Study On Measurement Techniques Of Interior Sound Quality Contribution Analysis And Improvement

Interior noise has become one of factors affect consumer chosing which kind of vehicle. In the late seventies, requirement for driver and passenger comfort were increased significant. Since than, a large amount of efforts have been invested into the improvement of technology of noise & vibration reduction and containment. There are four aspects about noise controlling. Sound quality evaluation is useful for both quantitative analysis of the interior noise and setting the target sound. Transfer path analysis(TPA) has been an important experimental method in automobile source identification. Sound absorption material and muffler are effective and simple in noise reduction.The classical TPA techniques identify the transfer paths by isolating each path. This approach has two major disadvantages. First, the disassembling is very time-consuming. Second, the boundary conditions are not correct anymore. In the paper, an operational path analysis(OPA) technique based on partial signaular value decomposition is provided. Instead of of a load-response relationship of TPA, it is based on a response-respose relationship. The number and location of sources are identified by singular valued decomposition(SVD) and partial singular valued decomposition(PSVD). The sound quality contributions of sources are analyzed through sound quality prediction. The OPA method is verified by three source idientification experiment and applied to micro commercial vehicle body radiation sources contribution analysis.Impedance tube method and Reverberation chamber method are two main methods for measuring absorption coefficient. Impedance tube method with two microphones is usually applied to measure normal incidence absorption coefficient, while the reverberation chamber to diffuse absorption coefficient. The reverberation chamber method requires large scale of sample and Impedance tube method requires small scaled of sample. Because of wavelength limitation, the measurement using impedance tube method needs to change tubes with diameter 100 mm into 30 mm. In some practical application, some materials such as ground near airport, grassland and interior are required to be measured in-situ. In recent years, a new surface impedance method which uses a PU probe is considered to be an alternative. The method calculates absorption coefficient from surface impedance by measuring pressure and particle velocity. This paper describes the principle of the surface impedance method, and compares it with impedance tube method through measuring the absorptive coefficient of an absorptive sample. To instruct the measurement using the surface impedance method, the influences of measurement distance between PU probe and specimen, specimen size, ambient noise and sound incidence angle are analyzed. The analysis of influences gives comprehensive suggestions about the ranges of absorption coefficient, bandwidth and measurement conditions for measurement setting up.The conventional approaches for measuring muffler transmission loss based on measurement in impedance tube are mainly decomposition methods and transfer matrix method. The decomposition method needs an anechoic termination, but it is not easy in some practical cases particularly for low frequency measurement. Two-load method and two-source method based on transfer matrix techniques are considered to be an alternative approach which does not require an anechoic termination. A straightforward method for measuring muffler transmission loss by two PU probes measuring particle velocity at the inlet and outlet of muffler is presented. The four-pole parameters of the muffler can be calculated directly. The transmission loss measured by the PU method agrees well with the result measured by conventional method and FEM result. To instruct the approach, the influence of measurement distance between PU probe and the inlet or outlet of muffler and ambient noise are analyzed, which gives comprehensive suggestions for measurement set up.The paper began with NVH experiment and sound quality evaluation of micro commercial vehicle, and invested into sound source identification and nosie improvement. The Chapter one was the literature review including TPA, sound quality, absorption coefficient measurement techniques and muffler transmission loss measurement techniques. In Chaper two, NVH performances of three micro commercial vehicle prototypes and a target vehicle were analyzed. In Chapter three, sound quality was evaluated objectively and subjectively. The prediction model of interior sound quality was presented using multi linear regression method. In Chapter four, the OPA technique based on PSVD was presented. In Chapter five, the experimental research for verifying the procedure was finished, from which the source with largest sound quality contribution was picked up from three sources. For engineering application, the sound quality contributions of radiation panels to the interior noise of a micro commercial vehicle were analyzed. By investigating the contributions of sound sources to each sound quality attribute, the dominant sound source is determined. In Chapter six, absorption coefficient in-situ measurement technique and muffler transimission loss in-situ measurement technique were presented. In Chapter seven, some improvement projects based on upper research were suggested, including body structure design, body radiation panles vibration suppression, good absorbing material and motor mounting support improvement. The NVH experiment of improved prototype and original prototype shown that the noise level and loudness near co-driver ear both decrease at 4 gear 40km/h. The predicted annoyance score decreases dramatically. The chapter eight was the full paper summary and prospect.