On 8 Jan 2007 08:20:00 -0800, "JimmyD" wrote:

Hello All,
I'm in the process of finishing my basement. The ceiling is (will
be) a drop ceiling. The rafters above the drop ceiling don't have any
insulation in them. The basement is where my home theater will be, so
sound insulation is of high importance. My local hardware store carries
Johns Mansville insulation, and I decided to get kraft faced insulation
for ease of installation. I was wondering what thickness of insulation
to buy. The rafters are 9 inches deep (and 15 inches wide). The two
thickness of insulation I was looking at are 8 1/4 and 10 1/4. I didn't
know if it was better to go with the 8 1/4 and have a small gap or go
with the 10 1/4 and compress it a bit when I install it. Here's the
brochure for the insulation if that helps:
http://www.jmhomeinsulation.com/pdfs...28c77 7520642
. Also, I live in South Dakota, if that makes any difference.



There are really only four tricks to limiting sound transfer:

Closing off air gaps, decoupling surfaces, weight, and
getting rid of large flat reflective surfaces.

So you start by spraying a thin layer of urethane foam
on the underside of the floor. This seals any open
air passages, adds a tiny but of mass, and creates a
bumpitty surface to break up sound. Then you stuff
some asphalt roll roofing into each rafter bay,
holding it up with wire. After that, if you have
the headroom, you stick resilient-channel crosswise to
the joists (cheap, but takes a lot of space) or
add 2x6 joists between the existing floor-joists,
only with the bottom edges 3/8" lower, and
attach 1 layer of homasote 440, and one layer of
1/2" sheetrock to that.

If, for some reason, you must use a suspended
ceiling, invest in a great many extension springs,
(tearing apart certain kinds of bed is a good way
to find those) And cut up a bunch more squares
of that asphalt roll-roofing to put on top of
the tiles. to add weight. Use the heaviest
metal gridwork you can find.

If you have ceiling-mounted light fixtures,
move them to the walls, since they form a
pathway right past your sound-deadening
structure.

Remember that you are no longer going to be
able to hear things like telephones,
fire-alarms, and doorbells through the
floor, so you'll want some sort of repeater.

--Goedjn