Acoustic Impedance and Transmission Loss Measurement of Materials

Acoustic materials are often judged in complex spaces where reflections, mounting conditions and background noise make the result difficult to interpret. An impedance tube gives the lab a controlled normal-incidence sound field, so materials can be compared under repeatable conditions.

For R&D teams, this is useful because a foam, liner, fabric, perforated panel or enclosure layer can be tested before it is installed inside a vehicle, duct, room or machine guard.

In an absorption test, microphones mounted along the tube measure the sound pressure field before the sample. From the transfer function between microphone positions, the software estimates reflection behavior, absorption coefficient and impedance-related quantities.

This tells the engineer how much incident sound energy is absorbed by the sample at each frequency. The result is more useful than a single rating because material behavior often changes sharply across low, mid and high bands.

Transmission loss testing evaluates how much sound passes through a sample. The tube arrangement measures the pressure field on the incident and transmitted sides, then calculates the loss across frequency.

In practical terms, this tells the engineer how much sound energy is blocked versus how much gets through the material system. (Note: this is a different quantity from structural "transmissibility", the dimensionless ratio of transmitted to input vibration used in isolation-mount work — transmission loss is an airborne-sound quantity expressed in dB.) Low transmission is desirable for barriers, covers, partitions and enclosure panels; controlled data helps compare candidate material stacks.

The T-Sonus kit supports 100 mm, 30 mm and 16 mm tube options to cover 50 Hz to 10 kHz across the tube set. Precision 1/4 inch microphones feed a four-channel acquisition system, while TSONUS software handles channel setup, calibration, SNR checks, phase calibration, measurement, averaging and reporting.

The workflow supports ISO 10534-2, ASTM E1050 and ASTM E2611 style testing, with 2, 3 or 4 microphone methods depending on the measurement. For documentation, the software can merge results from multiple frequency ranges, smooth the combined curve and export reports for comparison or submission.