Revisiting Airflow Resistivity Measurement of Fibrous Porous Materials via Impedance and Transmission Loss Tubes in the Mid-Frequency Region

Abstract Airflow Resistivity (AFR) is one of the most significant parameters of any given fibrous porous material to predict the corresponding acoustical performance. In this experimental research, the AFR is first measured via the ISO 9053 method and then the results are compared with indirect measurements via an impedance tube (IT) and a transmission loss (TL) tube following ASTM-E1050 and ASTM-E2166, respectively. The said indirect measurements are carried out till duct cut-off frequencies, i.e., 100 Hz to 4500 Hz to demonstrate that AFR can be evaluated within an error of <±2.5% even in the mid-frequency (~1-2 kHz) region superseding the limits of ultra-low frequency (2-100 Hz) region as mentioned in the previous literatures. From the present experimental studies, it is also revealed that the AFR calculated via impedance tube measurement is comparatively ambiguous since there are periodic peaks and valleys due to the resonance of the air cavity used in the measurement. In contrast, the AFR calculated via the transmission loss tube is even, particularly in the mid-frequency (~1-2 kHz) regime making it more prudent and reliable for AFR estimations. &#xD;