By Alan Lofft-Axiom Audio
Last month's Part One
on home theater soundproofing received an excellent response, including
rather vociferous discussion on other sites (and in emails to me),
encouraging the use of a substance called "Green Glue" in place of
silicone caulk. Further research indicates there is a range of various
soundproofing caulks and glues available from a variety of vendors at
widely varying prices. To sum up, it's the sealing properties and
elasto-viscous nature of these materials that all help, but
do-it-yourselfers should be cautious about some extravagant claims made
for some of these materials.
Specialty Materials
One reader sent along a link to www.quietsolution.com
which markets a popular specialty soundproofing drywall called
QuietRock, comprised of three layers of viscoelastic, ceramic and
gypsum material. QuietRock's QR-525, which incorporates these layers,
claims to be remarkably effective -- one 5/8-inch layer of it is said
to be the equivalent of up to eight layers of standard drywall and
achieve STC ratings of "up to 72". It's certainly worth exploring these
and other options.
That said, there is still no substitute for the tried and true construction techniques outlined in Part One
-- staggered-stud walls with double layers of drywall on each side,
interior wall cavities loosely filled with sound-deadening insulation,
solid-core doors (or double doors), weather-stripping, using dissimilar
materials and/or air spaces and so on.
The Room Within a Room
But
there is one soundproofing solution that tops them all -- building a
room within a room, which is derived from methods used to isolate
recording studios and concert halls from all extraneous sounds and
rumbles. Both the Glenn Gould studio in the Canadian Broadcasting
Corporation's Toronto broadcast facility and Zankel Hall, the recital
hall that is part of the Carnegie Hall complex in New York, isolated
the recital halls from streetcar and subway rumbles, respectively, by
constructing an interior hall that rests on huge rubber dampers. This
room within a room technique not only excludes all exterior sounds but
also prevents sound from within the halls themselves from escaping to
other performance spaces in the buildings.
The Double Floor
You
can use a similar technique by building a double floor (see
illustration below) that rests on half-inch-thick rubber mats (look for
these from specialty suppliers). The double floor with 3/4-inch plywood
on top and bottom, and fiberglass insulation between the 2 x 4 studs,
supports the inner room, which also uses studded walls with drywall on
both sides and sound-deadening fiberglass insulation within the wall
cavities. A 6-inch air gap between the walls of the inner room and the
outer room is sufficient to greatly reduce sound transmission.
Carefully compute the dimensions of the inner room, taking into account
the airspace between the inner and outer walls, as well as the actual
thickness of the inner and outer walls, to come up with a consistent
air gap of 6 inches. The dimensions of the inner room will,
consequently, be much smaller than that of the outer room. The studded
walls of the outer room should also use drywall on both sides.
Specialty
sound-deadening insulation products are available for use within the
walls and include such brands as Owens Corning QuietZone and Roxul Safe
'n' Sound.
Since you've constructed an inner room and an
outer room, it will by nature have two doors, which will be very
effective in keeping sound from escaping. You should consult a
specialty sound contractor for details on sound-deadening ventilation
techniques that can be applied to the hot and cold air supply and
return ducts as well as methods of wiring that prevent sound leaks to
the outside.
It is beyond the scope of this article to go
into precise carpentry techniques of floor, wall, joist, stud and
header construction, but abundant material is available on the Web and
in books. Here are some links to other sites and products that may
prove helpful in your soundproofing endeavors:
- http://www.quietsolution.com
- http://www.roxul.com/sw47802.asp
- http://www.owenscorning.com/quietzone/products/products.asp
