Every company that makes or installs PVC windows or doors in your town
will have 1/8 inch thick PVC sheet, typically in a 20 inch width. They
use it to make PVC "returns" on the window they install. Often, the
walls of the buildings they install their windows into are thicker than
the windows themselves, and so they need something to make up that
difference between the window frame thickness and the wall thickness.
If your intention is to reduce the noise from your air conditioner, then
insulation isn't going to help much. When a sound wave hits a wall (for
example) the sound wave DOES NOT travel through the wall. Instead, the
wall moves slightly as a result of the sound wave and that motion
recreates a second sound wave on the other side of the wall. It's that
recreated wave you hear, not the original.
It's this simple as dirt method of sound propogation through walls
that's the basis of the MASS LAW of Acoustics. The mass law says that
for every doubling of the weight of the wall (per square foot) OR for
every doubling of the frequency of the sound wave hitting the wall, the
amplitude of the recreated sound wave on the other side of the wall is
reduced by 6 decibels, or to 1/4 of it's former amplitude.
That's because the more massive the wall, the less it moves in response
to the sound wave hitting it, and that means the amplitude of the
recreated sound wave is also reduced. Also, the more massive the wall,
the less able it is to can change it's direction of motion quickly. So,
the higher the frequency of the sound wave hitting the wall, the less
capable the wall is of reproducing that sound wave. In the ultimate
instance, the inertia of the wall would prevent the wall from responding
to a high frequency sound wave at all, and the result would be silence
on the opposite side of the wall.
So, to stop the noise from your air conditioner, a smarter gameplan
would be to install heavy shutters on that window that could be closed.
You want to avoid having air paths through the shutters that the sound
could travel through, so your shutters would either be solid and block
the light, or you could have the shutters made out of 1/2 inch thick
Also, have curtains made for that window from the thickest and heaviest
drapery you can find. Almost certainly MOST of the sound you hear is
coming through the closed glass window, and so that's where you should
concentrate your efforts at reducing the noise. Put as much mass
between you and the air conditioner as you can, and that will stop more
noise than your insulation idea.
'ARCHIVED - Sound Transmission Through Building Components - IRC -
NRC-CNRC' (http://tinyurl.com/c2xmqm3 )