths that
sound can use to migrate to places where it is not welcome.
First and foremost is airborne leakage, where sound
energy in the air leaks through openings. Because sound
is created by small changes in air pressure, even the smallest opening will leak—any opening in your room is a place
for sound to get out! And it doesn’t take much of an opening to let a lot of sound out. This means doors, windows,
gaps in the wall, holes for electrical outlets and switches,
openings from age-related changes in a building—these
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RECORDING September 2013

all leak sound. They are referred to as “penetrations” in
the acoustics industry.
But sound can also leak from your room through its
physical structure. With the second path, sound strikes a
wall, imparting some of its energy to the surface panel.
This makes it vibrate. This energy is then transferred
through the structure of the wall framing to the panel on
the other side, which then vibrates. This happens
through something you may have heard of in a school science class—the Newtonian laws of physics, for conservation of momentum and energy in a mechanical system.
You’ve probably seen these laws of physics at work in a
popular executive toy called “balance balls”, known more
formally as “Newton’s Cradle” (see Figure 1). Five or six
metal balls are suspended in a cradle, then the ball at one
end (call it Ball 1) is lifted and released, striking Ball 2.
Balls 2, 3, 4, and 5 don’t move, but ball 6 flies up and out.
Even though no motion is seen in the middle balls, the
kinetic energy still transfers to the sixth ball, where,
unfettered, the energy is released as motion. (Visit
http://en.wikipedia.org/wiki/Newton%27s_cradle to learn
more.) This is how sound travels through a wall’s structure.
Things may not be moving, but they’re still transferring
energy, in sufficient amounts to be significant.
The third path is for sound from a source to travel by
means of direct contact with the room’s structure. This is
what happens when a speaker or subwoofer is sitting on

http://en.wikipedia.org/wiki/Newton%27s_cradle

Recording - September 2013

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