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MEEF - Articles - Rockwool  (1) (2) (3) (4) (5) (6) (7) previous page
 

Acoustic applications of mineral wool
 

Uses - Acoustic InsulationUnwanted 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:

  • Level

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

  • Duration

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

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:

  • Reverberant sound (echo) when within spaces; and

  • impact and airborne sounds when in adjacent spaces to the sound sources.

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

Uses - Acoustic InsulationThis 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

Uses - Acoustic InsulationOtherwise 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:
 

  1. The sound absorbency of any cavities (concerned with airborne sound).

  2. The mass of the separating element (concerned with airborne sound).

  3. The structural isolation of elements within the construction (concerned with impact sound).

  4. 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.

courtesy:  

 
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