2444, rue Bonin Sherbrooke, J1K 1C4, Canada

(819) 346-5666 info@mecanum.com

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).

Main advantages of the product

Measurement method in accordance with the ASTM and ISO standards;

User-friendly interface;

Measurement method from the scientific literature;

Superior manufacturing quality.

Other Mecanum’s Related Products

Grids and rings Porous material slicer Circular cutter Resistive screen and fabric holder
Enviro Weather station Anechoic Termination FOAM-X Digital Piston NOVA

More Information

➡ Download Flyer

➡ Information and Price