Comparison of Bulk Property Measurement Methods Using Impedance Tube

Two measurement methods of calculating the bulk properties of porous materials, Utsuno's 2 cavity method based on ISO-10534-2 and ASTM E1050 standards using a 2 microphone impedance tube and Song's transfer matrix method (ASTM E2611 standard method) using 4 microphone transmission loss tube, are compared. Utsuno's method is a method to determine the bulk property from two specific impedances which are measured using different air cavities behind the sample. This method has two issues; one is that divergence of the bulk properties due to the division-by-zero, while the second issue is that observed bulk properties vary widely in the low-frequency range. On the other hand, Song's method to determine bulk properties is conducted by measuring the sound pressure in the tube which allows you to calculate the sound pressure and particle velocity on both the front and back faces of the specimen, which can be used to derive many material characteristics. The One-load and Two-load measurement techniques can be used in this method. When using the two-load method, the divergence phenomena of the bulk properties are not observed and variations in low-frequency range are small compared with Utsuno's method.