10.3 - How do I soundproof a room?
Description
This article is from the Audio Professional FAQ, by with numerous contributions by Gabe M. Wiener others.
10.3 - How do I soundproof a room?
Despite what you may have seen in the movies or elsewhere, egg crates
on the wall don't work!
First, understand what's meant by "soundproofing". Here we mean the
means and methods to prevent sound from the outside getting in, or
sound from the inside getting out. The acoustics within the room are
another matter altogether.
There are three very important requirements for soundproofing: mass,
absorption, and isolation. Actually, there are also three others:
mass, absorption, and isolation. And to finish the job, you should
also use: mass, absorption, and isolation.
Sound is the mechanical vibration propagating through a material. The
level of the sound is directly related to the size of those
vibrations. The more massive an object is, the harder it is to move
and the smaller the amplitude of the vibration set up in it under the
influence of an external sound. That's why well-isolated rooms are
very massive rooms. A solid concrete wall will transmit much less
sound then a standard wood-framed, gypsum board wall. And a thicker
concrete wall transmits less than a thinner one: not so much because
of the distance, but mostly because it's heavier.
Secondly, sound won't be transmitted between two objects unless it's
mechanically coupled. Air is not the best coupling mechanism. But
solid objects usually are. That's why well isolated rooms are often
set on springs and rubber isolators. It's also why you may see
rooms-within rooms: The inner room is isolated from the outer, and
there may be a layer of absorptive material in the space between the
two. That's also why you'll also see two sets of doors into a
recording studio: so the sound does not couple directly through the
door (and those doors are also very heavy!).
If you are trying to isolate the sound in one room from an adjoining
room, one way is to build a second wall, not attached to the first.
This can go a long way to increasing the mechanical isolation. Try
using two sheets of drywall instead of one on each wall, and use 5/8"
drywall instead of 3/8", it's heavier.
But remember: make it heavy, and isolate it. Absorptive materials like
foam wedges or Sonex and such can only control the acoustics in the
room: they will do nothing to prevent sound from getting in or out to
begin with. [Dick]
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