Sound absorption in an impedance tube

Measuring sound absorption in the impedance tube offers manufacturers and users of absorber materials the opportunity to test their products under standardized conditions. Besides the absorption coefficient, impedance is also measured in order to obtain detailed information about the material. Since only small-sized samples are needed, this method is particularly suitable for developing and optimizing new materials. In addition, fully-developed products can be certified in accordance with DIN EN ISO 10534-2.

The impedance tube consists of three main elements: a long tube into which the material sample is inserted at one end, a loudspeaker at the other end, which generates a standing wave in the tube using a noise signal, and two microphones, which are located at a distance from each other as well as from the sample and the loudspeaker. Impedance is calculated on the basis of the known original signal from the loudspeaker, the positions of the microphones and the signals from the microphones which have been modified due to absorption by the sample. The absorption coefficient of the material can be determined from this.

Thanks to the impedance tube, also known as Kundt's tube, detailed absorber measurements can be carried out under normal incidence. These are essential when certifying and controlling the quality of absorber materials. At Fraunhofer IBP in Stuttgart, we have different sizes of impedance tube available (diameter: 30 mm (250 Hz to 6500 Hz) and 100 mm (100 Hz to 1850 Hz) as well as square ones: 200 mm (100 Hz to 2500 Hz), 250 mm (80 Hz to 1000 Hz), thus allowing materials to be tested and the frequency range and absorption coefficient to be determined for both very small and larger specimens.

Would you like to learn more about the possibilities of measuring sound absorption in the impedance tube or receive advice on material testing in accordance with DIN EN ISO 10534-2? Our scientists look forward to hearing from you!