Which means for limiting the spread of noise?

The question of means of limiting the spread (propagation) of noise (in relation to various issues) is important for anyone concerned with the acoustic comfort of buildings, the protection of workers or the preservation of the environment.

What means of limiting the spread (propagation) of noise are used specifically inside buildings ?

There is, basically, only one category of means of limiting the spread (propagation) of noise used specifically inside buildings:

that having to do with reverberation control: it comes to the implementation of absorbent materials (according to the possibilities: in the form of a wall lining, and/or in the form of a suspended ceiling or suspended baffles or/and in the form of a floor covering) which make it possible to increase spatial sound decay and therefore, for example, in work premises, to limit the propagation of noise from machines or production lines towards distant workstations (and, what is not nothing: with limiting the amplification of sound levels due to the effects of reverberation, which can also be important in technical rooms). The main characteristic sought is sound absorption (the sound absorption coefficient, which varies according to the frequency, is expressed in %); the performance, in terms of limiting the spread (propagation) of noise, increases with this indicator (provided that a sufficient proportion of the total surface of the walls of a room is treated, and that the distribution of the absorbing surfaces is fairly homogeneous ). In an anechoic room (used for R&D work in acoustics, in industry as well as in universities or engineering schools), the goal is to overcome the physical limits constituted by the walls of a room. tests or a laboratory.

What means of limiting the spread (propagation) of noise are used indifferently inside or outside buildings?

The means of limiting the spread (propagation) of noise used indifferently inside or outside buildings can be classified into different categories:

• those that have to do with acoustic insulation: it is a question of opposing the propagation of sounds by the implementation of acoustic structures such as elements of the envelope of buildings or constructions inside buildings (consisting of fully enveloping structures: enclosures for noisy equipment, acoustic cabins ^{[1] [2] [3]}) e.g. floors, roofs, walls and partitions - which may include doors and windows -. For constructions (housing, tertiary premises, industrial building) the airborne noise insulation illustrates the limitation of the propagation of noise from noisy spaces to the spaces to be protected (interior or exterior). The main characteristic sought is the sound reduction (the sound reduction index, variable depnding to the frequency, is expressed in dB); performance, in terms of noise propagation limitation, increases with this indicator
• those that have to do with the sound barrier effect: these are constructions (noise barriers walls) that oppose the propagation of noise at specified locations. The main characteristics sought are sound reduction and sound absorption as mentioned above; the on-site performance depends on the positioning, with respect to the device for limiting the spread of noise, of the sound source and the location that one wishes to protect, the difference in the path of the sound waves path  induced by the presence of the noise-cancelling wall (e.g. depending on its height, if it is unlimited in length) and the properties, in terms of sound absorption, of the adjacent surfaces (e.g. the suspended ceiling of an open space, the under-roof of a industrial building)
• those that have to do with limiting the transmission of structure-borne noise. The main characteristic sought is vibration filtering (the vibration filtering rate, variable according to the frequency, is expressed in %); performance, in terms of noise propagation limitation, increases with this indicator. Decoupling devices (springs when it comes to obtaining low frequency performance e.g. when considering a concept like the "box in the box" type, studs and elastomer supports are useful for the anti-vibration suspension of equipment in technical rooms, boiler rooms as well as for the separation of pipes and ducts)
• those having to do with noise reduction for aeraulic networks or facilities with pressurized fluids e.g. for openings or vents. The main characteristic sought is the insertion loss (variable according to the frequency, expressed in dB) inseparable from the aeraulic performance (i.e. the total pressure loss) which must not reduce the efficiency of the facility. Silencers are devices for limiting the spred of noise with very variable design, shape, dimensions and construction depending on the context (there are big differences between a silencer in a Heating Ventilation Air Conditioning - HVAC - network, involving low-flow air with near-atmospheric thermodynamic conditions and a gas turbine exhaust muffler involving combustion gas with very high-temperature, high-velocity)

What does ITS offer with regard to means of limiting the spread (propagation) of noise ?

What ITS offers with respect to the means of limiting noise spred (propagation) (depending on the context):

• audit and advice: on-site sound measurements for diagnosis, acoustic simulations, impact study, sizing calculations for soundproofing equipment
• marketing of all means of limiting the spread (propagation) of noise: for acoustic insulation (products and constructive systems for all types of construction - building and industry -), for the implementation of acoustic screens (anti-noise walls in all cases, soundproof screens for catering rooms and collective offices), anti-vibration devices, silencers of all kinds (all these materials: developed and built with a view to sustainable performance)

Spread the word !

^[1] the cabins for musicians allow the practice of a musical instrument while being freed from the surrounding noise, and without disturbing the neighbors (a certain degree of anechoicity is required inside)
^[2] in some workplaces, booths are specially designed constructions to protect people (e.g. machine operators) from ambient noise
^[3] audiometric booths are constructions specially designed to allow examinations and tests related to hearing

Which means for reducing noise at source?

Noise reduction at source consists in reducing the sound power of a noisy hardware or equipment, by means such as an enclosure (acoustic hood) for a machine, a soundprrofing partition for a noisy area in a workshop for example, a silencer for a ventilation opening (or an suction / outlet / exhausy linked to an industrial process).

Reduction of noise at source by means of sound-absorbing enclosures or partitions

Reducing noise at source by means of soundproofing enclosures or partitions consists in implementing a continuous separation between two spaces:

• the one that contains the noise source (even when there is only one machine or one piece of equipment, the noise source is not always unique - when different organs have significant noise emissions -)
• the one one wants to protect from noise

In practice, noise reduction at source can take quite different forms, in relation to the size that needs to be considered:

• canopies, soundproof casings for small or medium-sized sound sources e.g. pumps, fan housings, small motors (thermal or electric), compressors of limited capacity
• enclosures for machines of all kinds (wood and metal working, cardboard manufacturing, processing of raw materials for the construction sector)
• partitions (between floor and roof e.g.connecting with two opposite walls of a building) for large noisy machines and facilities (e.g. printing presses)
• soundproof containers and buildings for high-power heat engines, high-capacity compressors, combustion turbines

In many cases (in the industrial sector) the noise reduction at source by means of enclosures or sound-absorbing partitions can be achieved using metal constructions:

• with a frame/a framework
• with multilayer acoustic insulation panels having properties both in terms of sound reduction (i.e. opposing the transmission of noise) and in terms of sound absorption (i.e. preventing the sound level amplification invloved - otherwise - by the presence of an obstacle to the propagation of noise in a free field); they can advantageously be modular and removable (to allow maintenance operations)
• with acoustic doorsets to allow access (for people - on foot or motorized - or for equipment)
• with sound-reducing glass frames to allow visibility from a space separated by the device for noise reduction at the source to the other
• with noise reduction equipment for ventilation openings which are often necessary

Reduction of noise at source by means of silencers

Reducing noise at source by means of silencers is required in different contexts:

• when the considered fluid is air with a temperature and a pressure close to atmospheric conditions for the ventilation of soundproof enclosures or partitions, for applications - in constructions - related to Heating, Ventilation, Air Conditioning (HVAC)
• for industrial processes involving air condensers (dozens of fans are sometimes to be considered for a single installation), cooling towers (the diameter of the fans can exceed 10 meters), air intakes for engines and turbomachines (the entrance area may exceed 100 square meters)
• when the considered fluid is a combustion gas (i.e. with a very high temperature - which can reach 850°C in the case of special processes, generally between 500°C and 650°C when it comes to thermal engine exhausts or gas turbines -)
• when the considered fluid is an industrial gas possibly very cold (if it is expanded) or very hot (if it is a vaport steam vent)

The operating principle (dissipative i.e. involving a sound-absorbing material, or reactive i.e. with sound reflections induced by the geometry of the internal parts), the design (acoustics, aeraulics), the construction (choice of steels, resistance to pressure) must be studied on a case-by-case basis and can lead to devices that vary greatly in size, shape and performance.

What ITS offers in terms of noise reduction at source

What ITS offers in terms of noise reduction at source (depending on the case):

• an on-site diagnosis with sonometric measurements
• an engineering mission for the research and development of solutions (such design office work may require calculations of sound propagation and impact and sizing in terms of acoustics and aeraulics)
• noise reduction hardware:
  • components: silencing materials, industrial soundproofing panels and acoustical claddings, silencers of all kinds
  • systems: soundproof canopies, sound enclosures, complete noise attenuating buildings

Spread the word !

What is the difference between sound insulation and reverberation control?

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.

Spread the word !

^[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)

What is soundproofing ?

Soundproofing involves the implementation of means of protection of workers against noise, and/or of environmental protection against noise, and/or of means for compliance with regulatory in terms of acoustics of buildings (industrial, tertiary, residential ...). Soundproofing can involve different techniques:

• for reverberation control (of a room)
• for acoustic insulation
• for the implementation of noise barriers
• for teh implementation of silencers

What does soundproofing based on reverberation control consist in ?

Soundproofing based on reverberation control consists in limiting the reflections of sound waves on surfaces, often hard, (e.g. the limits of an enclosed space), founding the phenomenon of reverberation. It is therefore a question of covering such surfaces with materials having properties in terms of acoustic absorption (up to 100%) in a frequency range of interest. The main effects of soundproofing based on acoustic correction are:

an increase in the temporal sound decay, quantified by the time - alias the duration - of reverberation (in general: expressed in seconds) which is all the shorter as the soundproofing solution implemented is effective

an increase in spatial sound decay, quantified by the rate of spatial sound decay (generally: expressed in dB(A) per doubling of the distance to the source) which is all the higher as the soundproofing solution implemented work is effective; 6 dB(A) per doubling distance corresponds to a free sound field (as observed outdoors or in an anechoic room)

What dies soundproofing based on acoustic insulation consist in ?

Soundproofing based on acoustic insulation consists of limiting the transmission of sound from one space to another (e.g. from the inside of a building to the outside - or in the opposite direction -, from one premise to another premise - from a room to another room if it comes to a dwelling - or even from a technical room to a living room or to a hospital or hotel room). It is therefore a question of interposing an acoustic structure (often: multilayer) having acoustic attenuation properties (scale in dB without upper limit) in a frequency range of interest (in the building sector: corresponding to the bands of 1/1 octave centered on 125 Hz to 4 kHz).

With regard to acoustic insulation between interior and exterior (of a building, or of a construction similar to it), and with regard to constructions inside a building (e.g. soundproof cabins), the main components of acoustic insulation are walls and partitions (if necessary with doors, windows), roofs, floors. With regard to the acoustic insulation of machines and equipment, of pipe networks, the main components are the walls of casings and cowlings, lagging of the thermal insulation type with materials having properties in terms of noise transmission limitation.

The main effects of soundproofing based on acoustic insulation are:

• a difference in sound pressure level between the two spaces separated by the construction erected with a view to providing acoustic insulation

What does soundproofing based on the implementation of acoustic screens consist in ?

Soundproofing based on the implementation of acoustic screens consists in limiting the propagation of noise (inside a building or outside) by means of constructions (also called: anti-noise walls) having not the continuity of those provided for acoustic insulation: at the very least, an acoustic screen has an upper edge, at the level of which the phenomenon of diffraction of the acoustic waves takes place (in practice, the acoustic screens are not infinite, and this phenomenon concerns often several vertical edges or a single vertical edge - it happens that a screen is installed perpendicular to a wall -, unless it is a construction forming an enclosure without discontinuity (e.g. of rectangular shape, with 4 walls surrounding an air condenser). Acoustic screens must combine the sound absorption and sound reduction functionalities mentioned above in a frequency range of interest (which rarely includes the low frequencies, due to inherent low performance). Regarding the implementation of an acoustic screen:

• the efficiency is characterized by the insertion loss (i.e. the difference in sound pressure levels measurable at a specified location on the one hand with the screen and on the other hand without the screen), unless it is is a sound level at a measurement point

What does soundproofing based on the implementation of silencers consist in ?

Soundproofing based on the implementation of silencers relates to constructions intended to limit the propagation of noise from openings or vents without opposing the passage of a fluid. This concept therefore covers very different operating realities, depending on whether it is air in quasi-ambient conditions (e.g. ventilation, air conditioning) or an industrial fluid (not only a combustion gas), possibly pressurized and/or with an extreme temperature (very low during expansion, or very high in the case of exhaust gases or steam purges). A silencer can be dissipative, i.e. with a sound absorbing lining e.g. with fibrous materials including mineral wool of all kinds and foams - with surfacing - or having to do with the presence of discontinuities causing reflections of sound waves e.g. changes in duct sections, connections between chambers, tube perforations, change in the direction of fluid circulation; these two principles are often combined e.g. for combustion engine exhaust silencers, for pressurized gas venting silencers.

Regarding the implementation of an acoustic screen:

• the efficiency is characterized by the insertion loss (i.e. the difference in sound pressure levels measurable at a specified location on the one hand with the silencer and on the other hand without the silencer), unless it is is a sound level at a measurement point

ITS markets all products and services for soundproofing

ITS markets all products and services for soundproofing (construction, industry):

• components: acoustic panels and building envelope elements of all kinds, silencers for all applications
• systems: for the reverberation control of premises, for the acoustic insulation of buildings, acoustic screens and noise barriers
• acoustical engineering e.g. on-site measurements, solution studies, calculations, sizing

Spread the word !

Where to begin a process to fight against noise?

It is appropriate to begin a process of struggle against noise by taking the advice of professionals of soundproofing, such as Isolation Technologie Services, able to accompany a Client throughout his process of sound nuisance reduction by providing to him the expertise (of its human resource) of more than 25 years in the field of acoustics in all sectors of activity: industry, environment, energy, testing rooms, building.

Depending on the context, the noise control approach proposed by ITS may include:

• a diagnosis, including - on site - sound level measurements (and in some cases, reverberation time measurements and/or spatial sound decay measurements inside buildings):
  • such acoustic metrology is then carried out by a workforce qualified in physical measurements (specialized in instrumental techniques) with sound equipment duly calibrated and verified
  • comparison with reference values ​​(e.g. from regulations, standards, technical specifications), identification and prioritization of noise sources are often an integral part of such missions
• a study of solutions; the selection or development of constructive systems for noise reduction often requires simulations (e.g. sound propagation and impact) and sizing calculations with specific software (some decision-making tools being developed by human resources of ITS)
• the marketing of soundproofing materials (for applications inside buildings or outside)
  • materials, products and components: panels and linings with properties in terms of sound absorption and/or attenuation, silencers of all kinds
  • systems i.e. constructions, possibly turnkey (on-site installation then being part of the scope): reverberation control of premises, soundproofing casings and enclosures for machines, noise barriers, soundproof buildings

In the field of noise control, experience counts when it comes to offering solutions adapted to each context (taking into account all the related issues), with proven effectiveness and at an affordable price. 

Plan, do, check, act: these are the key words to characterize a noise control approach as offered by ITS since all our products and services are subject to ISO 9001 certification for the management of our quality system.

Spread the word !