Abstract
Efficient ultrasonic noise reduction by using enclosures requires the
knowledge of absorbing properties of materials in the frequency range
above 4 kHz. However, standardized methods enable determination of
absorption coefficients of materials in the frequency range up to 4 kHz.
For this reason, it is proposed to carry out measurements of the sound
absorption properties of materials in the free field by means of a
tone-burst technique in the frequency range from 4 kHz to 40 kHz at angles
of incidence varying from 0° to 60°. The absorption coefficient of a
material is calculated from the reflection coefficient obtained by
reflecting a tone-burst from both a perfectly reflecting panel and a
combination of this panel and the sample of the tested material. The tests
results show that mineral wool and polyurethane open-cell foam possess
very good absorbing properties in this frequency range.
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