This paper is concerned with the use of Kirchhoff's time-retarded potential boundary integral equation in the numerical calculation of the transient response in an enclosure with rigid or absorbent boundary. The sound pulse reflected from the absorbent boundary, consisted of a porous layer on a rigid backing, is calculated by using the time-dependent “impulse admittance” (inverse Laplace transform of the normal admittance). Next, the numerical integration method of Kirchhoff's integral equation and some problems arising in the calculation are discussed. Finally, transient responses for a rigid and an absorbent cubic rooms are calculated numerically by Kirchhoff's integral equation and compared with the precise results given by the image sources method.

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The finite element method is applied to acoustic field around a cylindrical tank in order to analyze the diffraction effects. The method used in this study is the so-called hybridtype infinite element method. The cylindrical tank situated in a finite domain perturbs the acoustic field radiated from a point source. The finite domain is divided into many finite elements, which are combined with the infinite elements on the inter-element boundary using an arbitrary interpolation function. The numerical result is compared with an experimental result which was obtained for acoustic field around a water tank of a thermal power plant. From these studies, it can be seen that the hybrid technique using the combined finite and infinite elements is useful for the analysis and prediction of noise around some obstacle like a water tank.

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The characteristic impedance and propagation constant of porous materials are discussed from a viewpoint of physical realizability, and new regression models based on experimental data by Delany and Bazley are derived. Modifications from their original models are so made that the impedance function satisfies the positive-real property and that the propagation constant written in terms of complex variables becomes a regular function in the right half-plane. The new models are shown to be useful for the prediction of acoustical behavior of porous materials, especially in the double-layer case, even outside the frequency range of validity of the original models.

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Empirical models for the characteristic impedance and propagation constant of porous materials given by Delany and Bazley and by the author are generalized with respect to the porosity, the tortuosity and the pore shape factor ratio. The new models have these three parameters besides the flow resistivity. For a practical use, the impedance model can be described with two parameters, the effective flow resistivity and the ratio of tortuosity to porosity. An excellent agreement with Attenborough's four-parameter model shows that the new models are useful for the prediction of acoustical behavior of a wide variety of ground surfaces.

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This paper examines whether or not distortion actually has an effect on perceived sound quality when the amount of harmonic distortion caused by a loudspeaker is near the previously reported threshold values of 2 to 10%. For this evaluation, three physical measurements and two listening tests are performed with full-range cone and horn loudspeaker types. According to correlation analysis between the two domain measurements, the total harmonics of 0.6 to 3% are in close correlation to the subjective evaluation data. As a result, the aural detection threshold for harmonic distortion is assumed to be much lower than the previously reported values. Additionally, it appears that most of the difference in sound quality can be explained by three physical characteristics; harmonic distortion, partial-space-power frequency response and dispersion index.

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Musical performances have many aspects and vary temporally. Conventional psychological methods cannot be applicable to the measurement of instantaneous and multidimensional impression of such sounds. For that, a new method termed the “method of continuous judgment by selected description” was proposed. A list of adjectives were prepared and subjects were asked to select the most suitable adjective from the list as they listened to music and input the capital letter of that adjective to a computer. Performances of Promenades in “Pictures at an Exhibition” played by three musicians were used as stimuli. Instantaneous judgments, overall judgments and physical measurements were analyzed and compared with each other. A fairly good relation was found between the overall and instantaneous impressions, but close analysis showed some discrepancy between them. Some interaction between parts may give rise to a new impression. “Tempo” of the performances seemed to be one of the most important factors to decide the similarity between performances. The possibilities of further investigation using this new method were proposed.

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