The Journal of the INCE of Japan

The methods of measurement and evaluation about ground vibrations due to the Shinkansen railway were prescribed in the advice of the Environment Agency in 1976. However, the inhabitants along the railway feel and evaluate the vibration in their houses. In this paper, the vibrations on ground and in wooden houses were measured along the Tokaido Shinkansen Line in Kanagawa Prefecture. These measurement data were analyzed with the quantification theory type I. The results showed the distance from track, the vehicles form and speed, the stratum and earth structures of railway were very affective. Then the results of the analysis were used to predict the levels of vibration in wooden houses. The other actual measurement data in wooden houses were used to compare with prediction values, and that results confirmed the validity of this prediction method.

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For reduction of ambient noise disturbances in digital hearing aid system, a method for estimating the noise level and its level distribution function from compound signal of speech input and ambient noise is proposed. Here, a distribution function of short-time averaged sound pressure level is calculated. In this proposed method, the noise level is defined as a mode of this calculated function and its level distribution function is estimated only with the portion less than the mode of this calculated function. This proposed method is applied to various noise sounds and evaluated its performance. Results of this study show that (a) this method could applicable to the compound signal with signal-to-noise ratio as low as +5 dB, (b) kurtosis of the noise level distribution may be an index for measuring impulsive components in the ambient noise, (c) by dividing the input sound signal to several frequency bands and applying this method to each frequency band, it may be possible to estimate the noise level in each frequency band and its localization characteristics of impulsive components in frequency domain and (d) this method is effective on noise reduction for two samples of digital hearing aid systems.

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With the recent increases in traffic on the highways, the noise from vehicles has become a serious environmental problem along these routes. One of the measures taken to reduce the noise level less than the environmental standards is noise barriers. Due to the performance characteristics of noise barriers, a high noise shielding effect requires very high noise barriers. As a matter of fact, there are some cases where noise barriers are constructed as high as 8-m from the surface of the highway. On the other hand, various studies have been conducted to improve the shielding efficiency of noise barriers while maintaining the height at a fixed level. As a result, new noise shielding walls with absorptive cylindrical obstacles or multiple edges attached have been widely used. The authors of this paper have also worked on the development of these new types of noise barriers. We have recently developed another new type of noise barrier in which a cylindrical obstacle with an acoustically soft surface is attached to the top edge of a noise barrier. And we have now measured the performance or efficiency of the new type of soft surface noise barrier by means of a full-scale model. We have employed two methods to measure the sound shielding efficiency. One of them measures insertion loss by using band noise. The other method determines the insertion loss by measuring the impulse response. Comparatively favorable results were obtained as reported below.

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