On Sat, 28 Apr 2007 15:40:17 -0500, someone wrote:

Everything I've ever read indicated that regular fiberglass was a poor
noise insulator. Add to that that the studs still connect the two
sides of the wall and this one just smacks of scam.

The three factors to reduce sound transmission are mass, separation
and (preventing) infiltration. Fiberglass only helps some, but it is
a lot better than just an open cavity.

Where we have some adjoining bedrooms, we have separate parallel stud
walls, and "sound board" under the sheetrock on each wall. Bedroom to
bedroom is a critical area since the person trying to sleep will
likely have their room quiet, so will more easily be able to notice
any sound coming through the wall from the next room.

Where two of these bedroom are next to a "den", we also have sound
board under the sheetrock (single wall only). However this is of
limited effectiveness as it is udnermined by this being the wall with
the bedroom doors. More sound likely infiltrates under the little
crack under the door than through the entire wall itself. This type
of thing is often quite noticeable in hotels. The wall between rooms
may be massive (concrete block) but there is a gap under the door big
enough for them to slide newspapers through, and you can easily hear
the conversations of anyone passing by in te hallway.

The fiberglass helps with some mass. If there were openings in the
wall skins (such as cutouts for electrical outlets) it would also help
cut down on the infiltration by muffling the direct path from outlet
to outlet (don't put them back to back in the same stud space).

The fiberglass itelf doesn't help with through transmission from the
single studs bridging the cavity. BTW, to cut down on through-stud
transmission, if you don't have room for two full walls, use a single
2x6 sole and plate, and then stagger 2x4 studs alternating to each
side. There is still through transmission through the sole and plate,
but much less as the studs now don't go through.




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