Volume 135, Issue 5, May 2014
Index of content:
- GENERAL LINEAR ACOUSTICS 
135(2014); http://dx.doi.org/10.1121/1.4869847View Description Hide Description
A fully three-dimensional coupled mode approach is used in this paper to describe the physics of low frequency acoustic signals propagating through a train of internal waves at an arbitrary azimuth. A three layer model of the shallow water waveguide is employed for studying the properties of normal modes and their coupled interaction due to the presence of nonlinear internal waves. Using a robust wave number integration technique for Fourier transform computation and a direct global matrix approach, an accurate three-dimensional coupled mode full field solution is obtained for the tonal signal propagation through straight and parallel internal waves. This approach provides accurate results for arbitrary azimuth and includes the effects of backscattering. This enables one to provide an azimuthal analysis of acoustic propagation and separate the effects of mode coupled transparent resonance, horizontal reflection and refraction, the horizontal Lloyd's mirror, horizontal ducting and anti-ducting, and horizontal tunneling and secondary ducting.
135(2014); http://dx.doi.org/10.1121/1.4871182View Description Hide Description
Multiple scattering in a poroelastic medium obeying Biot's theory is studied; the scatterers are parallel identical cylindrical holes pierced at random in the medium. The paper focuses first on the influence, on the effective wavenumbers, of the mode conversions that occur at each scattering event. The effect of the holes on the dispersion curves is then examined for two different values of the ratio of their radius to the pores mean radius. Depending on the latter, the dispersion curves of the pierced material are compared, for the fast and shear waves, with those of either a more porous medium or a double porosity medium.
135(2014); http://dx.doi.org/10.1121/1.4869688View Description Hide Description
The far field velocity potential and radiation pattern of baffled circular plates and membranes are found analytically using the full set of modal velocity profiles derived from the corresponding equation of motion. The derivation is valid for a plate or membrane subjected to an external excitation force, which is used as a sound receiver in any medium or as a sound transmitter in a gaseous medium. A general, concise expression is given for the radiation pattern of any mode of the membrane and the plate with arbitrary boundary conditions. Specific solutions are given for the four special cases of a plate with clamped, simply supported, and free edge boundary conditions as well as for the membrane. For all non-axisymmetric modes, the velocity potential along the axis of the radiator is found to be strictly zero. In the long wavelength limit, the radiation pattern of all axisymmetric modes approaches that of a monopole, while the non-axisymmetric modes exhibit multipole behavior. Numerical results are also given, demonstrating the implications of having non-axisymmetric excitation using both a point excitation with varying eccentricity and a homogeneous excitation acting on half of the circular radiator.
Estimation of the low-frequency components of the head-related transfer functions of animals from photographs135(2014); http://dx.doi.org/10.1121/1.4869087View Description Hide Description
Reliable animal head-related transfer function (HRTF) estimation procedures are needed for several practical applications, for example, to investigate the neuronal mechanisms of sound localization using virtual acoustic spaces or to have a quantitative description of the different localization cues available to a given animal species. Here, two established techniques are combined to estimate an animal's HRTF from photographs by taking into account as much morphological detail as possible. The first step of the method consists in building a three-dimensional-model of the animal from pictures taken with a standard camera. The HRTFs are then estimated by means of a rapid boundary-element-method implementation. This combined method is validated on a taxidermist model of a cat by comparing binaural and monaural localization cues extracted from estimated and measured HRTFs. It is shown that it provides a reliable way to estimate low-frequency HRTF, which is difficult to obtain with standard acoustical measurements procedures because of reflections.