The performance in terms of sound insulation of an enclosure (acoustic hood) - structure enveloping a sound source (machine), designed to protect the environment of this sound source (machine) - is very frequency dependent and is primarily related on the one hand to the performance of acoustic insulation panels (characterized by their sound reduction index) and also where appropriate to that of the silencer (for ventilation) and also to the number and to dimensions of cuts and openings, and on the other hand to the sealing imperfections and to structure born (bridging) sound transmissions.

This performance can be expressed in terms of difference (with and without the enclosure) of overall A-weighted sound pressure levels or of sound pressure levels in octave bands at specified locations (such as maximum value at 1 m from the walls of the enclosure, average value on an enveloping surface, value at a workplace) - also known as acoustic pressure reduction - of in terms of difference of overall A-weighted sound power levels or of sound power levels in octave bands of the enclosure - also known as acoustic power reduction or insertion loss od the enclosure-

For orders of magnitude (and with respect to a noise spectrum like "pink noise"), a level difference of up to 10 dBA can usually be obtained without special requirements, while a level difference from 10 to 20 dBA requires a standard enclosure without important leakage, while a level difference of 20 to 30 dBA requires a standard enclosure with sealing joints carefully implemented, a soundprrofing floor and a resilient mounting (enclosure with a vibration control system), and while a difference of 30 to 40 dB involves high performance enclosures carefully designed and installed (a level difference even higher shall involve a special construction).

The prediction of acoustic performance (for airborne sound) of an industrial enclosure can be performed with the simulation software SILDIS®®.

Verification of acoustic performance of an enclosure can be conducted (depending on the case) in accordance with the standard ISO 11546-1 Acoustics - Determination of sound insulation
performances of enclosures - Part 1: Measurements under laboratory conditions (for declaration purposes) or in accordance with the standard ISO 1546-2 Acoustics - Determination of sound insulation performances of enclosures - Part 2: Measurements in situ (for acceptance and verification purposes).

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