With the Microflown acoustic absorption set-up it is now possible to measure the acoustic properties of materials, in situ and real time. The acoustic properties of materials such a reflection coefficient, absorption coefficient and transmission coefficient are of importance to engineers. In comparisson with other techniques as for example the kundts tube a sample can be measured under normal conditions of use such as in a car interior, this in normal and oblique angels in a broad banded frequency range. This becomes possible due to the direct measurement of the both quantities needed, sound pressure and particle velocity, with the unique PU probes of Microflown Technologies. Restrictions to samples like traditional methods are with technique less of influence. Such as restrictions on sample size is almost a  negligible factor in this method. Also the application bandwidth on the types of material is very broad, inhomogenieus materials and soft porous materials can all be tested with the set-up.

The 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.

List of equipment

 

• Surface Impedance software
• Grid with elastics fastened and spherical loudspeaker mounted.
• Specified probe (PU mini and/or PU match) with mounting screw(s).
• Handle
• Mini tripod to mount under the handle
• Lemo probe cable
• Jack loudspeaker cable
• Signal conditioner
• Loudspeaker amplifier
• Sound card
• Cables signal conditioner to sound card
• USB sound card cable to computer
• 110/230 Volt to 18Volt adaptor
• Adaptor cable
• Gooseneck probe mounting

The complete set-up comes in a protective pelicase.

        

More info

• Background information can be found in Chapter 6: 'Impedance' of the Ebook
• Scientific papers on the subject of acoustic absorption
• Presentation on acoustic absorption can be found at the presentations page
• Video about "acoustic absorption" measurements can be found at the video page

Key papers

• Non destructive and in situ acoustic testing of inhomogeneous materials
  Tijs et al., ERF 33, Kazan, Russia, 2007
• An ultra miniature measurement tool to measure the reflection coefficient of acoustic damping materials in situ
  de Bree et al., SAE, 2007
• Two complementary Microflown based methods to determine the reflection coefficient in situ,
  de Bree et al., ISMA 2006
• Measuring the free field acoustic impedance and absorption coefficient of sound absorbing materials with a combined particle velocity-pressure sensor
  R.Lanoye et al., JASA May 2006
• A practical device to determine the reflection coefficient of acoustic materials
  R. Lanoye et al., ISMA 2004 Leuven, Belgium
• Broad band method to determine the normal and oblique reflection coefficient of acoustic materials
  Hans-Elias de Bree, Reinhilde Lanoye,  Simon de Cock, Jos van Heck, SAE 2005