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 for predicting 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 transmission loss (TL) tube following ASTM E1050 and ASTM E2611, respectively. The indirect measurements are carried out up to the duct cut-off frequencies, i.e. 300–4500 Hz, to demonstrate that AFR can be evaluated within an error of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mtext>⩽</mml:mtext> </mml:mrow> </mml:math> 2.5% even in the mid-frequency ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>∼</mml:mo> </mml:mrow> </mml:math> 1–2 kHz) region, superseding the limits of the ultra-low-frequency (2–100 Hz) region as mentioned in the previous literature. From the present experimental studies, it is also revealed that the AFR calculated via IT measurement is somewhat 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 TL tube is even, particularly in the mid-frequency ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>∼</mml:mo> </mml:mrow> </mml:math> 1–2 kHz) regime, making it more reliable for AFR estimations.