Building Acoustics

Sound absorbers 195

incidence plane wave having a sound pressure of 1 Pa. We observe that the displacement
has a pronounced maximum in the same frequency range as found for the absorption
curve.

0 500 1000 1500 2000 2500 3000

Frequency (Hz)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

A

bsorption factor Measured (L1)

Measured (L2)

FEM

Analytical

Figure 5.30 Normal incidence absorption factor of 50 mm polyurethane with hard backing. Measurement data,
using a two-microphone free field technique and two loudspeaker positions (L1, L2), are compared both with
analytical results and results using a finite element method (FEM). From Vigran et al. (1997).

0 500 1000 1500 2000 2500 3000

Frequency (Hz)

0.0E+000

5.0E-005

1.0E-004

1.5E-004

2.0E-004

Displacement (mm/Pa)

Figure 5.31 Calculated displacement at the surface of 50 mm thick polyurethane foam. Incident sound pressure
equal 1 Pa.