This paper describes two methods of increasing the accuracy of the power spectrum estimate in the directive spectrum analyzing system by use of a moving microphone. The objective of the system is to estimate the power spectrum radiated from a specified sound source when there are some other sources. The system is composed of two microphones, one of which is fixed and the other moves along a straight line from the fixed microphone to the sound source. By giving adequate delay to the output of the moving microphone, the system estimates the power spectrum of the sound from the direction of the sound source, eliminating the effects of sounds from other directions. First, this paper presents a method of giving the delay in the frequency domain instead of the time domain, by which the accurate delay is given to the output of the moving microphone. Secondly, this paper presents a method of suppressing the side lobes with an adequate spatial weighting, by which the errors due to the sounds from other directions are decreased.

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Generally speaking, a level fluctuation of road traffic noise is brought on by various causes. It is obvious that the ultimate causes are due to a variety of noise sources, i. e., uncertain behavior of individual cars, and to some effect of the noise propagation characteristics affected by reflections and/or absorptions owing to surrounding buildings and their topographical locations. By dividing the road into a suitable number of blocks, and paying close attention to the mean value of noise intensity in each block, the mean value can be proportional to the number of cars in the block. In this paper, on the basis of the additive property of sound energy, the unified method has been proposed to estimate the inherent characteristics of noise propagation in each block in the form of a synthetical evaluation with the number of cars for each car-type, also considering the entire background noise. We have confirmed the validity of our theoretical results, not only by means of digital simulation, but also by road traffic noise data experimentally observed near Hiroshima City. The experimental results clearly show a good agreement with the values recently reported by other official groups.

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In order to evaluate community noise, the measurement of long-term noisiness is very important. However the conventional psychophysical method is inappropriate for this purpose. Using the newly developed “method of continuous judgment by category, ” the relationship between instantaneous judgment and long-term noisiness was examined. Aircraft noises overlapping background noises were adopted as stimuli. As a result, it was suggested that long-term noisiness was determined by the prominent parts of instantaneous judgment. And it was made clear that the aircraft noise to background noise ratio had much effect on the overall noisiness of aircraft noises.

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A strictly stationary random noise seldom exists in practical random phenomena such as road traffic noise over a long time interval. Furthermore, noise data in a long time interval have recently been automatically measured in the form of quantized digital amplitude level. Accordingly, in order to predict or estimate the statistics of the nonstationary noises, it will be necessary to find an advanced approach to data analysis by use of a digital computer. In this study, with reference to the actual street noise, a new trial to estimate the level distribution of the noise over a long time interval has especially been considered on the basis of the local statistics of the noise fluctuation in a short time interval. It can also be shown that the present estimation procedure is much more suitable to the noise data observed in the form of quantized levels and to any finite number of actual noise data. The validity of the proposed method has experimentally been confirmed by applying it to the street noise data observed in Hiroshima City.

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A synthesis and design of the acoustic matching layers for piezoelectric ultrasonic transducers are presented. It is shown that the acoustic characteristic impedances for matching layers arc determined from the given operating attenuation when each thickness of the matching layers is taken for the quater-wavelength. As an example, a procedure of design for two layer-type transducers is demonstrated, where theoretical bandwidth of a ceramic transducer is about 70% and maximum insertion loss is expected 1.8dB for water load. The performance of this transducer is found to be in good agreement with the theoretical prediction.

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The purpose of this investigation is to get a fundamental theory for the reduction of impact noise. The sound caused by the impact of a ball on a relatively thin circular plate clamped at its edge was investigated experimentally and theoretically and the theoretical results almost agreed with the experimental results. The impact sound in this paper is due to the forced vibration of the plate. The forced vibration problem was solved with consideration of the damping of the plate and Hertz's contact theory was also introduced to analyze the impact phenomenon. The impact force was calculated by the small increment method and the sound pressure was calculated by assuming that the point sources were distributed all over the plate surface. The influence of both impact duration and maximum impact force on the impact sound were investigated and it was found that the impact sound pressure level depends on the amplitude of the impact force histories and the frequency components of the impact sound pressure depend on the impact duration.

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The equation of motion for a flexible plate with porous layers mounted directly on its surfaces is derived by taking account of the interaction between the solid frame of porous material and the fluid in the pores. In the derivation of the equation of motion, the effects of transverse shear defbrmation and rotary inertia of the solid material itself and of rotary force by the in-plane motion of the fluid in the pores are neglected. By the use of the obtained equation of motion, the fbrmula fbr the sound transmission coefficient through the composite plate is deduced for the oblique incident plane wave. Some discussions are made upon the increases of transmission loss by the application of the porous layers on the core plate and upon the reversibility in spatial arrangement of the plate for sound transmission.

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