Impedance tubes are composed of tubes with a round or square cross-section. They have a loudspeaker at one end and the other end is closed with the test specimen and a reflective tube end. The specific impedance of a test object in the event of perpendicular incident sound can be determined in an impedance tube. This value is then used to calculate the reflection factor and the sound absorption coefficient.
Müller-BBM Industry Solutions GmbH has impedance tubes in accordance with ISO 10534 standard, with different sample dimensions and corresponding frequency ranges for testing the sound absorption coefficient and the reflection factor.
|Impedance tube no.||Sample dimensions||Frequency range|
|1||square, 600 mm x 600 mm||25 Hz...250 Hz|
|2||circular, diameter 100 mm||90 Hz...1.900 Hz|
|3||circular, diameter 30mm||500 Hz...6.300 Hz|
The transmission or sound reduction index R0 through a structural element with perpendicular incidence sound can also be measured with an impedance tube using an extended process.