On Sun, 24 Feb 2019 10:05:32 -0800 (PST), Davej
wrote:

Found an interesting Youtube video on practical wall construction. Anyone here have experience with this sort of thing?

https://www.youtube.com/watch?v=GLjhrXFo0Kw
instead of 2 layers of drywall. use mdf for the first (inner) layer
- much higher density. resiliant channel or accoustic glue are both
good. Isolating the second wall from both floor and ceiling helps.
Mount the wall to the floor using a "dri-core"base - doen't hurt to
use it between the top sill and the ceiling joists above either.

The difference between rock-wool and fiberglass IS significant.

The two important things are MASS and ISOLATION. - and of course
isolation includes ELIMINATING gaps.

As far as the heat ducts are concerned just insulate well around them
and make use of "baffling" - don't have as traight run from one room
to another make sure the sound needs to go around a few corners and
make sure to "damp" any flat sided ducts. to absorb as much sound
vibration as possible. A large thin rectangular duct can act as an
AMPLIFIER of sound by re-reflecting it. Damped, the sound does not
bounce.

Even installing a second stud system of 2X2 or 2X3 staggered between
the 2X4 studs fastened to the same sills, spaced out 1/2 inch so the
drywall is fastened to different studs on each side makes a big
difference without taking up as much space. - and using accoustic
cement to fasten the drywall instead of screws or nails also helps
decouple the sound. If the joists run between the 2 spaces instead of
parallel as shown in the video, install baffles between the joists -
tight fitting MDF or plywood covered with a foam-board works good -
even just 2 inch foam board is a lot better than nothing - seal the
joints between the baffle and the joists with spray foam or a good
relilant caulk. For the ceiling, building a second framework,
attached to the studs of the INNER wall and not to the joists above is
also a good idea. a few hanger wires mid-span attached to the joists
above don't degradethings very much if required to prevent ceiling
sag. The ceiling "joists"only need to support the drywall and any
insulation - and can be "staggered" between the existing joists to
reduce the loss of room height..

If using a complete second wall system the second ceiling framing can
be connectes only to the inner wall, and the inner wall can be
completely "decoupled" from the ceiling. That's how a friend's home
recording studio was done. - with the floor sitting on 2 inch
"styrofoam SM) , and the walls built on top of that, withthe ceiling
attached to the inner walls only, and the gap filled with blown
rock-wool. A bomb could go off in the next room and you wouldn't hear
it (double doors too,of course)