Acoustical design is a very complex field.  Computer modelling is difficult as there are so many variables
absorbing batts as the acoustics were not what was envisioned.  As such, it can be imagined that
providing acoustical insulation is not straightforward either.  The crux of the complexity lies in the fact that
sound is transmitted over several orders of magnitude of frequency.  Although it is relatively simple to
choose a material that deadens the sound-waves at one frequency, to do so over an entire range,
becomes difficult.  
National Research Council of Canada Report is a good study on soundproofing.

There are two common metrics for measuring sound deadening
  • IIC – Impact Noise Class – this measures the impact noise of floors from things like walking.  This is
    the harder of the two to control and the one that impacts the human experience the most
  • STC – Sound Transmission Class – this is a more generic measurement – and refers to how much
    sound is being blocked
Higher numbers are better.  Both scales are logarithmic … 10 points of difference (ie: from a 50 to a 60) has
been equated subjectively to being "twice as quiet".

With sound transmission, it is all about the assembly. For low frequency noise, mass is a very important
parameter in effectiveness. With higher frequency sounds, the thickness of the insulation becomes more
important, leading one to use something lighter and airier. The test environment makes a big difference
on the numbers. For example,
Acousti-blok by itself might have a IIC of 60, but with tile (which is hard and
therefore transmits sound), it degrades to a 51. With hardwood, it would degrade less, to a 56. With carpet,
it would actually improve to a 67.

A parallel thought process to reducing the transmission parameters of the wall assembly, is not to allow
sound energy into the structure at all.  Resilient channel is a metal membrane nailed to the studs that is
"springy" onto which is screwed the gypsum.  The end result is that the gypsum is in effect physically not
in contact with the studs.   The resilient channel technique by itself typically adds 3 to 5 (or more) Sound
Transmission Class (STC) points to an otherwise identical wall or ceiling. For more information see
Resilient channel for soundproofing

Roxul AFB (Acoustical Fire Batt) is also worth considering.  It is a dense mineral wood similar to thermal
insulation (but green in color).  Not only does it have excellent fire retarding properties, but it also has
acoustical insulation values.   For more information, see

Ballpark economics is as follows for a representative 15 foot by 15 foot room
  • Acousti-blok is the most expensive - in quantity about $10 per square foot, installed.  With 225 sqft of
    ceiling at 60 sqft of walls (assuming 10 foot ceilings), the cost would be about $10 * 825 = $8,250
  • Resilient channel is about $0.30 per linear foot.  For a 10 foot wall, 24 inch on center, 6 channels are
    needed – with labor, it is about $5 per running foot.  The whole room would cost about $500
  • Roxul insulation is about $1 per sqft, which would put the cost for the room (walls & ceiling) at $1000

Effective acoustic insulation involves the co-ordinated use of a number of techniques, including Acousti-
blok, resilient channel and Roxul Fire Retardant Batts.  For the most challenging noise producers (ie:
drums) and the most sensitive containment areas, we recommend all three, as they work together.  For a
more cost effective approach, simply the combination of resilient channel and Fire Retardant Batts
provides a noticeable difference.