Acoustic Insulation

In
a well furnished lounge, the sound of a handclap dies out much
sooner than in an empty room. The former has a shorter
reverberation time than the latter because it contains more sound
deadening materials.

Studios
for speech and music should have a reverberation time of about half
a second and this is obtained most economically by the use of
Fibreglass insulation.

For
every 3 – 4 m3 of studio volume, use 1m2 of 100mm thick Fibreglass
having a density of 24 kg/m3. Fit in patches distributed over the
walls and ceiling.

Church,
School and Recreation Halls must compromise between speech and
music. A reverberation time of about 1 second for an occupied hall
is acceptable. It is often suitable to treat the rear wall only
with 2 x 50mm layers of Fibreglass Aerolite compressed to 75mm,
covered with Hessian, and finished off with wooden battens spaced
to provide 30% open surface area.

The
Fibreglass does not act as an additional insulator but quickly
absorbs the sound in the interspaces

N.B.
Tests have shown conclusively that it is the thickness of the
insulation, and NOT the density, which is important in dry-wall
partitioning.

Fibreglass
is a highly efficient SOUND ABSORBER and equally good HEAT
INSULATOR

Aerolite
on the ceiling not only reduces sound penetration of the
roof-ceiling combination, but also keeps out summer heat and keeps
in winter warmth.

Sound
striking a hard surface is bounced off. When it strikes a layer of
Fibreglass, it enters the material and encounters friction, which
changes the sound energy into heat energy.

A
sound absorption co-efficient of say 0.95 implies that 95% of the
energy is absorbed. At the highr frequencies the co-efficient can
be greater than 1 – the material has a “sucking” effect
so that more sound reaches it than would fall on the same area if
it were hard.

The
high notes are absorbed more than the low ones. This is typical of
a fibrous sound absorber and need not necessarily be a disadvantage
because the ear is less sensitive to the low frequencies while the
high frequency components of noise are annoying.

Test
results prove that low frequency absorption increases appreciably
with increased thickness. To absorb all frequencies well, use a
thick layer of Fibreglass. If high frequency absorption is
required, a more economical thinner layer could be sufficient.

Pink
Aerolite in rolls is very well known as a ceiling insulator for
heat. Because of its ready availability and excellent sound
absorption, it is also widely used to absorb sound. The denser
versions of Fibreglass are supplied in Batt form. For critical
applications, such as Broadcasting and Recording Studios, batts of
different densities are often used. A higher density can of course
be had by compressing Aerolite. The basic fibres are the same, the
higher density types being more compressed.

Fibreglass
sound absorbing materials can be covered with sound transparent
materials to suit the surroundings. Dyed or natural Hessian, or
“Shade netting” prevents erosion of the fibres and would
be minimum cover.

In
Air-conditioning plant rooms, wire mesh could be added for extra
protection and faced with “Sonic-liner”

“Peg
board” is also often used.