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Examples Of Noise Control
[1] Noise Control by Enclosure
A complete acoustic enclosure can provide noise reduction of 20 dB(A) or more.
An enclosure can be used to surround either the noise source or the person
exposed to it.
The walls and roof should be formed from a material having a SRI exceeding the
noise reduction required by at least 5 dB at all frequencies involved. To
prevent build up of reverberant noise within the enclosure an internal lining
of absorptive materials should be used – usually a minimum thickness of 50mm.
Direct vibration contact between enclosure and machine should be avoided by
using flexible couplings and seals. Small air-gaps can seriously detract from
the enclosure’s acoustic performance. Care is required when introducing
services such as cooling air, power, fuel or water to an enclosure, in order
to ensure its overall performance is not affected.
For all complete enclosures, attention to detail is vital to avoid weak
points. Doors must be fitted with flexible seals and spring closures or
compression latches. Windows must be constructed to provide the same SRI as
the remainder of the structure and consideration should be given to the use of
multiple glazing. In many cases a complete enclosure is not practicable, and a
partial enclosure may be necessary. In this case a lower Sound Reduction Index
is provided. The SRI becomes less important than the provision of an effective
sound absorbing lining. The fundamental design principle requires avoidance of
direct sight lines between source and receiver.
[2] Noise Control by Screens
In some cases, a simple screen may provide sufficient noise control, although
in general screens have very localised effects. A screen will reflect noise
and if lined with an absorptive material, will provide some further reduction
in the energy.
As in the case of partial enclosures, the screen may be constructed of a
relatively lightweight material, since the SRI required is not high. Noise can
diffract around obstacles and for maximum effectiveness, the screen should be
as large as possible and placed as close as possible to either source or
receiver. Screens should be both mobile and decorative.
[3] Noise Control by Room Treatment
Many noise problems result from the reverberant build up of noise within an
acoustically “hard” building. Reductions of the order of 4 dB(A) in
reverberant noise levels can often be achieved by the use of absorptive
ceiling and/or wall treatments.
The products that should be specified in these applications will depend to a
large extent on building type, i.e. industrial, commercial, etc.
In factories, Tap Quietair Baffles, see TAP Spec guide, suspended from the
roof or ceiling, effectively reduce reverberant noise.
In offices or commercial buildings where aesthetics are of importance,
reductions in reverberant noise levels can be achieved by installing a
suspended ceiling incorporating Taptiles and/or Tap Quietwall panels, see TAP
Spec guide. Floors may be improved by the use of Iso-barrier, see TAP Spec
guide.
The reduction in noise level depends on a number of factors, but in general,
for each doubling of effective absorbing area (or Sabin) in a room (effective
area or Sabin = area of absorber x absorption coefficient) a reduction of 3
dB(A) in the reverberant noise level may be expected. It must be emphasised
that this technique provides no reduction in the direct noise transmission
path and therefore accurate identification of these is essential.
[4] Noise Control by Combination of [1], [2] and [3]
The effectiveness of enclosures, screens and room treatment has been discussed
in isolation. However it may be necessary to use a combination of two out of
three or all three methods to obtain the correct noise control, e.g. Tap
Laminate, see TAP Spec guide.
[5] Noise Control by Partition Improvement
Many cases occur where existing partitions are acoustically inadequate. In
such cases it is usually possible to achieve improvement by: Stopping flanking
transmission, e.g. by sealing all gaps; providing a cavity lining of Taptiles;
or adding a secondary partition, separated from the original wall, again by
installing Taptiles within the cavity.
[6] Noise Control by Ductwork Lagging
Where noise is transmitted through the walls of ductwork, very effective noise
control can be achieved by an external application of 25-50mm Tap-wrap, see
TAP Spec guide, with a mass layer of at least 5kg/m˛)
A suitable external treatment is an application of Tap-wrap.
Where sound absorption in air conditioning equipment and distribution ductwork
is required, acoustic foam or melamine should be used.
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