Index of content:
Volume 126, Issue 4, October 2009
- TRANSDUCTION 
126(2009); http://dx.doi.org/10.1121/1.3206580View Description Hide Description
Power series expansions in are derived for the pressure at the edge of a radiator, the reaction force on the radiator, and the total radiated power arising from a harmonically excited, resilient, flat, circular radiator of radius in an infinite baffle. The velocity profiles on the radiator are either Stenzel functions, with the radial coordinate on the radiator, or linear combinations of Zernike functions, with the Legendre polynomial of degree . Both sets of functions give rise, via King’s integral for the pressure, to integrals for the quantities of interest involving the product of two Bessel functions. These integrals have a power series expansion and allow an expression in terms of Bessel functions of the first kind and Struve functions. Consequently, many of the results in [M. Greenspan, J. Acoust. Soc. Am.65, 608–621 (1979)] are generalized and treated in a unified manner. A foreseen application is for loudspeakers. The relation between the radiated power in the near-field on one hand and in the far field on the other is highlighted.
Hybrid method for determining the parameters of condenser microphones from measured membrane velocities and numerical calculationsa)126(2009); http://dx.doi.org/10.1121/1.3203939View Description Hide Description
Typically, numerical calculations of the pressure, free-field, and random-incidence response of a condensermicrophone are carried out on the basis of an assumed displacement distribution of the diaphragm of the microphone; the conventional assumption is that the displacement follows a Bessel function. This assumption is probably valid at frequencies below the resonance frequency. However, at higher frequencies the movement of the membrane is heavily coupled with the damping of the air film between membrane and backplate and with resonances in the back chamber of the microphone. A solution to this problem is to measure the velocity distribution of the membrane by means of a non-contact method, such as laser vibrometry. The measuredvelocity distribution can be used together with a numerical formulation such as the boundary element method for estimating the microphone response and other parameters, e.g., the acoustic center. In this work, such a hybrid method is presented and examined. The velocity distributions of a number of condensermicrophones have been determined using a laser vibrometer, and these measuredvelocity distributions have been used for estimating microphone responses and other parameters. The agreement with experimental data is generally good. The method can be used as an alternative for validating the parameters of the microphones determined by classical calibration techniques.
126(2009); http://dx.doi.org/10.1121/1.3206660View Description Hide Description
Loudspeakers in virtual soundimaging systems are usually modeled as omnidirectional monopole sources. These models are, however, only an approximation for the low frequency range. This paper presents an analytical model of crosstalk cancellation systems in a free field which takes into account the scattering and spatial characteristics of the sound sources. Based on the proposed model, the effects caused by the spatial characteristics of the sound source and its misalignments on the performance of the crosstalk cancellation system are studied numerically. It is found that although the factors such as the directivity of the sound sources and the distance between the sound sources and receiver affect the performance of the system to a certain extent, the channel separation of the crosstalk cancellation system, however, is most sensitive to the misalignment of the subtended angle of the sound sources. Therefore, if highly accurate binaural cues are required in practical applications, the type and characteristics of the playback sound sources, their locations, and orientations all should be considered carefully.