This paper describes the method which abnormal condition of engine is diagnosed by radiated sound from it. Tappet clearance of the exhaust valve on 4 cycle diesel engine is selected as an abnormal part. A series of experiments carried out by changing tappet clearance whose range was from 0. 1 to 1. 45 mm, and the spectral analysis of the radiated aound was made by FFT analyzer. Using the analyzed data, multivariate analysis was made to infer the degree of the clearance. Thus, ten categories (clearance) were obtained from the data, and a category which a given sample belonged to was determined by Mahalanobis' generalized distance. As the result, the ratio of cases judged correct to sample cases was 96. 9 percent when mic distance (distance from the mic to the tappet) was 3 cm. In order to minimize the analysis time, the discriminant analysis was carried out by using appointed variables, and its effect was discussed. As a conclusion, tappet clearance value by its radiated sound proved to be successfully estimated by the proposed method.
The additive model with external fluctuation factors and the multiplicative model with internal fluctuation factors are well-known as two fundamental models describing the stationary and non-stationary random phenomena in the actual engineering field. An actual stochastic systems described by an additive model in a short time interval must be very often described in a long time interval by a mixed type stochastic model containing the fluctuation of multiplicative factor, because the internal parameter of the system changes with the passage of time. In this paper, first, by introducing a mixed type stochastic model for the actual random process, a unified expression is proposed for the probability distribution function of the above non-stationary composite wave measured by an arbitrary non-linear observation system. Next, by use of the above theory, two types of new methods identifying the probability distribution function of a specific factor embedded in the composite wave are derived in a general form of series expansion expression. Finally, by applying the above theoretical results to various types of L_<eq> evaluation problems of road traffic noises and industry noises based on the actual noise observations corrupted by the background noise, the validity of proposed evaluation methods is also experimentally confirmed.
The usual type of ultrasonic transducers can not only radiate ultrasonic waves with a narrow frequency bandwidth, but it is possible to obtain a broad bandwidth by using a wedge-shaped transducer. Plano-convex transducers, which are modified wedged transducers, are made of piezoelectric ceramics having the thickness extensional vibration. The typical features of this transducer are to radiate continuous and pulsed ultrasonic waves over a broad frequency range, to transmit and receive a short ultrasonic pulse, and to radiate focused ultrasonic waves. Those features and another characteristics with this transducer is more clarified through the measurements of free impedance, radiation pattern and ringing for an impulse. As applications using the plano-convex transducer with excellent features and low noise for the pulse-echo technique, it is attempted to detect a small hole in steel(non-destractive testing), and to measure the sound velocity of the longitudinal and transverse waves in materials.
The properties of vibration on Tsuzumi, kinds of drums in Japanese traditional musical instruments, are theoretically and experimentally discussed. There are two kinds of Tsuzumi, ootsuzumi and kotsuzumi that have different features each other. First, considering the structures and materials of their membranes, it is described that the vibrations on ootsuzumi's membranes may be approximated to that of a circular membrane, and that the vibrations on one side of kotsuzumi's membranes have features of an annular membrane and those on other side have features of a loaded membrane which has the mass on the center. Next, solved the wave equations of these three membranes and derived their eigen equations, the properties of their vibrational frequencies are presumed by means of ratios of roots on the eigen equations. As a result, it is mentioned that the vibrational frequencies of ootsuzumi may approximate to ratios of roots of the Bessel's function and those of kotsuzumi may indicate harmonic properties, which are shown by comparing between the theoretical values and the measured values of their spectrum. These results may be applied to the synthesis of electronic musical instrument tones.
It has been reported by some authors that the noise reduction by an absorptive barrier is due mainly to the absorbing material attached to the narrow surface(nearly a wavelength in width) along the barrier edge. This phenomenon is very interesring, and it may be useful for the economical design of barrier. In this study, (1)We will show a method of estimating the sound attenuation by thin barrier with an absorbent strip attached to the arbitrary region of the source side surface. (2)We have investigation of the relative sound pressure level fluctuation due to variation of the width of absorbing(or reflecting) region along the barrier edge. Macdonald's formula for a thin barrier and Pierce's formula for the double edge diffraction by a thick three-sided barrier are used in this study. The calculated results for several kinds of small-scale model, obtained by present procedure, are compared with experimental results.
In order to investigate whether the different sound field causes difference in temporary threshold shift(TTS), ten young students with normal hearing acuity were exposed to broadband noise for an hour both in an anechoic room(free-field) and in reverberant room(diffuse-field). In the anechoic room, one subject was exposed to the noise faced with his right ear directly to the speaker, and in the reverberant room, two subjects were exposed at a time. The exposure noise was the white noise band-pass-filtered from 0. 9kHz to 9kHz, and the exposure levels were 80, 83, 86 and 89dB SPL, which were the same in the both field when measured by means of 1-inch free-field microphone. TTSs were measured at 2, 3, 4, 6 and 8kHz. The results showed that no significant TTSs were observed at 2kHz in either field. The growth curves of TTS at 3 and 4kHz observed in both fields were similar. However, TTSs at 6 and 8kHz in free-field exceeded those in the diffuse-field. It is estimated from the present study that the sound pressure level in the diffuse-field measured by means of the free-field microphone needs to be raised by 2. 7dB so that the TTSs at 8kHz in the both fields might be equal. Those results are consistent with the sound pressure level transformations from both sound fields to the coupler microphone of an anthropometric manikin(KEMAR manikin).