Study On Basic Theory Of Sound Quality In Structrural-Acoustic Coupled Cavity

It is very practical and meaningful to study the noise problem inside a cavity, whose application objects include driving cabs of automobile, passenger compartments of a plane and cabins of a ship. With the development of technology, although the noise level in cavity has been improved, many negative reactions still exist, which are caused by the problem of "sound quality in cavity". Sound quality includes a series of parameters, such as loudness, fluctuation strength and roughness, etc. These parameters influence the human hearing sensation in different ways. The research on sound quality in cavity has theoretical meaning and good use value for low noise and high performance cavity design. This study also has wide application prospect on other engineering problems.Analytical method is the main method used in this dissertation. Integrated with numerical method, this dissertation makes a profound research on the characteristics of interior acoustic field and sound quality in structural-acoustic coupled cavity under different boundary conditions. Based on the theory of impedance and mobility, the interior acoustic field model is established for the structural-acoustic coupled system under simply supported conditions, and combined with the Zwicker's loudness model, a model of interior acoustic field sound loudness, which is also in the structural-acoustic coupled system, is established for forecasting. and the model of the cavity interior acoustic field whose acoustic boundary condition contains sound absorption material is derived. The sound loudness distribution of three different location points in the cavity is analyzed by using the numerical calculation results. The effect of spatial position on sound intensity level, sound intensity density and critical-band level is also studied throuth taking the frequency selectivity of human hearing system into account. And the research results provide analytical method for forecasting and designing sound loudness in the structural-acoustic coupling cavity.An independent parameter-sound fluctuation strength appears when the interior sound of structural-acoustic coupling cavity is modulated by other sounds whose frequency is between 0 to 20 Hz. Using Green Function Method and modified fluctuation strength model, a new calculation model of fluctuation strength in the structural-acoustic coupling cavity is established. The effects of modulation frequency, damping ratio and the coupling plate modal density on the sound fluctuation strength are revealed. The numerical results are presented to provide forecasting method for fluctuation strength design in structural-acoustic coupled cavity.Another independent parameter-sound roughness appears when the sound is modulated by other sounds whose frequency is between 20-300 Hz. Using finite element method and modified sound roughness model, the model of sound roughness in complexly-shaped structural-acoustic coupling cavity is established. The effects of modulation frequency, modulated sound pressure level and the coupling plate stiffness on the sound roughness are revealed. The method for forecasting and controlling the acoustic roughness in the complexly-shaped cavity is presented.Subjective evaluation method of sound quality is also studied in this dissertation. Aiming at the problem that when the jury evaluates by using semantic differential method, the judgment of the evaluation results usually depend on experience, the application of grey interval is introduced to semantic differential method, and a new judgment criterion is put forward. Compared with the time-consuming paired comparison method which would lead to failure of the evaluation, a new subjective evaluation method-comparison method with criteria, which can reflect multidimensional attributions of sound quality, is established. An experiment to evaluate nine acoustic samples participated by a 10-person jury is held. A mathematic model of sound quality is established and tested to describe subjective evaluation result in quantity with psychoacoustic parameters by using multiple linear regression method.The proposed prediction model of loudness of structural-acoustic coupled cavity is examined by a rectangle cavity samples.