This paper introduces a calculation method which evaluates noise reduction caused by barriers considering various ground effects. It is necessary to take the problem of sound diffraction and sound propagation over the ground surface into account in order to obtain the solution of noise reduction by barriers installed on the ground. Our pro posingmethod, in view of practical use, indicates that noise attenuation by diffracted wave and that of ground-reflected wave (including ground wave) are calculable inde pendently, hence the total noise attenuation by barriers on the ground should be pre sentedwith a simple numerical expression. Good agreements are found between calculations and model experiments as well as field experiments.

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The vocal tract wall impedance is considered to be related to the transmission loss in the vocal tract and to the radiation from the wall of the vocal tract, and is important in constructing an acoustic model or a circuit model of the speech production system. The wall impedance has been measured by mechanical methods before. Since the vibration of the wall is considered to be caused by the sound pressure in the vocal tract, we propose an approach for direct measurement of the reflection characteristics of the human cheek from the sound pressure distribution in a uniform tube whose end is fixed on the cheek surface. We obtained similar reflection characteristics between male cheeks and female ones. Quite similar characteristics are obtained for the inner wall of the cheek and the outer. Moreover, the characteristics can be expressed by two acoustic impedance constants. Comparing our impedance parameters with those reported by some other researchers, ours are relatively smaller. We also show the effects of our impedance parameters on the transfer characteristics of the vocal tract.

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The impact noise radiated from a circular plate which is struck by a ball is studied experimentallyand theoretically. The impact sound of a plate viscoelastically supported at its edges is compared with that of a clamped plate. The followings are found: The impact sound of the viscoelastic support consists of the initial peak and the free vibrationsound, and this is similar to the clamp condition. The viscoelastic support is effective to reduce the maximum level of the impact sound, when the plate is thin in comparison with its diameter or the level of the free vibration sound is sufficiently higher than that of the initial peak. Further there is an optimal value of the stiffness of the viscoelastic material to minimize the impact sound. However the viscoelastic support is not effective to reduce the maximum level of the impact sound, when the plate is thick in comparison with its diameter or there is little level difference between the initial peak and the free vibration sound.

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The harmonic components of finite-amplitude focused sounds emitted from a Gaussian source is examined by theory and experiments. Assuming that the radial distributions of amplitude and phase for each harmonic component are independent of the excitation level, the simplified equations for Fourier coefficients to express the distorted sound are derived. The equations were numerically solved by finite difference method to get the amplitudes and phases of harmonic components. The waveform was observed at different positions in the focused Gaussian beam realized by a circular concave piezo electrictransducer with a back electrode fabricated in the shape of star. The experi mentalresults for the first four harmonic components agreed well with the computed results. The present computation is convenient for analyzing the finite-amplitude focused Gaussian beam.

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Recently many researches and developments have been intensively made on ultrasonic actuators, because of their merits such as compactness, simple structure, and high responsewith controllability. For the realization of ultrasonic actuator, the edge of actuator with elliptic or oblique locus is needed. Recently, the authors have devised a new driving principle of ultrasonic actuator. By this principle, the coupled vibration of longitudinal vibration and flexural vibration excited by non-linear joint of the bars. According to the devised principle, a vibrator was manufactured using multi-layered piezoelectric actuators and aluminum bars. By the LDV method, the vibration locus of the vibrator edge was confirmed to be elliptic. The operation characteristics of the ultrasonic linear actuator was measured as ca. 30 cm/s at the driving voltage of 15 V.

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