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Reduction figures:
Airborne sound insulation is denoted:
Rw = weighted sound reduction as measured in laboratory
R'w = weighted sound reduction index measured in buildings
Laboratory measurements will typically be 4-5 dB better than measurements made in buildings for the same construction.
Sound reduction (explanation):
1 dB
A chance, which is accurately that big that it can be recognized.
3 dB
An appreciable change, which is clearly to hear.
-corresponding to a change of the hearing impression of 20%
-corresponding to theoretically halving of the sound pressure.
6 dB
A significant change, which is very clearly to hear.
-corresponding to a change of the hearing impression of 35%
10 dB
A very significant change, which man perceives as a halving of the sound.
-corresponding to a change of the hearing impression of 50%.
. . . . . . . . . . . . . .
Partitions.
The sound reduction for example achieved through a plate-lined wall depends on several factors:
1. The sonic properties of the plate lining.
2. The distance between the plates.
3. Whether there is contact between the plates for example through uprights, or if the plates stand independently.
4. Whether the cavity is uninsulated or if it is insulated with for example 100 kg Bonded Foam (RE100).
The primary function of the insulation is to reduce the acoustic connection between the two walls, and thereby prevent, that the sound pressure in the cavity is enlarged.
In order to damp, a possible resonance effect in the cavity there will be insulated with a sound absorbing material, as for example 100 kg Bonded Foam (RE100).
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Damping of machine noise
A Combination that works!
If you embed a noise source (for example a noisy compressor) in a closed metal box, with a lining of for example 50mm RE100 insulation, then you will experience a very great reduction of the sound pressure (effect).
It is precisely a combination of an air-locking outer capsule (of e.g. steel) + a sound insulator (as e.g. RE100) which gives the maximum reduction effect!
Like that, a guard or an insulation material should never stand alone..!
Sectional view of a soundproofing box.
- Remember to find out if locks for air intake/extract are needed!
Soundproofing box made in 100% metal:
-if for instance you just lowered a metal box down on a noisy compressor that is without any insulating lining, you would only change the noise from the compressor. Principally the box would work as a bass speaker, and there would not be any real sound reduction.
Soundproofing box made in 100% insulation:
if instead you just used pure insulation material, the situation would improve a little, because of the sound absorbing ability of the material.
However, the noise (the air particles) would in some degree go through the insulation, and thereby let the noise pass through.
A Combination that works!
- If you want the optimal sound insulation, then you should take notice of the following four important elements:
1.
You should build a soundproofing box, made from a metal-, wooden- or plaster plate - and the inner lining should be 40-50 mm soundproofing Bonded Foam.
2.
You have to secure, that there are no leaks in the lining and the plates of the box. Even tiny air rifts can course that the noise will penetrate.
3.
You have to secure, that the compressor, if such, is not mounted direct on a concrete floor, but is mounted on e.g. rubber feet or another vibration damping material. this will secure that vibrations and structure borne sound are not spreading to other rooms.
4.
Casted piping, which may be mounted direct on the compressor can also be the source of annoying structure borne sound. Piping should therefore be mounted with rubber bushings etc.
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