The Research On Auralization In Small Enclosures

Auralization in small enclosures is a process of rendering audible, by modeling the sound field which size is close to sound wavelength. Auralization could be used to simulate sound in the design phase of small enclosures. People usually encounter many kinds of small enclosures, such as small meeting room, living room, working room, car cavity, plane cabin and submarine chamber etc. As a result, in order to improve sound environment, reduce products noise, cut cost of manufacturing sample machine and design time, many companies are urgent to simulate interior sound of products with auralization before products are manufactured. In these kinds of small enclosures, scattering and diffraction in the course of sound radiation couldn't be ignored. At present, auralization software and research fruit based on geometrical acoustics can't solve problems above. In this dissertation, the finite element method (FEM) and adaptive finite element method (AFEM) to auralization in small enclosures are presented. Relative problems are studied and some effective approaches for the problems' settlements are given. The research work in this dissertation involves the basic theory and realization process of auralization, FEM modeling, FEM modeling based on complex sound source, error estimation and AFEM modeling, fulfillment steps of sound parameters simulation and auralization software. The main contents are as follows:1) Based on the research of basic theory of auralization, the realization process of auralization is divided four phases: the modeling of sound source, sound field, listener and sound reproduction. The key problems for auralization of small enclosed-room are pointed out, that are, how to realize three modeling tasks of auralization based on wave acoustics, how to solve the consuming of big capability memory and long calculating time.2) In order to solve the scattering and diffraction of sound radiation, in this dissertation, based on Helmholtz equation and its boundary equations, modeling of three-dimensional FEM is given for computing low frequency sound transfer function in small enclosures. Computer program is written for one rectangular enclosures and one car cavity, the results are compared with that given by the mode superposition method and experiment datarespectively. The results show that the method is effective and feasible.3) Two kinds of FEM modeling, boundary condition method and lumped sound source method, are set up for complex sound source. Boundary condition method just amend a little for intrinsic FEM program, and can obtain low frequency sound transfer function of receiver based on existed FEM mesh. The big sound source is divided into some elements by lumped sound source method, in which, the biggest size of element is smaller than the smallest wavelength of sound wave. According to form of sound source in enclosures, the different type sound source is used to represent each element. This method can be deal with any complex sound source in any position.4) Posteriori error estimation based on Superconvergent Patch Recovery (SPR) is introduced, and AFEM is established according to global error estimation and local error estimation. AFEM based on global error estimate rebuild mesh according to "refinement factor". As a result, global error is distributed on every element and adaptive optimization method could be used on element. Using AFEM based on local error estimation, we can give relevant mesh on different frequency phase with required precision.5) FEM model for calculating energy density and acoustic energy is built based on work above. Different models of objective parameters, such as reverberation time, definition, clarity index and centre time are given. Sound parameters simulation is achieved. Detailed steps for the realization of auralization software in small enclosures are presented. As an example, the auralization is used in one car cavity.