Interior Sound Field Subjective Evaluation Based on the 3D Distribution of Sound Quality Objective Parameters and Sound Source Localization.

Controlling low frequency noise in an interior sound field is always a challenge in engineering, because it is hard to accurately localize the sound source. Spherical acoustic holography can reconstruct the 3D distributions of acoustic quantities in the interior sound field, and identify low-frequency sound sources, but the ultimate goal of controlling the interior noise is to improve the sound quality in the interior sound field. It is essential to know the contributions of sound sources to the sound quality objective parameters.

Realization by impedance discontinuity of a unidirectional wave in a duct with harmonically perturbed uniform mean flow.

This paper presents a study of intentionally induced acoustic mode complexity in rigid-walled ducts of separable geometry and with uniform mean flow. An intermediately located perforated plate conceptualized as an impedance discontinuity is employed to maximize the acoustic mode complexity, in turn producing a unidirectional traveling wave from the source to the impedance discontinuity. The impedance of the perforated plate for realization of a unidirectional traveling wave is derived analytically and is found to be a function of the modal wavenumbers, the Mach number of the mean flow, the position of the perforated plate, and the termination impedance.

Inducing a nonreflective airborne discontinuity in a circular duct by using a nonresonant side branch to create mode complexity.

A nonreflective airborne discontinuity is created in a one-dimensional rigid-walled duct when the mode complexity introduced by a nonresonant side branch reaches a maximum, so that a sound wave can be spatially separated into physical regions of traveling and standing waves. The nonresonance of the side branch is demonstrated, the mode complexity is quantified, and a computational method to optimize side-branch parameters to maximize mode complexity in the duct in the presence of three-dimensional effects is presented. The optimal side-branch parameters that maximize the mode complexity and thus minimize reflection are found using finite element analysis and a derivative-free optimization routine.

Reconstruction of vibroacoustic responses of a highly nonspherical structure using Helmholtz equation least-squares method.

The vibroacoustic responses of a highly nonspherical vibrating object are reconstructed using Helmholtz equation least-squares (HELS) method. The objectives of this study are to examine the accuracy of reconstruction and the impacts of various parameters involved in reconstruction using HELS. The test object is a simply supported and baffled thin plate.

Reconstruction of transient acoustic radiation from a sphere.

Transient near-field acoustical holography (NAH) formulation is derived from the Helmholtz equation least squares (HELS) method to reconstruct acoustic radiation from a spherical surface subject to transient excitations in a free field. To facilitate derivations of temporal solutions, we make use of the Laplace transform and expansion in terms of the spherical Hankel functions and spherical harmonics, with their coefficients settled by solving a system of equations obtained by matching an assumed-form solution to the measured acoustic pressure. To derive a general form of solution for a temporal kernel, we replace the spherical Hankel functions and their derivatives by polynomials, recast infinite integrals in the inverse Laplace transform as contour integrals in a complex s-plane, and evaluate it via the residue theorem.