Rectangular ducts and circular ducts are the basis for many products and construction systems for applications related to soundproofing: dissipative silencers, resonant silencers, etc ... . They also form the connection pieces which are often implemented on the occasion of the installation of silencers in ventilation systems for example.
The sound attenuation of the walls of such ducts must be taken into account for the design of equipments for which noise transmission through the envelope they are (for soundproofing equipments) or through connecting ducts of the latest must be limited ; in some cases (depending on the acoustic objectives being sought), single-leaf constructions are sufficient, while in other cases a double-leaf construction is required: it can then take the form of an external lagging (like for thermal insulation) of the duct casing.
ITS has integrated the computation of the acoustic performance of rectangular ducts and of circular ducts walls to the simulation software SILDIS® (this is the subject of Module 3).
Calculation routines have been implemented for the calculation of the transmission loss of those equipments (for circular ducts: either spiral wound or not. Of course, the mechanical characteristics  of the material considered are input data for the simulation, but the installation conditions (in the case of a monolithic wall, the concept of infinite plate is not applicable due to the existence of connections in the angles if it is a duct of rectangular - or square - cross section and other specificities in terms of vibro-acoustics should be considered in the case of cylindrical ducts) must be taken into account (just like the flow rate of a transported fluid, in some cases).
Following the modification operationsof the software SILDIS®, the comparison of simulation results with bibliographic data (results of measurements, results of calculations by others ...) has shown a satisfactory agreement with regard to the transmission of noise through ducts with varied geometries, constitutions and dimensions.
The expected result of improvements to the acoustics calculation software SILDIS® (due to the integration of the computation of the acoustic performance of rectangular ducts and of circular ducts walls) is an improvement of the accuracy of the sizing of soundproofing equipments such as ventilation silencers and in general: of all industrial silencers (and of their connecting parts) which design is very demanding given the sound power levels of the considered noise sources (before soundproofing) and expected performance in terms of sound insulation in the context of protection of workers, or of preservation of environment, or of improvement of the acoustic comfort in buildings.
Computer Aided Design (CAD): SILDIS® calculation software for acoustics and aeraulics in the construction sector (in Excel format)
 Young's Modulus, density, Poisson's factor, loss coefficient