The efficiency for the reverberation control of a room (in workplaces, in a building for tertiary use, in a building for residential use ...) is very frequency dependent and is mainly related on the one hand to the performance of absorbent materials which constitute the partitions or of which are covered the partitions of the room (characterized by their absorption coefficient or by their Sabine factor) and also to their area, and on the other hand to the geometry of the room, to its volume, to its fitting density and to the level of its acoustic quality before soundproofing. In some particular cases (e.g. theatres, opera houses, concert halls, swimming pools), room occupancy and/or humidity rates are also taken into account.
Efficiency of the reverberation control of a room for what concerns reverberation time
The efficiency i.e. the performance can often be expressed in terms of difference (with and without the implementation of materials for reverberation control) of reverberation times or (for rooms with a particular use) of averages of reverberation times at some frequencies.
For orders of magnitude, a difference of reverberation time (or of averages of reverberation times at some frequencies) up to 40% can generally be obtained without special requirements after implementation of a suspended acoustical ceiling (or of a net of suspended acoustic baffles) in the case of premises where the ceiling height is low enough and where the partitions were highly reflective before soundproofing (e.g. concrete walls, metal deck roof) whereas a difference of reverberation time (or of averages of reverberation times at some frequencies) above that shall involve a special achievement that may necessitate the implementation of absorbing wall panels.
Efficiency of the reverberation control of a room for what concerns spatial sound decay
The efficiency i.e. the performance can sometimes be expressed (namely in workplaces) in terms of difference (with and without the implementation of the materials for reverberation control) of the sound level decay per doubling of distance from the source.
For orders of magnitude (and with respect to a noise spectrum like "pink noise"), a difference of decay of the sound level per doubling of distance from the source up to 25% can usually be obtained without special requirements after implementation of a suspended acoustical ceiling (or of a net of suspended acoustic baffles) in the case of premises where the ceiling height is low enough and where the partitions were highly reflective before soundproofing (e.g. concrete walls, metal deck roof) whereas a difference of noise levels decay per doubling of distance to the source above must involve special achievement that may necessitate the implementation of absorbing wall panels.
Efficiency of the reverberation control of a room for what concerns sound pressure level
The efficiency i.e. the performance can sometimes be expressed (namely at workplaces) in terms of difference (with and without the implementation of the materials for reverberation control) of overall A weighted sound pressure levels or of sound pressure levels in octave bands at specified locations well away from noise sources (in general: no value to a work station too close to a noisy machine).
For orders of magnitude (and with respect to a noise spectrum like "pink noise"), a level difference of up to 2 to 4 dBA can usually be obtained without special requirements at the end of implementation of a suspended acoustical ceiling (or of a net of suspended acoustic baffles) in the case of premises where the ceiling height is low enough and where the partitions were highly reflective before soundproofing (e.g. concrete walls, metal deck roof) whereas a higher level difference must involve a special achievement that may necessitate the implementation of absorbing wall panels.
In the particular case of industrial premises, the reduction of reverberated noise (resulting from the reflection of acoustic waves during their mean free path between the point of emission and the point of reception):
- does not change the sound level at a short distance from noise sources, when the direct acoustic field is preponderant; reverberation control works in premises (which may be required by regulation [1] cannot replace actions to reduce noise "at the source", e.g. by means of soundproofing enclosures to limit exposure to noise from shift workers in front of a noisy machine)
- is - in practice - almost nil as far as low frequencies are concerned (i.e. for the 1/1 octave bands with a central frequency of 63 Hz to 250 Hz), if only because the acoustic absorption coefficient is low at these frequencies
- does not exceed 5 or 7 dB (which is not nothing) in the best case
Services offered by ITS in relation to the efficiency of the reverberation control of a room
The services offered by ITS in relation to the efficiency of the reverberation control in a room are multiple (within the framework of engineering missions periodically evaluated and certified in accordance with the requirements of the ISO 9001 standard for what concerns quality, and involving an acoustician with a degree in building physics):
- study of different scenarios for the implementation of sound-absorbing linings (ceiling tiles and other suspended acoustic elements, e.g. on the underside of a roof, sound-absorbing wall coverings, dividers or screens) with acoustic simulation tools developed in-house (the prediction of the efficiency of the reverberation control of a room can be carried out with the SILDIS® simulation software) or based on sound ray tracing (requiring a digital model of the room)
- definition - in terms of acoustic quality (i.e. for what concerns the acoustic absorption coefficient or the equivalent absorption area), in quantity (as the case may be: number of units, density per m2, area) and in positioning - of materials (and soundproofing hardware) appropriate to improve a given situation
- evaluation of acoustic performance indicators e.g. reverberation time and when it makes sense, spatial sound decay, reduction in noise levels after the implementation of soundproofing components and systems (marketed or not by ITS)
- verification of the compliance of premises with objectives: regulatory, normative, or from particular technical specifications
ITS masters all aspects of the question of the effectiveness of the reverberation control of a room.
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[1] in France, according to the Order of August 30, 1990 taken for the application of article R. 235-11 of the labor code and relating to the reverberation control of work premises referred to in article R. 235-11 of the labor code:
- in buildings and rooms where machines and devices likely to expose workers to a daily sound exposure level greater than 85 dB(A) must be installed
- when it is established that the reverberation, evaluated by a predictive acoustics method, would cause an increase in the daily noise exposure level of a worker equal to or greater than 3 dB(A)