Natural Science Forum / Physics / Acoustics / August 2007

    That will provide about STC 40-45.

    Coincdence transmission will pass 300-400 Hz (vowels), so
intelligibility will be almost nil.

    Probably naturally amplifies about 1 kHz

    Add a second barrier wall spaced a some inches from the existing wall;
no contacts with the existing wall. Two layers of gypsum board on wood
or metal studs will do. Figure an air gap between the concrete and gyp
surfaces of at least 6" (150mm) for an overall room space loss of a
180mm with along that common wall. The 6" void must be filled with glass
fiber, or any fiber (NOT foam) used for thermal and sound absorption.
Caulk the entire outside perimeter of the added wall. Paint to suit.

    This will provide excelent sound reduction except in one instance; a
resonance at 34 Hz. The lowest common drum-beat frequency component in
rock music is in the 40 to 60 Hz range, sometines 30 Hz. The concrete
does fairly well at reducing that, so overall, you may be satisfied.

    It is generally but a fancy name for drywall. In this case, this is an
Australian version of "Quietrock" which avoids the 2,000 Hz coincidence
transmission in drywall. But concrete does this well anyway, so it is
not called for in your case. The drywall (aka plaster board or gypsum
board) doe sjust as well or better at less cost and effort.

    Correct; the air gap is VITAL.

    Probably naturally provides mechanical amplification around 1,000 Hz
that promotes speech intelligibility.

    Angelo Campanella

The barribioard is not just "glued on". As a "glue on it would add a
little more damping and a tiny increase in mass - and could either
increase or decrease you problem.

It is a second wall that is required in your situation but much depends
on the current construction of the building.

Rather than construct a second offset steel stud frame wall faced with
high density gypsum plasterboard (16mm Fyrchek or 16mm Firestop or 16mm
Fireshield or 13mm Soundchek), this is a offset steel stud framed wall
with a sheet of high density gypsum plasterboard consisting of a
laminated 13mm sheet made from laminating two 6mm gypsum plasterboard
sheets together with an interlayer - called  "barriboard". The
configuration in your situation (with an existing 100mm concrete wall)
appears to be an untested configuration.

E-mail me back and I'll head you in the right direction.
Where in Australia are you?