Principle of impedance tube
In the impedance tube a plain sound wave is generated and sent against a sound absorbing specimen in front of a reverberant termination. The resulting sound pressure is measured by using two microphones in front of the material sample. The sound absorption coefficient of the material is determined by evaluating the incoming and reflected sound energy.
Specimen holder I
- Application: determination of sound absorption coefficient of materials in the laboratory according to DIN EN ISO 10534-2
- Specimens: cylindrical specimens with a diameter of 15 mm, 30 mm, 40 mm or 100 mm
- Method: prepared cylindrical specimens of variable thickness are mounted and sealed into the specimen holder, which can be continuously positioned and adjusted
Specimen holder II
- Application: determination of sound absorption coefficient in situ according to DIN ISO 13472-2 (sound absorption coefficient < 0,15)
- Specimens: road surfaces and plates of specimens with a dimension of at least 300 mm x 300 mm
- Method: adapter for tight attachment of impedance tube to the surface of the specimen
The measurement system AFD 1000 is supported by the analysis software AFD 1001.
- determination of material properties as a function of frequency
- averaging of results of various material samples
- simple management and comparability of results by application of database
An extension of the impedance tube to the transmission tube (AFD 1200 + analysis software AFD 1201) allows the determination of the sound insulation, the transmission coefficient, the complex impedance and the complex wave number.
By applying the transfer matrix method according to Song and Bolton, the insertion loss of mufflers (see software for acoustic design of mufflers AFD 8001 – AcoustiCalc®) and the diffuse sound absorption coefficient (comparison to measurements in the reverberation chamber according to DIN EN ISO 354) can be predicted directly.
Compression specimen holder impedance tube
As of now, a novel compression specimen holder extends the application range of the impedance tube, transmission tube and the airflow resistivity meter AFD 300 – AcoustiFlow®.
The specimen holder can be adjusted in length nearly continuously and allows the defined compression of cylindrical specimens and fills to measure the sound absorption coefficient, transmission loss, absorber values and the airflow resistance. Also, thin fabrics as well as multilayer systems can be installed with control.
- Type I (Standard)
- Inner diameter: 40 mm
- Frequency range: 100 Hz – 4.400 Hz
- Type II
- Inner diameter: 100 mm
- Frequency range: 50 Hz – 2.000 Hz
- Type III
- Inner diameter: 30 mm
- Frequency range: 150 Hz – 6.600 Hz
- Type IV
- Inner diameter: 15 mm
- Frequency range: 150 Hz – 10.200 Hz
- Thickness of specimen
- AFD 1000: 260 mm
- AFD 1200: 80 mm
- Compression specimen holder: 170 mm
- Type: 1/4″, BNC (female), class 1
- Frequency range: 20 Hz – 20 kHz
- 2/4 simultaneously sampled analog input channels, BNC, IEPE-conditioning
- compatible to MATLAB* and LabVIEW**
* MATLAB is a registered trademark of The Math Works, Inc.
** LabVIEW is a registered trademark of the National Instruments Corporation