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SOUND
INSULATION
This section provides only an introductory guide to control of noise using
glass.
It is important to note that laboratory sound reduction results as shown,
may differ from actual site conditions and results. Careful consideration
should also be given to the frequency and intensity of the sound, framing
types and construction, window surrounding/building material construction
and any specialised acoustic requirements.
As a general rule, increasing mass will improve sound insulation. Brick
and concrete walls have stronger sound insulating values because they are
of greater mass when compared to glass. But because we need glass to see
through, to provide natural daylight and enhance a buildings look and appeal,
the need for greater sound control when using glass becomes more important.
Sound originates from something that vibrates which generates changes in
air pressure. FREQUENCY is used to refer to the number of vibrations or
changes in air pressure per second.
The value given is usually expressed as hertz (Hz) (i.e., 750Hz). Different
sounds produce different frequencies. Traffic noise as an example, produces
sounds most intensely in the lower frequency range. The INTENSITY or LOUDNESS
of a sound is of most concern to people. The loudness of a sound is rated
as DECIBELS or ‘dB’. Tables 1 and 2 list general sound information
and sound reduction information using glass.
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When
referring to these tables, the following points should
be considered:
The
Human Ear
 under
typical field conditions the ear cannot detect a change
of 1 - 2dB;
the
ear will not pick up a change of 3dB if there is a time lapse
between the two sounds and they are of moderate or low intensity;
a
change of 5 - 7dB can always be detected;
for
every 10dB increase/decrease in intensity we perceive the
sound as being a doubling/halving of the noise level.
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GENERAL
SOUND INFORMATION
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SOUND PRESSURE LEVEL
| Noise
level (dB) |
Example
of Noise |
| 110 |
Nearby
riveter |
| 90 |
Noisy
factory/loud street noise |
| 70 |
Average
street noise |
| 60 |
Average
office noise |
| 50 |
Average
conversation |
| 40 |
Quiet
radio/private office |
| 30 |
Average
auditorium |
RECOMMENDED
DESIGN SOUND LEVELS*
| Activity
area |
Satisfactory
(dB) |
Maximum
(dB) |
| Residential
recreation area |
30 |
40 |
| Bedroom |
25 |
30 |
| Classroom |
35 |
40 |
| Commercial
offices |
40 |
45 |
*AS2107 Acoustics – Recommended design sound levels and reverberation
times for building interiors 1987. |
NOISE
REDUCTION COMPARED TO 3MM FLOAT (IN STL)
| Glass
thickness (mm) |
Reduction
(dB) |
| 6 |
3 – Barely
noticeable |
| 6.38 |
5 – Clearly
noticeable |
| 6.76 |
7 – Clearly
noticeable |
| 10.38 |
11 – Halving
of original noise |
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The
definition of noise
is ‘an unpleasant, disturbing or unwanted sound’. Noise sources vary
greatly from traffic noise to busy office environments. Noise is a form of pollution
which can impact adversely on people’s mental and physical health. |
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