Acoustic applications of mineral wool
 Unwanted
sound or 'noise' will create an environment which inhibits human contact
and privacy. This includes the effects of noise both within spaces and
its passage between adjacent spaces that people occupy.
Noise may range from being a
distracting irritation to causing actual physical damage and loss of
hearing. More than 53 million people in Western Europe suffer from the
effects of exposure to noise above 65 dB(A). At work, 37 million people
are exposed to excessively high noise levels. The cost of treating
health problems directly related to noise runs into many millions of
Euros annually.
Because of their particular
structure, mineral wool insulating materials provide a highly effective
barrier to noise which benefits the environment.
Specific products aimed at
acoustic treatment using mineral wool include acoustic ceiling tiles,
acoustic slabs, partition cavity filings, wall linings and floor/roof
level sound insulation and absorption. For example, the roof of the new,
Sir Norman Foster designed, Hong Kong airport is insulated with over
300,000 square meters of mineral wool roof boards to provide passengers
and workers with a quiet and pleasant environment.
Main applications include
ceilings for offices, public buildings, hygienic ceilings for hospitals,
laboratories and kitchens and sound absorbing ceilings for industrial
facilities.
The nature of sound
There are
three factors that affect people's experience and perception of sound:
Sound levels are expressed in
decibels (dB). A 10 dB increase corresponds to a perceived doubling of
the noise level. A 1 dB increase is the smallest audible change that can
be detected. The table indicates typical sound levels.
Typical sound levels
|
100 db |
Airports |
|
90 db |
Main line railways |
|
80 db |
Engineering working
conditions |
|
70 db |
Busy residential roads |
|
60 db |
Busy office |
|
50 db |
Living room with TV/
music playing quietly |
|
40 db |
Quiet office |
|
30 db |
Bedrooms |
|
20 db |
Recording Studios |
The hearing damage potential of
a noise is also dependent on the duration of exposure to it. Damage risk
is usually assessed on the basis of an eight-hour daily exposure cycle.
Frequency is expressed in Hertz
(Hz). Many noise sources contain a wide range of frequencies. However,
the human ear does not respond equally to sound pressure levels over
different frequencies. To compensate for the ear's varying sensitivity
sound is measured using dB(A), an internationally agreed weighting which
mimics the responsiveness of the human ear. Sound level meters
incorporate a filter for measuring in dB(A).
The passage of sound
The passage of sound also has
effects on people and structures which vary with the relative location
of sound sources. These effects are experienced and measured as:
Impact sounds include
footsteps, stamping on the floor and vibrating washing machines.
Airborne sounds include speech,
musical instruments and loudspeakers.
Effective solutions to the
problems posed by reverberant, impact and airborne sounds are based on a
clear understanding of the difference between sound absorption and sound
insulation.
Sound absorption
 This refers to the attenuation
of reverberant noise within the same room or area as the noise source.
This normally involves lining all or part of the room surface with a
sound absorbent material.
When a sound wave hits an
object some of its energy will be reflected and some absorbed. A
material's ability to absorb sound efficiently can be gauged from its
sound absorption coefficient. This is defined as the ratio of the sound
energy absorbed to the total sound energy arriving at a material's
surface. A material which absorbs 85% of the sound energy striking it
has a sound absorption coefficient of 0.85.
The structure of the fibres in
mineral wool materials makes them good at absorbing sound. Glass mineral
wool and rock mineral wool have similar sound absorption characteristics
and are equally good at improving the sound insulation performance of
constructions.
However, an increase in the
sound absorption within a space does not necessarily mean a
corresponding increase in the sound insulation between adjacent spaces.
There is no single direct link between absorption and insulation. Other
additional factors contribute to effective sound insulation.
Sound insulation
 Otherwise known as sound
reduction, this is the prevention of noise being transmitted from one
area to another. The ability of walls, partitions or floors to resist
the passage of sound energy through them is largely determined by four
factors:
-
The sound absorbency of any
cavities (concerned with airborne sound).
-
The mass of the separating
element (concerned with airborne sound).
-
The structural isolation of
elements within the construction (concerned with impact sound).
-
Flanking transmission.
The following examples show the
relative improvement in the sound insulation of a partition by adding
mineral wool insulation, increasing the isolation and its mass.
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