A university acoustics research group was developing novel porous acoustic absorber composites as part of a research programme investigating materials for architectural noise control and hearing conservation equipment. The research required systematic characterisation of the normal incidence sound absorption coefficient and specific acoustic impedance of material samples at various thicknesses, densities, and surface treatments across a wide frequency range.
The group's existing measurement capability was limited to high frequencies above 1 kHz. To fully characterise their materials, including the low-frequency absorption performance that is critical for practical noise control applications, they needed measurement capability extending down to 50 Hz. The PLACID dual-tube impedance tube system provided this extended range in a compact laboratory instrument.
The research group successfully published multiple papers using data from the PLACID impedance tube system, with measurement uncertainty documented in the papers' uncertainty sections. The system has been in continuous operation for 3 years at the time of writing, with annual recalibration maintaining measurement validity.