Example: Acoustics in Coupled Rooms

1. Example:Acoustics in Coupled Rooms

2. Acoustics in Coupled Rooms Introduction • The sound transmission across a building element sample is simulated. • The setup is similar to the one stipulated by the ISO 15186/3 standard as implemented at the Icelandic Building Research Institute (IBRI) in Reykjavik. • This example shows how Extended Multiphysics can be used to split a model into separate exchangeable modules. • In particular, a 2D model of the sample is inserted into the 3D test bench.

3. Acoustics in Coupled Rooms – Problem Definition Geometry Sending room • In the 3D geometry, the rooms are modeled as much further apart than they really are. • The rooms are connected via the sample plate, which is modeled in a separate 2D geometry. Receiving room Sound source Sample plate

4. Acoustics in Coupled Rooms – Problem Definition Domain Equations – Acoustics • Frequency domain acoustics is goverened by a slightly modified Helmholtz’s equation for the acoustic pressure, p. • Material properties are density, r0, and speed of sound, c. • Note that the density cannot be eliminated from the equation unless it is a global constant

5. Acoustics in Coupled Rooms – Problem Definition Domain Equations – Structure • As a simple example, a 1 cm thick, homogenous steel plate is used as sample. • The plate is modeled using plate elements of Reissner-Mindlin type. • The pressure difference between the rooms enter the plate equations as a surface load.

6. Acoustics in Coupled Rooms – Problem Definition Boundary Conditions – Acoustics • The natural boundary condition corresponds to inward normal acceleration. Three types are used: Specified normal acceleration, given by plate movement Specified impedance, partly absorbing Hard wall

7. Acoustics in Coupled Rooms – Problem Definition Boundary Conditions – Structure • The plate is mounted in the opening between the rooms using wooden spacers and wedges. • Where the plate is in contact with the spacers, it is considered free to rotate, but not to move. • The rest of the gap between plate and niche wall is filled with a soft sound absorbing material that does not restrict the plate’s movements.

8. Acoustics in Coupled Rooms – Results Results • The instantaneous pressure pattern is shown as isosurfaces. • The wall color represents the sound pressure level in the two rooms (in dB).

9. Acoustics in Coupled Rooms – Results Results • The sound reduction index is not a smooth function of frequency. • This is probably due to the absence of damping in the source room and the sample plate causing pronounced resonance effects.