Sound insulation and reverberation control contribute to noise limitation and sound comfort in buildings, however with very different means of action (which can sometimes be combined).
Sound insulation
The sound insulation is the set of processes implemented for getting a determined noise reduction, i.e. limiting the transmission of sound from one space where noise is generated toward another that one wishes to protect. Depending on the context, one or other of these spaces can be a room or premises in a building (home, hotel, healthcare or leisure establishment, workplace) or outside (depending on the direction of sound transmission that one want to prevent); in some cases, the two spaces between which acoustic insulation must be considered are inside buildings.
Sound insulation thus requires the implementation of a continuous envelope (with the fewest possible weaknesses, being undesirable paths for sound waves) made with variable elements according to the construction technology considered in a given context:
- masonry (solid or hollow blocks, bricks, concrete)
- plaster-based constructions (plaster blocks, gypsumboards)
- wooden constructions (with natural or reconstituted wood)
- metal constructions (most often: steel, sometimes: aluminum)
- glass constructions (e.g. glazing and bay windows, door portholes, roof windows)
With a view to obtaining a high performance in terms of sound insulation (the sound reduction index - expressed in dB depending on the frequency, or in overall value, sometimes weighted - is the intrinsic characteristic of the elements, the performance being all the greater as this indicator is high),most of the walls and partitions, roofs, floors must be airtight; however, openings are often necessary, for the sanitary renewal of air in premises or for the evacuation of heat dissipated by hardware: this then require the use of silencers, which reduce the propagation of noise whereas not opposing not (too much) to the passage of a fluid (which is often air, but which can in some cases be a combustion gas).
In France, sound insulation is regulated for different buildings:
- constructions being covered by the Order of June 30, 1999 relating to their acoustic characteristics
- constructions being covered by the decrees of April 25, 2003 relating to the limitation of noise: educational establishments, hotels, health establishments
Limiting noise at work (production workshops, offices) makes acoustic insulation work necessary in many contexts (to satisfy regulatory constraints or to comply with normative specifications relating to the reduction of worker exposure to noise, or the acoustic comfort of workspaces - not only in industrial sector -):
- acoustic casings and machine enclosures
- soundproofing laggings of duct and pipe networks
- constructions of soundproof offices (including: cabins) for staff
The efficiency of insulation can be quantified on site (using a sound level meter) depending on the issues:
- by measuring the difference between the sound pressure levels between two spaces (in dB)
- by measuring the sound pressure levelin one of the spaces, at a specified location (in dB ref. 20 μPa), eventually before and after works
Reverberation control
Reverberation control consists in the implemention of absorbing materials in a premise in order to limit its reverberation time (the persistance of sound after a noise source has been shut off), and/or to increase its spatial sound decay, i.e. to improve the inner acoustics inside a premise by limiting the amplification of sound levels due to the phenomenon of reverberation.
Reverberation control thus requires the implementation (with as homogeneous a spatial distribution as possible, the ground only rarely offering possibilities of action, in practice) of elements in forms which may vary according to the context (and whose some can sometimes be combined):
- mineral wool
- polyester wool
- foams
- perforated panels (e.g. wood or metal)
- membranes (i.e. resonators for low frequency sound absorption)
With a view to obtaining high performance in terms of acoustic correction (the acoustic absorption coefficient - expressed as a % depending on the frequency, or as an overall value, sometimes weighted - is the intrinsic characteristic of the elements, the performance being greater than this indicator is high), a sufficient proportion of the available surfaces (variable according to the sound absorption coefficient of the elements and according to the volume of the room) must be covered.
In France, acoustic correction is regulated for different buildings:
- the constructions being covered by the decrees of April 25, 2003 relating to the limitation of noise: educational establishments, hotels, health establishments
- working premises [1]
Noise limitation makes reverberation control works necessary in many contexts (e.g. to comply with normative specifications relating to the acoustic comfort of the spaces concerned):
- workplaces such as offices e.g. when they are shared - this is the case of open spaces -, meeting and training rooms
- rooms for speaking and listening (including for music)
- sports halls (e.g. gymnasiums, swimming pools)
- dining rooms
The effectiveness of reverberation control can be quantified on site (using a sound level meter) according to the issues:
- by measuring the reverberation time (in s)
- by measuring the decrease in sound level by doubling the distance to the source (in dB)
- by measuring the difference between the sound pressure levels before and after works (in dB)
Combination of sound insulation and of reverberation control
The combination of sound insulation and sound correction is often useful:
- to limit sound transmissions from a enclosed space, because the existence of limits to the space which contains the noise source (a fortiori when there are several of them) induces (compared to the free acoustic field) an amplification of the sound levels which increases (all other things being equal) the noise level in the space (indoor or outdoor) where the noisy emissions are received; are thus concerned the walls of machine cowlings and noisy equipment enclosures (which, depending on their size, sometimes resemble buildings, e.g. in the case of combustion turbines) and also test benches enveloppe
- to limit the sound level in a space for which a low background noise is sought (e.g. for a quiet room, even more for an anechoic room) because the existence of limits to such a space induces (compared to the free acoustic field) an amplification of ambient sound levels
- in the case of cabins for musicians, or music rehearsal rooms (acoustic: soft or loud, or amplified music), when it is a question both of offering internal conditions favorable to the practice of an instrument or of several, and to prevent noise disturbance for the neighbors (sometimes also: so that the musicians can free themselves from noise outside the volume in which they practice their art)
It follows from the above that the combination of acoustic insulation and reverberation control requires the use of acoustic structures (often: multi-layered), with intrinsic properties:
- in terms of sound reduction
- in terms of sound absorption
Soundproofing panels (e.g. for industrial applications, but not only) - such as those marketed by ITS - meet these two requirements.
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[1] if they are likely to expose workers to a daily noise exposure level greater than 85 dB (A) and when it is established that the reverberation, assessed 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)