Katsuaki Sekiguchi

Analysis of sound field on spatial information using a four-channel microphone system based on regular tetrahedron peak point method

Abstract This paper describes the development of a sound field measurement method which is aimed at analysing spatial information of the sound field in a room. This measurement system has four microphones and each of them is installed at the apex of a regular tetrahedron. With this method spatial information of an individual wave front is analysed from the impulse response at four points which are completely synchronised. With the introduction of a deconvolution method, measuring accuracy for waveform analysis is greatly improved and the analysis becomes much faster. By using models of which the image source positions are already known, experimental studies have been conducted on the identification of sound source positions and frequency distortion by repeated reflections. Furthermore, virtual sound sources have been detected and the waveform in actual sound fields have been recomposed. The results of these experiments indicate that the measurements are accurate and the measurement method can be used effectively.

Quantitative evaluation of characteristics of an auditorium shape in horizontal cross section

The room shape of an auditorium is often classified as a ‘‘shoe‐box type,’’ ‘‘fan‐shape type,’’ ‘‘round type,’’ ‘‘surrounding (vineyard) type,’’ or other shape. The surface diffusivity index (SDI), which is an evaluation index of surface irregularities, has been proposed by Haan and Fricke, but the SDI is based on visual surveys of photographs or drawings [Appl. Acoust. 51(1), 53–69 (1997)]. Clarification of the relationship between an auditorium’s shape and its acoustic characteristics would be simplified if the auditorium shape were understood objectively rather than subjectively. Therefore, in this study, we tried to objectively obtain characteristics of a room shape in horizontal cross section using an elliptic Fourier descriptor, which can detect the periodicity of a two‐dimensional contour. Room shapes were expressed as spatial frequency characteristics calculated from their Fourier descriptors. Based on them, we can understand the amplitude of irregularities and their scale. In addition, by using principal component analysis, it is possible to understand, quantitatively, the main differences of room shapes in horizontal cross section.

Prediction of reverberation by stochastic processes in a forest: Creation of reverberation in an outdoor performance space

A forest is an outdoor space. For that reason, reverberation formulas of indoor spaces cannot be used when predicting forest reverberation. As a matter of fact, because the level decay curve of the reverberant sound produced in a forest is nonlinear, the concept of reverberation time is inapplicable. We clarified that reverberation of a forest is expressible as a Wiener process (Brownian motion), which is a stochastic process, and we derived the formula of reverberation of a forest based on that fact. In this study, Monte Carlo simulation was also carried out. Results clarified the following. (1) The energy decay curve of the reverberation sound of a forest becomes a straight line on the logarithmic scale of time and energy; its line gradient is −2. (2) At a point far from a sound source, the reverberant sound energy increases first and begins to decrease after some period. (3) When the mean‐free path is short, the sound level of reverberation becomes high. Furthermore, we devised some methods of generati...

Study on acoustic index variations due to small changes in an observation point

Acoustic index variations due to small changes in an observation point in a concert hall were studied. Three kinds of methods were used in order to measure the acoustic indexes: (1) one point measurement using a single channel microphone; (2) binaural measurement using a dummy head microphone; and (3) the regular tetrahedron peak point method using a 4‐channel microphone system. The acoustic index variations in each of the methods were analyzed. In addition, subjective experiments were performed in order to evaluate the effects of the variations. Compared to these measurements, problems with the acoustic indexes which were analyzed by each of the methods were found. One point measurement may incorrectly evaluate a concert hall.

Calculation of sound field in a room by finite sound ray integration method

Abstract The present situation in the computer simulation of a sound field within a room, such as an auditorium, is introduced here, together with the practical application and application limits of the image method and sound ray method based on geometric acoustic theory. Simultaneously, the positioning of an approximate calculation method using a finite sound ray integration method incorporating the effect of the diffracted wave is presented. The introduction is followed by examples of the application of the finite sound ray integration method for calculating the reflection characteristics of an acoustic cloud. The reverberation process in the initial non-diffuse sound field, and the acoustical criteria are indicated, and based on these the effectiveness of the method is examined.