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DESCRIPTION. Road surfaces with a void content higher than 10 Vol% (accessible cavities) significantly attenuate the sound radiation and sound propagation of tyre-road noise. The sound absorbing pro-perties of porous pavements or pavements with a high void content such as porous asphalt (PA), 2layer PA and noise-optimized thin lay-ers, are highly dependent on the installation conditions and the aging process. In our laboratory we can determine the sound absorption co-efficient of drill cores with an impedance tube.
PURPOSE. Determination of the sound absorption coefficient of test specimens in order to optimize road surface mixtures or to test real road surfaces.
MEASUREMENT METHOD. ISO 10534-2: Acoustics – De-termination of sound absorption coefficient and impedance in impe-dance tubes – Part 2: Transfer-function method.
SCOPE OF APPLICATION . Open porous samples or samples with a high void content, such as drill cores from roller compaction plates or from the top layers of PA, 2layer PA or noise-optimized thin pavement layers.
MEASUREMENT PROCEDURE. The test sample is mounted within the impedance tube. Then, a predefined acoustic signal is generated. The sound pressure inside the tube is measured at three microphone positions and the sound absorption coefficient can be calculated from the measurement results.
MEASUREMENT RESULTS. The final result is presented as the sound absorption coefficient at normal incidence for a frequency ran-ge between 50 Hz and 2 kHz, with a frequency resolution up to 2.7 Hz. In addition, the accessible void content of the sample can be deter-mined from the sound absorption coefficient.
MEASUREMENT CONDITIONS. The sample should be a cylinder with a diameter of 100 mm ± 2 mm. The sample must be dry. It may ha-ve a bottom dense layer.
DETERMINATION OF THE SOUND ABSORPTION COEFFICIENT (IMPEDANCE TUBE)
CONTACT.
Manuel Männel Phone: +49 (89) 85602-204
Mail: [email protected]
Thorsten Otto Phone: +49 (89) 85602-344
Mail: [email protected]
www.MuellerBBM.com
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