Measurement Techniques


Any sound field is described by two complementary acoustic properties, the scalar value 'sound pressure' and the vector value 'particle velocity'. The Microflown in-situ technique to determine impedance, absorption and reflection makes use of a Microflown particle velocity sensor and a sound pressure microphone. Both sensors are mounted in the PU-mini probe that is positioned close to the material with a sound source positioned at a certain distance.  The sound pressure and acoustic particle velocity are measured right at the surface of the material. The impedance can be derived from the ratio of sound pressure and particle velocity. From this, the material reflection and absorption can be calculated. The probe is able to measure in the whole audible range but the lower frequency limit of the method at this moment is 300Hz. This is due to the low sound pressure emission from the loudspeaker at low frequencies (and the limited dimensions of the sample). The current usable bandwidth for the method is 300Hz - 10kHz. The method makes it possible to measure under different angles, measuring with a high spatial resolution of just few millimeters, measure all type of materials and material sizes. There is also no need to take destructive samples and measurement can be performed when the materials are installed.