The PLACID impedance tube system is a complete laboratory instrument for measuring the normal incidence sound absorption coefficient and specific acoustic impedance of acoustic materials using the two-microphone transfer function method. The system complies with ISO 10534-2 and ASTM E1050-12 and provides calibrated, traceable measurements across the frequency range of each tube configuration.
The impedance tube is the standard instrument for material acoustic characterisation in research, product development, and quality assurance. It provides complete frequency-dependent absorption and impedance data from a small, easily prepared sample — rather than the large samples, specialised rooms, and complex logistics required for reverberation room measurement. For most material characterisation work in the 50 Hz to 6.3 kHz range, the impedance tube is the practical first choice.
The PLACID impedance tube system is calibrated as a complete assembly: the microphone sensitivities are determined in the installed positions within the tube, and the loudspeaker transfer function is characterised at the measurement frequencies. The calibration package includes ISO/IEC 17025 accredited sensitivity certificates for both measurement microphone positions and a system verification record confirming that the transfer function H12 meets the residual background condition of ISO 10534-2 Annex A. This complete system calibration ensures that results are directly traceable to national measurement standards without the need for separate position-by-position corrections during measurement.