Prediction of noise emissions from buildings and other constructions with Module 10 of the acoustic calculation software SILDIS^®

The prediction of sound emissions from buildings and other constructions with Module 10 of the acoustic calculation software SILDIS^® is useful when the distance at which one wishes to calculate the sound pressure level (resulting from noise transmission through walls and/or from the propagation of sounds emitted by noisy hardware installed outside, e.g. leaning against a wall or placed on a roof) is not small enough, when compared to the size of the sound sources, for them to be considered as punctual and then allow simple formulations to be used for the determination of spatial sound decay.

Calculations with Module 10 of software are thus possible for extended noise sources (i.e. with a significant area or line-shaped) almost without any limitation for their dimensions.

Practical cases are thus the assessment of the sound impact of various structures :

• buildings and premises separating two spaces (one: interior and the other: exterior) of all kinds e.g. industrial buildings and enclosures for the limitation of noise from large equipment (e.g. in the energy production sector : high-capacity compressors and other turbomachines, engines whose power is counted in megawatts - MW -)
• gas turbines inlet and exhaust ducts (the section can reach or exceed 100 m2 with lengths of a few tens of meters)
• coverings of noisy machines and production equipment

Basis of the prediction of noise emissions from buildings and other constructions with Module 10 of the acoustic calculation software SILDIS^®

The prediction of noise emissions from buildings and other constructions with Module 10 of the acoustic calculation software SILDIS^® is based on the consideration of a partition (wall or roof) of rectangular shape, to which is assigned :

• a macro-directivity in the direction of the receiver (i.e. of the location specified for the calculation of the sound pressure level)

The prediction of noise emissions from buildings and other constructions with Module 10 of the acoustic calculation software SILDIS^® is based on the consideration of indoor conditions (in considered premise) :

• the sound pressure level at 1 or 2 m from the partition
• the (quantified) quality of the diffusion of the acoustic field
• the characteristic impedance of the fluid in question (air, except in the case of exhaust gas)

A low a decrease as a function of distance is considered.

The prediction of noise emissions from buildings and other constructions with Module 10 of the acoustic calculation software SILDIS^® uses a mesh of surfaces, distinguishing between :

• the envelope, characterized by a sound reduction index, the input data being measurement results (e.g. in the laboratory) ^[1] or simulation with another module of the SILDIS^® software ^[2]
• openings i.e. surfaces which are of a different nature from the envelope, characterized by :
  
  • a specific sound power level, which is combined with that due to the sound field inside the room e.g. to simulate the presence of fans in ventilation facilities
  • a sound reduction index, the input data being the results of measurements (e.g. in the laboratory) ^{[1] [3]} or simulation with other modules of the SILDIS^® software ^{[2] [4]}
  • a directivity index
  • a low a decrease as a function of distance

Concretely, the openings can be used to simulate the presence of doors, windows (or other glazed surfaces) or apertures (e.g. in the case of soundproof enclosures of machines: cutouts for passages of raw material supplies or supply and evacuation devices such as inlets or outlets for parts - for the above, the self-noise is then generally irrelevant, except for example in the case of noisy electric motors of treadmills or conveyors -) or ventilation openings communicating with the inside of the room, possibly equipped - as in the case of paint booths, technical rooms, machinery halls and enclosures for noisy equipment - with fans (their own noise is then rarely negligible).

As a software display, a diagram illustrates the positioning of the openings taken into account in the context of a simulation (according to the input data entered ; cf. fig. 1

Figure 1: screenshot of a display of the SILDIS® Module 10 software - diagram illustrating the positioning of openings taken into account in the context of a simulation [5] ; from left to right: a baffle silencer (with a front section of 16.8 m2) with fans and an industrial door (with an area of 22.4 m2) in the facade of an industrial building 40 m long and 12.5 m high

• external noise sources that are not affected by the sound reduction of the envelope or openings, characterized by :
  
  • a sound power level
  • a directivity index
  • a low a decrease as a function of distance

In concrete terms, external noise sources can be used to simulate the presence of equipment whose impact in terms of acoustics it is desired to take into account - whether they are installed in front of a façade or on a roofing - just like that of the upstream (air intake) or downstream (discharge) end of aeraulic networks whose sound emissions are independent of the noise level in the room; they are therefore useful with regard to - for example - air condensers or other Heating Ventilation Air Conditioning - HVAC - equipment.

As a software display, a diagram illustrates the positioning of an external sound source taken into account in the context of a simulation (according to the input data entered) ; cf. fig. 2.

Figure 2: screenshot of a display of the SILDIS® Module 10 software - diagram illustrating the positioning of an external sound source taken into account in the context of a simulation [5] ; on the left: a set of air condensers (with an area of 9.6 m2) on the facade of an industrial building 40 m long and 12.5 m high

The prediction of noise emissions from buildings and other constructions with Module 10 of the acoustic calculation software SILDIS^® includes the modeling of the propagation of noise between the elementary surfaces of the mesh and the receiver (i.e. the location specified for the calculation of the level sound pressure level), with consideration :

• of different models of spatial sound decay (depending on the hypothesis made regarding the radiation of elementary sound sources)
• of a solid angle factor, and possibly taking into account separately sound waves reflections at ground level
• of atmospheric sound attenuation, the input data possibly being simulation results with another module of the SILDIS^® software ^[6]

Results of the prediction of noise emissions from buildings and other constructions with Module 10 of the acoustic calculation software SILDIS^®

The prediction of noise emissions from buildings and other constructions with Module 10 of the acoustic calculation software SILDIS^® makes it possible to obtain different output data :

• the total sound power level (combining envelope, openings and external noise sources) :
  
  • by 1/1 octave frequency band of central frequencies between 31 Hz and 8 kHz, and in overall A-weighted level (as software output data for the sound power level, a noise map according to a rather similar concept to that illustrated - for the sound pressure level - by figure 3 is also available); the sound power level can be compared (using the software) with a reference value, with a clarification of the improvement needed to meet a sepcified objective
• the resulting sound pressure level at a specified location :
  
  • by 1/1 octave frequency band of central frequencies between 31 Hz and 8 kHz, and in overall A-weighted level
  • in the form of a noise map of the partition (e.g. in terms of deviation from the average of the sound pressure level at the receiver due to each of the meshes modeling the wall) ; cf. fig. 3.

Figure 3: screenshot of a display of the SILDIS® Module 10 software - noise map (deviation from the average of the sound pressure level at the receiver due to each of the meshes modeling the wall) within the framework of a simulation [5] ; for openings as depicted in Fig. 1 and external noise source as depicted in Fig. 2

• the resulting sound pressure level at a specified location, contextualized by taking into account, possibly (depending on additional input data) :
  
  • the impact of other sources of noise (e.g. other sides of the same construction)
  • the amplification due to sound reflections at the receiver (e.g. due to the presence of large sound-reflecting surfaces such as facades of other buildings)
  • the background noise

The sound pressure level can be compared (with the software) with a reference value, with a clarification of the improvement needed to meet a specified objective.

About the prediction of noise emissions from buildings and other constructions with Module 10 of the acoustic calculation software SILDIS^®

The prediction of noise emissions from buildings and other constructions can be carried out with Module 10 of the acoustic calculation software SILDIS^®:

• by technicians and engineers from design offices, even without in-depth knowledge of acoustic modeling techniques: the implementation of the functionalities has been carried out to promote ease of use (not only for acousticians and acoustic consultants) and the speed of obtaining results with a computer (including: a laptop) even basic, with a self-service (with subscription) in ASP mode ^[7] ; alternatively: by the human resources of ITS (which has developed and which markets this calculation means) - engineering and software publishing in the field of acoustical insulation are activities of ITS regularly assessed in accordance with the requirements of the ISO 9001 standard -
• in the context of studying the impact, in terms of acoustics, of various facilities in the building sector (technical rooms, enclosures for machinery and HVAC equipment) or industry (all projects relating to enclosures e.g. containers, canopies and soundproof buildings - made of masonry, with metal or wooden constructions - whatever the size) with a view to protecting the environment. It is thus possible, within the context of a soundproofing project, to optimize the acoustic performance of the various sub-assemblies constituting a partition of a building or of another construction (depending on the case: solid elements - including insulation panels of all kinds - doors and windows, openings with or without noise reduction devices that silencers are) and to make the best choices: not only for the construction systems of the considered structure but also for the noisy hardware possibly installed outdoors (by determining the efficiency - in terms of insertion loss - required for equipment to reduce their noise emissions which may be prove necessary to comply with a given noise limit)
• for calculations :
  
  • only requiring input data without any particular difficulty for their collection (when it comes to standardized acoustic characteristics of building systems and noisy equipment), without iteration and using a single computer file
  • with results being reliable for all configurations, precise, with respect to which it is easy to take into account modifications of modeling scenarios for the development of optimized soundproofing solutions, with noise maps of the studied partition of a building or of another construction analyzed, and with performance indicators that can be used directly for analyzes of compliance with regulatory, normative constraints, or resulting from technical specifications

From an academic point of view, the above applies :

• to enclosures, i.e. to spaces entirely enclosed by a structure, each of the faces of which (walls, roof) can then be subject, in turn, to as many separate sound impact calculations
• with, as far as the propagation of noise radiated by the partitions is concerned, free acoustic field conditions (possibly on a more or less reflective plane, but without obstacles or finite limit)

In practice, it is possible to extend the field of use of the software :

• to anti-noise screens and barrier walls, i.e. constructions without a roof, if the conditions are met for the effects of the diffraction phenomenon to be negligible (e.g. distance from the receiver to the considered partition sufficiently low, screen of sufficiently large dimensions)
• to structures located inside a room, if the conditions are met for the effects of the reverberation phenomenon to be negligible (e.g. distance from the receiver to the considered partition sufficiently low, influence of the reverberated component of the acoustic field in the room sufficiently weak)

The Module 10 of the SILDIS^® acoustic calculation software is an essential and irreplaceable tool for anyone concerned with the sound emissions of buildings and other constructions.

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^[1] NF EN ISO 140-3 Acoustics - Measurement of sound insulation in buildings and of building elements - Part 3: Laboratory measurements of airborne sound insulation of building elements
^[2] cf. link SILDIS^® Module 2 prediction of acoustic performance of plane partitions
^[3] ISO 7235 Acoustics ISO 7235:2003 Acoustics — Laboratory measurement procedures for ducted silencers and air-terminal units — Insertion loss, flow noise and total pressure loss
^[4] cf. link SILDIS^® Module 1 prediction of acoustic and aeraulic (aerodynamic) performance of silencers
^[5] cf. link User’s manual for the software SILDIS^® section 10 example 10.4.1 industrial building wall
^[6] SILDIS^® Module 8B prediction of atmospheric sound absorption
^[7] ASP = Application Service Provider