2444, rue Bonin Sherbrooke, J1K 1C4, Canada

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Impedance and Transmission Tube Using 3 Microphones


Mecanum’s 3 microphones impedance and transmission tubes are specifically designed to measure the main normal indicators of a wide range of acoustical materials. The method is based on ASTM E1050 and ISO 10534-2 standards for the absorption coefficient (α), the reflection coefficient (R) and the surface impedance (Zs). All other indicators are determined using the 3 microphones technique12  which uses equations of ASTM E2611. The 3 microphones technique is an improvement of the ASTM E2611 where unknown termination loads are replaced by known cavities. The third microphone is inserted in the piston and always exposed to a maximum pressure for a better signal to noise ratio.


**  Large spacing between µ1 and µ2 is essential for better results at low frequencies (as stated in ASTM E1050)

*** µ3 is built in the termination


Material properties

➡ Normal incidence sound absorption coefficient (α)

➡ Normal incidence complex reflection coefficient (R)

➡ Normal surface impedance (Zs/Zair)

➡ Normal incidence sound transmission loss (TL)

➡ Characteristic impedance (Z/Zair)

➡ Wave number (k)

➡ Transfer matrix coefficients (Tij)

➡ Equivalent/effective dynamic density (ρeq)

➡ Equivalent/effective dynamic bulk modulus or compressibility (Keq)


Tube Internal Diameter Frequency Range
29 mm  200-6600 Hz
44.44 mm 100-4300 Hz
 100 mm 35-1900 Hz


TUBE-X is a user-friendly software that will simplify the measurement procedure. It’s also fully compatible with FOAM-X software that can extract non-acoustic parameters of porous materials using the inverse method with a 2 microphones absorption measurement and the indirect method using the 3 microphones measurement.


  • Every Mecanum impedance tube is supplied with grids (for samples with low mechanical strength) and rings (to avoid leaks).

Other Mecanum’s Related Products

➡ Grids and rings

 Verification and calibration samples

 Porous material slicer

 Circular cutter

 Resistive screen and fabric holder

 Enviro Weather station

 Three-microphone version upgrade



More Information

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