Development of 45° incident angle sound absorption coefficient test device for design of vehicle interior trim sound package Yuli Zhao RMIT University Bundoora, Victoria, Australia Laith Neima Egab RMIT University Bundoora, Victoria, Australia Weishan Chen RMIT University Bundoora, Victoria, Australia Haiqiao Wei Tianjin University, Tianjin, China Xu Wang* RMIT University Bundoora, Victoria, Australia Abstract This paper presents a new type of test device, which is the 45-degree incident angle sound absorption coefficient (SAC) test device. A V-shaped acoustic wave-guide with the two branches forming a 45 degree angle from the horizontal direction was designed to measure the sound absorption coefficient of installed trim materials. The device was also designed for the subjective evaluation and objective psychoacoustic metric target setting of a sound source. The 45- degree incident angle sound absorption coefficient test device can also be applied to the design of the vehicle interior trim materials or sound package to minimize the negative effect of interior noise. The measurement principle of the 45-degree incident angle SAC device will be introduced first, and the experiment procedure will be then illustrated. Different kinds of trim materials were tested. The measured sound pressure data was processed with the help of the MATLAB program codes, and then the sound absorption coefficient curves were calculated and plotted. The results show the 45-degree incident angle sound absorption coefficient measurement device is a useful tool for the measurement of the trim materials for their sound absorption coefficient and for analysis of their effect on the psychoacoustic performance of a sound source. Meanwhile, a psychoacoustic analysis of sound pressure data of a sound source using ArtemiS software allows for the design of a preferred sound in the device using trim materials. These have been tested by the 45-degree incident angle SAC device. Introduction A major challenge in today’s automotive industry is to provide a better environment for drivers and passengers. To use better acoustic materials for a vehicle interior, a trim package helps to build a quieter and more comfortable vehicle cabin environment, and to improve vehicle noise vibration harshness (NVH) performance. An alpha cabin and an impedance tube are two common measurement methods of sound absorption coefficient. However, the impedance tube method only measures normal incident sound absorption coefficient which tends to underestimate the field sound absorption coefficient of trim materials [1-2] , and the use of the alpha cabin measures the random incident sound absorption coefficient which tends to overestimate the sound absorption coefficient of trim materials [3]. The field sound wave incidence onto the surface of trim materials tends to have an oblique angle. So that the design of a 45 degree incident angle sound absorption coefficient measurement system is necessary to reflect the field sound absorption characteristics of trim materials. A tone burst is a short signal used in acoustical measurements to make possible the differentiating of desired signals from spurious reflections. The American Society for Testing and Materials (ASTM) has developed this method [4]. The tone-burst technique consists of the determination of the sound absorption coefficient for a material using the impulse method as a function of a sound wave incidence angle in the free field conditions [5,8-9]. Figure 1 presents the general principle of this method. This assumes that [5]:  free field conditions exist,  sound sources emit a plane wave,  the dimensions of the tested material are several times larger than the incident acoustic wave length,  the sound absorption coefficient of the rigid panel is equal to zero,  the energy losses between the tested material and the microphone do not depend on the tested material, Yuzawa [6] proposed a cancellation method for determining the oblique incident sound absorption coefficient of a wall material by means of an on-the-spot field measurement. The reflection from a sample can be obtained by combining the outputs from two non-directional microphones through a phase inverter. By comparing this with the direct sound, measured separately, the sound absorption coefficient can be estimated. Following Yuzawa [6], Mommertz [7] proposed angle dependent in-situ measurements of reflection coefficients using a subtraction technique similar to the cancellation method of Yuzawa [6]. Frequency response analysis and fast Fourier Transform were used in the estimation method used by Mommertz [7]. The 45-degree incident angle sound absorption coefficient measurement device was developed based on the methods of Yuzawa [6] and Mommertz [7]. It was designed for selection of trim materials in laboratory conditions through the measurement of their SAC. This device allows sound wave to strike the material in a 45-degree incident angle compared with that in a 0-degree or the normal incident angle with an impedance tube 1 Copyright © 2014 by ASME Proceedings of the ASME 2014 International Mechanical Engineering Congress and Exposition IMECE2014 November 14-20, 2014, Montreal, Quebec, Canada IMECE2014-36103