Measuring sound absorption properties of porous materials using a calibrated volume velocity source

Abstract

Measurement of acoustic properties of sound-absorbing materials has been the source of much investigation that has produced practical measuring methods. In particular, the measurement of the normal incidence sound absorption coefficient is commonly done using a well-known configuration of a tube carrying a plane wave. The sound-absorbing coefficient is calculated from the surface impedance measured on a sample of material. Therefore, a direct measurement of the impedance requires knowing the ratio between the sound pressure and the volume velocity. However, the measurement of volume velocity is not straightforward in practice and many methods have been proposed including complex transducers, laser vibrometry, accelerometers and calibrated volume velocity sources. In this paper, a device to directly measure the acoustic impedance of a sample of sound-absorbing material is presented. The device uses an internal microphone in a small cavity sealed by a loudspeaker and a second microphone mounted in front of this source. The calibration process of the device and the limitations of the method are also discussed and measurement examples are presented. The accuracy of the device was assessed by direct comparison with the standardized method. The proposed measurement method was tested successfully with various types of commercial acoustic porous materials.

An electroacoustic method for measuring airflow resistivity of porous sound-absorbing materials

“…It can be seen that we need the values of M AC and C AT . To obtain these values, we may perform a calibration consisting of two steps: 1) a measurement of the electric impedance without the upper volume V up with the original backing volume V dw and 2) a second measurement of electric impedance after adding a known upper volume V [25]. In the first case, we measure a resonance frequency f 0 given by…”

Eco-Materials with Noise Reduction Properties

“…This method has been standardized by ISO 10534-2 [21]. At low frequencies, large tubes may be required, and thus some alternative methods have been developed for measuring sound absorption [22].…”

A novel membrane-cavity-grating (MCG) meta-structure for enhancing low-frequency sound absorption

“…Low-frequency sound absorption has always been a challenging subject in noise control due to the strong penetrability of low-frequency sound waves and the weak inherent dissipation of ordinary materials. Porous materials [1][2][3][4][5][6] and micro-perforated absorbers [7,8] as traditional solutions, according to classical acoustic theory, usually have a structural thickness equivalent to the working wavelength, which hampers their potential application in low frequency. Compared with traditional materials, acoustic metamaterials [9,10] * Authors to whom any correspondence should be addressed.…”