To obtain accurate impulse responses in a sound field by numerical analysis, a high-order finite difference time domain (FDTD) method was formulated on the basis of a simple Taylor expansion. The accuracy of the FDTD scheme was evaluated by Von Neumann and Richtmyer dispersion analysis. It was found that the unavoidable phase error obtained from the conventional FDTD algorithm is reduced using the high-order scheme with 8 or more reference points. When using higher orders in the scheme used in this study, the time resolution should be small to reduce the phase error. To validate the FDTD scheme for calculating the impulse response in a closed sound field, the numerical result was compared with an analytical solution obtained by the separation of variables method. It was found that the phase error for a low-order FDTD appeared as fluctuations of the arriving pulses and that the fluctuations can be reduced using the high-order scheme with a small time resolution. The accuracy of the FDTD calculation for a large-scale sound field or a long-time calculation, which we should consider when making a sound field analysis of room acoustics or outdoor noise propagation, is strongly influenced by the phase error and therefore the error should be considered when performing such numerical analyses.
In this paper, we describe a method for estimating a crack position in a concrete structure using several accelerometers. An array of accelerometers is attached to the concrete structure and an impact is made on the concrete surface using a small impulse hammer. A reflection wave is generated from the crack position if a crack exists. Conventional methods for estimating the reflection point might seem to be useful for the detection of cracks. Because the concrete structure is elastic, however, it has three wave-propagation modes: the surface-wave mode, the primary-wave mode, and the secondary-wave mode. We cannot estimate the position using conventional methods because the necessary primary-wave mode is weaker than the surface-wave mode. To estimate the crack position precisely, we have already proposed two methods for eliminating the surface-wave and side-wall reflections. However, elimination using those methods was insufficient because they sometimes indicated a peak at a position where no crack existed. Therefore, in this paper, we propose a new method for estimating the surface wave more precisely to suppress such peaks. Some experiments were carried out, yielding better results.
Because of its plane-wave assumption at measurement points, the pressure method is in essence an approximation in determining the sound power of a source. When using the sound intensity method, the measurement errors are theoretically due only to the finite number and locations of the measurement points. In the present paper, the degrees of measurement errors of the two methods are evaluated using a sound source model that comprises multiple point-like spherical sources placed above an infinitely large rigid floor. Using such a sound source model, it is possible to evaluate the measurement accuracies of the sound pressure and the sound intensity methods because the radiated sound power is exactly calculated for arbitrary distributions of point-like sources. By randomly changing the distribution and phases of the point-like sources, it is possible to evaluate the statistical aspects of errors such as mean, standard deviation, maximum and minimum errors. One application of this source model is a comparison of the sets of measurement points proposed by standards. A new set of measurement points is also proposed.
Pitch discrimination by the human auditory system of components in harmonic tones presented dichotically is studied using a bias-free index, d′. The experimental results suggest that the pitch discrimination of an individual component in a harmonic tone depends on its harmonic number and also on the presentation scheme (i.e., the way it is presented to the listener). Part of the dependence on the harmonic number may be attributed to the strength of the perceptual grouping of harmonic components due to a specific relation in frequency, such as octave relation, between the harmonic and fundamental components. The dependence on the presentation scheme may be attributed to the difference between the strength of the perceptual grouping of harmonic components presented to the same ear and that of components presented to the opposite ear.
In this paper, we examine how covering one or both external ears affects sound localization on the horizontal plane. In our experiments, we covered subjects’ pinnae and external auditory canals with headphones, earphones, and earplugs, and conducted sound localization tests. Stimuli were presented from 12 different directions, and 12 subjects participated in the sound localization tests. The results indicate that covering one or both ears decreased their sound localization performance. Front-back confusion rates increased, particularly when covering both outer ears with open-air headphones or covering one ear with an intraconcha-type earphone or an earplug. Furthermore, incorrect answer rates were high when the sound source and the occluded ear that had an intraconcha-type earphone or an earplug were on the same side. We consider that the factors that cause poor performance can be clarified by comparing these results with characteristics of head-related transfer function.
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