Principle
Principle of Impedance Tube (Kundt’s Tube)
In the impedance tube a plane 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.
Extension of Impedance Tube
An extension of the impedance tube to the transmission tube (AED 1200 + analysis software AED 1401) allows the determination of the characteristic absorber values (wave number and characteristic impedance), the transmission coefficient and the sound insulation (transmission loss) by applying the Two-Load Method with 4 microphones according to ASTM E2611 (Transmission Matrix Method). On such basis, the insertion loss of mufflers (see software for acoustic design of mufflers AED 8001 – AcoustiCalc® Silencer) and the diffuse sound absorption coefficient (see software for acoustic design of sound absorbers AED 3001 – AcoustiCalc® Absorber, comparison to measurements in the reverberation chamber according to DIN EN ISO 354, especially rated sound absorption coefficient of the material according to DIN EN ISO 11654) can be computed directly (see overview measuring systems vs. analysis software).
Extension of measuring system AcoustiTube® to AED 1200 (Type I to III)
Extension to transmission tube with terminating cap and support for microphone for application of Two-Load Method with 3 microphones
Compression specimen holder for measurement of sound absorption coefficient, characteristic absorber values and transmission coefficient of compressed materials, fills, fabrics and multi-layer systems
Specimen Holders
Type of Specimen Holders
Type I
- Application: determination of sound absorption coefficient of materials in the laboratory according to DIN EN ISO 10534-2 and ASTM E1050
- 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
Type 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
Compression Specimen Holder
As of now, a novel compression specimen holder extends the application range of the impedance tube, transmission tube and the airflow resistivity meter AcoustiFlow®
The specimen holder can be adjusted nearly continuously and allows the defined compression of cylindrical specimens and fills to measure the sound absorption coefficient, characteristic absorber values, transmission loss and the airflow resistance. Also, thin fabrics as well as multi-layer systems can be installed with control.
Software
The measurement system AcoustiTube® is supported by the analysis software AcoustiStudio – Module Sound Absorption.
- Determination of material properties as a function of frequency
- Averaging of results of various material samples, frequency ranges and impedance tubes
- Simple management and comparability of results by application of database
The analysis software AcoustiStudio allows the application of impedance tubes of arbitrary geometry.
Analysis software AcoustiStudio – Module Sound Absorption
Analysis software AcoustiStudio – Module Sound Transmission
Software impedance tube for measurement of sound absorptions coefficient
