The input data useful for the simulation of the dissipation (absorption) of an acoustic structure are mainly the type of fluid, its thermodynamic state (pressure, temperature, density), and also - of course - intrinsic characteristics of each layer.

In a concrete and exhaustive way, the evaluation of the dissipation of an acoustic structure (absorbing sound - either as panel or lining for walls or roof in a room or as filling in a noise reduction device that a silencer is -) requires knowledge of the following input data (listed in the order of their input for a calculation with the SILDIS® software Module 2 / 2+ Prediction of acoustic performance of plane partitions and walls :

  • temperature
  • pressure
  • (in case of the presence of a porous medium):
    • (as a minimum) resistivity, porosity, (and, if known) tortuosity, thermal and viscous characteristic lengths (or else designation of the nature - e.g. rock, glass, basalt, polyester, ceramic wool or foam to be precised -, trade name and density)
    • thickness
  • (in the event of the presence of a surfacing, if it is not modeled as a porous medium):
    • superficial air flow resistance
    • weight per unit area
    • thickness
  • (in the event of the presence of a perforated protection, if it is not modeled as a porous medium):
    • designation of the geometry of the holes (e.g. circular, square, slot-shaped perforation) and their arrangement (e.g. square, hexagonal, staggered)
    • diameter or side of holes / width of slots
    • center distance (for slots only)
    • perforation rate
    • thickness
    • (optionnal) mass density, the consideration of this parameter allowing, in some contexts, to improve the accuracy of prediction

In the event that it is not clean dry air, the additional following input data (for gas at silencer operating conditions) would be required:

  • individual constant
  • adiabatic constant
  • density
  • speed of sound
  • dynamic viscosity
  • specific heat at constant pressure
  • thermal conductivity

This is the list of useful input data to simulate the dissipation / sound absorption of an acoustic structure in linear regime. In the nonlinear regime, the characteristics of the acoustic excitation (nature, sound pressure levels per frequency band) must also be considered.