Measurement kit for acoustical complex properties testing
The determination of physical parameters of porous media has became of great significance for designing closed spaces by means of analytical and numerical predicting methods.
3Mics_MAA kit is based on the transfer matrix approach by using a three microphones technique; it allows the calculation the complex acoustical properties (characteristic impedance and complex wave number) in the frequency range between 50 Hz e 4300 Hz. Simultaneously, the kit permits the measurement of the surface properties (normal incidence surface impedance and sound absorption coefficient) according to ISO Standard 10534-2.
Parameters
- Characteristic Impedante, complex wave number, complex density, complex sound velocity;
- Surface impedance , Complex reflection coefficient, Normal incidence sound absorption coefficient;
- Transmission Loss for homogeneous materials.
Technical specifications
Tube diameter: 45mm.
Measurement chain:
- 3 (¼” ) microphones and preamplifiers;
- 4 channels signal conditioner;
- Power Amplifier for output signal;
- National Instruments device or Audio sound card. The sound card has to work in full duplex
- Software developed in Labview®.
Frequency range: 50-4300 Hz.
Excitation signal: Exponential sine sweep.
Post-processing procedures: Power and cross spectral density functions of impulse responses obtained by using convolution of exponential sine sweep.
A transfer function approach is used for determining acoustical parameters.
Applications
The use of complex acoustical properties is fundamental when it is necessary to model the sound propagation within porous media having arbitrary geometry. As an example it is possible to mention the modeling of porous media used in mufflers and silencers. In fact, according to the “equivalent dissipative fluid model” it is possible to use standard equations (i.e. Helmoltz eq.) with modified values of density and sound velocity, which are complex and frequency dependent. The same concept can be applied when it is necessary to model porous materials used in layered systems for automotive applications.
References
F. Pompoli, P. Bonfiglio, Tecniche avanzate di caratterizzazione fisico-acustica di materiali porosi, ATTI 35° Convegno AIA, Milano 11-13 Giugno 2008.
Download pdf
P. Bonfiglio, F. Pompoli, Comparison of different inversion techniques for determining physical parameters of porous media, Proceedings of ICA 2007, Madrid September 2-7 2007.
Download pdf
 |
