Measuring the free field acoustic impedance and absorption coefficient of sound absorbing materials with a combined particle velocity-pressure sensor

Abstract

Acoustic surface impedance of sound absorbing materials can be measured by several techniques such as the impedance tube for normal impedance or the Tamura method for normal and oblique surface impedance. In situ, the acoustic impedance is mostly measured by use of impulse methods or by applying two-microphone techniques. All these techniques are based on the determination of the sound pressure at specific locations. In this paper, the authors use a method which is based on the combined measurement of the instantaneous sound pressure and sound particle velocity. A brief description of the measurement technique and a detailed analysis of the influence of the calibration, the source type, the source height, the sound incidence angle, and the sample size are included.

Measuring Sound Absorption: Considerations on the Measurement of the Active Acoustic Power

“…It will be referred to as the reference model hereafter.An umber of methods [5,6,7,8] assume plane wave incidence, whereas other methods consider spherical wave incidence [9,10,11,12,13,14,15,16]. Adifferent approach is applied in the in situ method by Takahashi et al [7], further studied by Otsuru [17], and Din [8].…”

Measuring oblique incidence sound absorption using a local plane wave assumption

“…Multiple methods [3,4,5,6,7,8,9,10] can be applied to determine the oblique incidence sound absorption coefficient. These methods mostly determine the specific acoustic surface impedance or the complex sound pressure reflection coefficient, using a model that typically describes the overall acoustic field in front of a planar surface of infinite extent in a semi-free field.…”

An integrated three-dimensional sound-intensity probe

“…From the measured particle velocity and sound pressure the acoustic impedance can be calculated. The in situ surface impedance technique has been proved valid in various papers [25] [26] [27] [28] [29].…”

“…a structure, material or sound source. With the use of a sound pressure sensor and a particle velocity sensor the measurement can be done in-situ [25] • Particle velocity measurement is a valuable quantity in several cases; in some situations the particle velocity signal has a better signal to noise ratio than with the sound pressure sensor. Also the particle velocity signal can be used to measure structural velocity, implying a small and contact-less measurement of vibration [73].…”