Beitrag zur Problematik der Diffusitat des Schallfeldes im Hallraum
The present work deals with the influence of the diffuseness of the sound field in a reverberation chamber on the sound absorption coefficient.
A diffuse sound field was obtained with the help of cylindrical scatterers suspended in the reverberation room. It is shown that for reverberation chambers of a size as recommended by the ISO it is better to use a larger number of smaller elements. However, the scattering elements should be large enough to be already effective at the limiting frequency of the reverberation room. The scattering objects must be distributed equally over the room with arbitrary orientation relative to each other and to the walls.
Measurements were made in two reverberation rooms supplied with scattering elements. The measured sound absorption coefficients differed by not more than 10%.
Furthermore the relation of Meyer and Kuttruff for the limiting frequency of reverberation rooms derived from measurements with model reverberation chambers, was confirmed for rooms of a size as recommended by the ISO. It was found that rotating loudspeakers with reflector plates did not improve the diffuseness of the sound field or the conditions of measurement.
Increased diffuseness reduces the scatter of the measured values of reverberation time especially at low frequencies. This is explained by the increased attenuation of the natural frequencies of the rooms.
Oblique walls produce a more even distribution of the natural frequencies whose number is the same as in a comparable room with parallel walls. The obliquity of the walls also results in a reduction in the variation of measured sound pressure with position of the microphone. A further reduction in this variation is achieved in both reverberation chambers by the suspended scattering elements.
A diffuse sound field was obtained with the help of cylindrical scatterers suspended in the reverberation room. It is shown that for reverberation chambers of a size as recommended by the ISO it is better to use a larger number of smaller elements. However, the scattering elements should be large enough to be already effective at the limiting frequency of the reverberation room. The scattering objects must be distributed equally over the room with arbitrary orientation relative to each other and to the walls.
Measurements were made in two reverberation rooms supplied with scattering elements. The measured sound absorption coefficients differed by not more than 10%.
Furthermore the relation of Meyer and Kuttruff for the limiting frequency of reverberation rooms derived from measurements with model reverberation chambers, was confirmed for rooms of a size as recommended by the ISO. It was found that rotating loudspeakers with reflector plates did not improve the diffuseness of the sound field or the conditions of measurement.
Increased diffuseness reduces the scatter of the measured values of reverberation time especially at low frequencies. This is explained by the increased attenuation of the natural frequencies of the rooms.
Oblique walls produce a more even distribution of the natural frequencies whose number is the same as in a comparable room with parallel walls. The obliquity of the walls also results in a reduction in the variation of measured sound pressure with position of the microphone. A further reduction in this variation is achieved in both reverberation chambers by the suspended scattering elements.
Document Type: Research Article
Publication date: 01 January 1960
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