Model Tests for the Determination of the Sound Absorption Coefficient in the Reverberation Chamber

Difficulties arising with the determination of the sound absorption coefficient in the reverberation chamber are examined in the present paper for two model reverberation chambers (right parallelepiped, 2.16 m³, sphere, 0.524 m³) at the third octave with a centre frequency of 10 kHz, Sillan being the test material. With the aid of a newly developed arrangement the reverberation time could be read by an electronic counter directly during the measurement. It was investigated how the absorption coefficient depends on the measures taken for scattering the sound and on the area of the absorbing material without the edge effect. Curved plates suspended in the room and hemispheres of 12 cm diameter attached to the walls were used as scattering bodies. Investigations were made with a combination of these as well as with only one kind at a time.

It was discovered that the cause of difficulties with the measurement of the sound absorption coefficient in the reverberation chamber has to be located mainly in the lack of diffusion of the sound field. In addition the edge effect must be taken in account.