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Home  Applications
Acoustic absorption |
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| Acoustic absorption Measurements |
User benefits
Click here for more infoThe procedure to determine the acoustic absorption in situ is to apply a point source loudspeaker to generate noise towards the acoustic sample, measure the spherical impedance, calculate the spherical reflection coefficient and convert the spherical reflection coefficient to a planar reflection coefficient. In situ / no Kundts tube The acoustic properties of materials such a reflection coefficient, absorption coefficient and transmission coefficient are of importance to engineers. Traditionally, Kundts tube methods are used to determine the reflection and absorption coefficients. The method requires a sample to be taken and put into the tube. Only the normal angle of sound wave incidence can be determined. With a PU probe, capturing both sound pressure and acoustic particle velocity simultaneously in one spot, the acoustic surface impedance can be determined without taking a sample. It thus allows measurements under circumstances that were not possible until then, e.g. measuring acoustic impedance of walls for the purpose of room acoustics. Normal and oblique angles A method to determine also the acoustic material properties under oblique angles of sound wave incidence was developed by Tamura. The method requires an anechoic room, 10 square meters of sample size and 4 hours measurement time. The reflection coefficient can directly be calculated from the acoustic surface impedance. And the acoustic surface impedance can directly be measured with a pu probe. In a peer reviewed JASA paper by KU Leuven and University of Oldenburg it was proven that a PU based method shows comparable results to method developed by Tamura. However, sample size is only a few square decimeters and the measurement time only a few minutes. No anechoic room is required. Broad banded The same JASA paper demonstrated that broad banded results can be obtained. Other methods are frequency band limited. No anechoic room In a peer reviewed paper presented during the SAE 2007 Microflown Technologies it was proven that this PU method also works outside of an anechoic room. It allows a large group of users to measure the acoustic properties of materials themselves right on the spot. Fast Where other methods require hours of work to get results yhe PU method provides results for each angle of sound wave incidence in a few minutes. Reproducible The theoretical accuracy of methods is often hampered by a lack of reproducible results, because of different types of Kundts tube used and improper preparation of samples causing acoustic leakages. The PU acoustic absorption method is not susceptible to these method related flaws. Real time The actual measurement time is extremely short providing instantaneous results. Small sample size The spatial resolution of the PU acoustic absorption method is relatively high, allowing small samples to be tested, e.g. an ISO A4 / US letter format. End of line control In industry, there is a trend towards 100% testing and narrowing the range of specifications. The PU acoustic absorption method allows fast, reproducible, real time and in situ measurements, all stepping stones for end on line control. Adaptive systems The compactness of the sensor set up and real time measurements are stepping stones for adaptive systems to be developed, e.g. to adjust noise attenuating properties of materials and systems. More info
Key papers
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