Wich acoustic performance levels and criteria for offices and associated areas or for other tertiary buildings excluding school premises?
The question of acoustic performance levels and criteria for offices and associated spaces or for other tertiary buildings is crucial with respect to premises for which acoustic comfort is a major qualitative aspect.
In France, the standard NF S31-080 (January 2006) Acoustics - Offices and associated areas - Acoustic performance levels and criteria by type of area addresses the following areas: individual office, collective office, open space, meeting room, relaxation area, restaurant, circulation, tray to accomodate.
Depending on the case, the reverberation time or spatial decay are the basic technical requirement.
For each type of room, the standard defines and classifies the acoustic environment in three performance levels:
- "current" level is what is required by regulation, and in the absence of legal texts, the minimum functional level which does not ensure acoustic comfort.
- "powerful" level is acoustic performance beyond the level of "current". This level provides an acoustic comfort conducive to good working conditions.
- "very Powerful" level corresponds to maximum acoustic performance made possible by action on all different elements of the buiding construction (design, architecture, materials, ....). This level aims at the perception of useful noise and at non-perception of unnecessary noise: so there is a qualitative notion suitable for the purpose and activity to be conducted in the premise.
In addition, NF HQE Tertiary Buildings certification distinguishes buildings of which acoustic performances reflect best current practices. This certification covers the phases of planning, design and construction for new buildings and renovations.
The acoustic criterion of a space and its interactions with neighboring spaces is quantified through two concepts: the sensitivity of the space and the aggressiveness of the space.
The sensitivity of the space relies to the acoustic environment expected by the occupants. The more sensitive the space is, the more hearing emergences (from adjacent spaces or from space itself) are troublesome.
One thus distinguish:
- very sensitive areas, such as: individual offices, rest areas, infirmary, customers private spaces (hotels), etc.
- sensitive areas, such as: open spaces, empty space awaiting conversion, meeting rooms, dining rooms, lounges, entrance halls, sports area (hotel), etc.
- not much sensitive areas such as: halls, waste premise, restrooms, corridors, some sales areas, common areas dedicated to customers traffic (trade), bathing areas (hotel), warehouse (Logistics), etc.
The aggressiveness of the space quantifies the impact of the space on the neighboring space. The more aggressive the space is, the greater the average sound level of the space is and the more the space impacts on neighboring areas. We thus distinguish:
- highly aggressive areas such as: dining areas, auditorium, delivery areas, common areas dedicated to customer traffic, sales areas, bar, disco, games rooms, bathing areas (hotels), warehouse (logistics), etc.
- aggressive areas such as: open spaces, meeting rooms, sales areas, rooms (hotel) etc.
- the non-aggressive areas such as: individual office, rest areas, infirmary, customers private spaces, reading rooms (or quiet lounges), library (hotel), etc.
Thus, by combining the notion of sensitivity with the notion of aggression, we can classify the different spaces found in buildings in categories according to the sector (office, education, retail, hospitality, logistics).
In terms of generic requirements, the concern referred to as "base level" aims at accounting the location of sensitive and very sensitive spaces with respect to aggressive and very aggressive spaces for inner and outer disturbances while the concern referred to as "performance level" and the concern referred to as "high performance level" aim at optimizing the shape and volume of spaces in which the internal acoustics is an issue.
Depending on the case, the reverberation time or the spatial decay are the basic technical requirement, when this is not the equivalent absorption area.
ITS masters all aspects of the question of acoustic performance levels and criteria for buildings, e.g. offices. (new or renovation):
- technical specification
- on-site verification (measurements by a technician qualified in physical measurements, specialized in instrumental techniques using duly calibrated and verified sound level meters)
- recommendation and advice
- marketing of materials and works
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Wich efficiency for the reverberation control of a room ?
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  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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 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)
Why choose baffles made of melamine foam, rather than any other suspended baffle?
Such a choice is appropriate in all cases where it is looked for a baffle with both a very good absorption factor, a minimum mass, a minimum cost and minimum installation costs according to different possible techniques allowing all architectural aspects.
Verifying the performance of acoustic baffles made from melamine foam can be conducted in accordance with ISO 354 Acoustics - Measurement of sound absorption in a reverberation room
Which metallic wall panels for the reverberation control of a room?
As far as metallic wall panels for the reverberation control of a room are concerned (also known as acoustic insulation panels) such as those used for current applications in the field of industrial soundproofing or in premises of tertiary buildings, like reducting the reverberation of a room or increasing the spatial sound decay in a room, they generally consist of an absorbent filling (quite often: mineral wool) covered by a surfacing (mostly: a fiber glass) and also by a perforated protection (mostly: galvanized or painted steel).
Sound absorption of metallic wall panels for the reverberation control of a room
Sound absorption, which is obviously a fundamental characteristic of metal wall panels for the reverberation control of premises, depends on the characteristics of each of the layers present: filling, surfacing and perforated protection.
As required, the perforations of the protection of panels for reverberation control of a room can generally be circular (perforated plate) or in the form of slots (absorbent panels with metal blades).
Perforations (from left to right) circular (orthogonal or hexagonal arrangement), square or slotted perforations taken into account with the software SILDIS® for the sizing of room reverberation control panels
When the characteristic dimension of the holes and the perforation rate are large enough, the influence of the perforated protection is negligible i.e. the acoustic absorption coefficient of the rear layer (eventually: multiple) is almost unchanged, at the very least with regard to the frequency range whose 1/1 octave center frequencies are between 125 Hz and 4 kHz, as is commonly considered in the construction industry.
Otherwise, the coexistence of the holes of a perforated protection and a backing porous medium e.g. mineral (rock, glass) or polyester wool, foam (even: air) constitutes a resonator whose acoustic behavior is distinguished by the more or less selective character of the absorption of sounds wich is resulting (with regard to what the - multiple - choice of combinations of all kinds of dimensional parameters and of the airflow resistance of the rear porous medium makes it possible to modulate the performance with regard to the variation of the sound absorption coefficient depending on frequency).
In order to increase the absorption coefficient in a given frequency range, an intermediate plate (usually made of steel) and also a additional absorbent spacing layer may be inserted into the metallic wall panels, the performance of such absorbent panels then being (partially) based on the effect of resonant membrane (also known as resonator).
Such panels are then so efficient that they can then be used for acoustic measurement and testing rooms, e.g. anechoic rooms, aeroacoustic wind tunnels.
As for many other applications of multilayer structures involving mineral e.g. rock, glass or polyester wool, foams, plates e.g. steel, aluminum, metal, plaster - perforated or not -, the prediction of acoustic performance of metallic wall panels can be performed with the simulation software SILDIS®.
The verification of acoustic performance of metallic wall panels can be made in accordance with ISO 354 Acoustics - Measurement of sound absorption in a reverberation room.
Other technical characteristics of metallic wall panels for the reverberation control of a room
A powder coating usually provides the best possible protection against corrosion: up to classification C5 according to ISO 12944 whereas providing a visual aspect appropriate for the context.
In some cases, the frame of metallic wall panels (metallic absorbing panels) can be made of stainless steel (SS 304, SS 316) or of aluminum.
As required, the absorbing lining may consist of acoustic foam or of polyester wool and for some applications, protected by a waterproof surfacing (polyurethane film and for extreme cases: painting).
When required, metal wall panels for reverberation control can be matched with dividers, when these hardware are combined as part of the same soundproofing project (e.g. in shared offices, in the form of open spaces).
Whatever the reasons, metal panels are not always the preferred solution for the reverberation control of a room, in which case different alternatives can be proposed, with equivalent performance in terms of sound absorption, but sometimes with an aspect better harmonized with some visual atmospheres taking into account architectural preferences or particular furniture (e.g. for premises welcoming young children, for some dining rooms, meeting rooms, training rooms):
- panels with perforated protection in plaster (gypsum) or wood
- panels without perforated protection i.e. with a fabric surfacing
ITS masters all aspects of the question of the choice of metal wall panels for the reverberation control of a room.
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What are the input data useful for reducing the reverberation of a room?
The reduction of the reverberation of a room (due to the reflections of sound waves on the walls which delimit it and also on objects of different nature) is required in many contexts:
- spaces with young children
- classrooms and training facilities of educational establishments
- music rooms (with or without amplified music broadcast)
- sports halls and gymnasiums
- catering areas (e.g. canteens)
- work premises (e.g. workshops, open space offices, meeting rooms)
Depending on the case, the reduction of the reverberation of a room can be envisaged in the perspective of:
- improving speaking and listening comfort
- increasing confidentiality and discretion
- limiting of ambient noise levels e.g. with regard to the prevention of hearing risks
The input data useful for reducing the reverberation of a room are mainly:
- a physical indicator of the existing acoustic situation i.e. the exiting reverberation time 
- the use of the premise 
- the level of acoustic performance wich is required (desired reverberation time, desired sound pressure level, desired spatial sound decay) 
- the surfaces available for the implementation of absorbent materials (area of available surfaces, acceptability of overweight for wall supports or for roofs)
In very numerous cases, the reaction to fire of considered materials is also taken into account as well as considerations of appearance (architectural style, colors, materials ...).
In the case of realization in the food industry, in pharmaceuticals, or in hospitals, specific constraints related to hygiene are involved and may necessitate the use of particular absorbing coatings (with waterproof washable cover) or the use of stainless steels.
Other parameters may be involved such as the authorized mass, the required longevity or the available budget.
In the particular case of industrial premises, the location of noisy equipment (machines, production lines), their sound emission spectrum and the location of workstations (which one wishes to protect) constitute additional useful data in the framework of a project for which the objective is a reduction of the reverberated noise (resulting from the reflection of acoustic waves during their mean free path between the point of emission and the point of reception).
All of the useful input data for reducing the reverberation of a room can be used (as at ITS: by an acoustician qualified in building physics):
- for predictive acoustic calculations (in some cases: with numerical simulations based on sound ray tracing involving a 3D modeling of the considered space)
- for the selection or development of construction systemshaving appropriate acoustic characteristics (i.e. an acoustic absorption coefficient often as close as possible of 100 % in the frequency range of interest)
- for the prediction of values possible to be obtained, after works, for the reverberation time and when it makes sense, for the spatial sound decay, for the reduction of noise levels; of course the evaluation by ITS of these acoustic indicators before works is also possible
Soundproofing materials and corresponding installation works can also be marketed: ITS masters all aspects of the question of useful input data for reducing the reverberation of a room.
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 limit values of maximum reverberation duration (reverberation time) or of minimum equivalent absorption area must be taken into account for certain premises in tertiary buildings, minimum values of spatial sound decay are to be considered for work spaces