A new long-range focusing transducer is proposed which is constructed by applying the variable aperture technique to a conical radiator. It is shown that, although the technique was originally developed for a concave radiator, it works more effectively in a conical radiator than in a concave one. Through the theoretical and experimental examinations, it is demonstrated that a conical type is superior to a concave one especially in the focusing performance in the near region when it is operated with a limited aperture.

View full abstract

When measuring the sound absorption coefficient of materials in a reverberation room, changes of the temperature and relative humidity in the room before and after setting a test specimen can cause considerable errors especially in high frequency bands. In order to investigate the correction method for such kind of error, numerical and experimental investigations were made in this study. At first, the calculation method for the correction was investigated, and then, possible errors due to atmospheric condition change were numerically examined based on the calculation method of the sound intensity attenuation loss of air prescribed in ANSI S1. 26-1978. As the experimental investigation, a set of reverberation time measurements were made in a reverberation room, with and without a sound absorption material, under various atmospheric conditions. From those results, the sound absorption coefficients of the material were calculated by considering the effect of atmospheric sound absorption. As a result, it was found that fairly consistent values of the sound absorption coefficient can be obtained by making the correction for atmospheric sound absorption even if the temperature and relative humidity conditions vary greatly.

View full abstract

This paper describes analysis and recognition of eight Korean isolated vowels based on the distributions of formant frequencies. In the distributions of vowels on the F₁-F₂ plane, we found overlappings between the vowels /u/, /o/, /∂/ and /w/, /ε/ and /e/ overlapped heavily as if they are the same vowels. In the comparative investigation of the dialect of Seoul and Kyungsangdo, Kyungsangdo dialect showed a heavy overlapping between /∂/ and /w/. As a recognition experiment, the speaker-independent recognition with Bayes decision method was carried out for 1, 760 isolated vowels spoken by 20 speakers. A recognition rate of 81.2% correct was obtained with the formant frequencies F₁ and F₂while the rate with LPC cepstrum coefficients was only 76.4%. Normalization for eliminating inter-speaker differences showed good results for vowels uttered by speakers of the same dialect. The highest recognition rate of 99.8 % was obtained using a supervised learning method.

View full abstract

As an alternative to the present listening inspection techniques, the spectrum pattern recognition technique which automatically detects defective parts of an electric motor was studied using small AC motors. In the noise signal analysis, 1/10-octave high resolutive spectra revealed the apparent features distinguishing the five categories of the perceived noise established by listening experts. By using the predetermined reference patterns, the recognition technique correctly determined the condition of thirty samples of small AC motors. Thus, the subjective categories agreed well with the error classes confirmed by the physical measurements.

View full abstract

Ultrasonic absorption measurements in methylcyclohexane and methyl acetate have been carried out over the frequency range 0.1-10 MHz at temperatures of 5-60°C using a piano-concave resonator method which is useful for ultrasonic relaxation study around 1 MHz. The results showed a typical spectrum of a single relaxation process, from which the relaxation frequency and strength were determined. The temperature de pendence of these parameters gives the activation enthalpy (ΔH*) and enthalpy difference (ΔH) between axial and equatorial isomers of methylcyclohexane, and those between cis and trans isomers of methyl acetate. They are:ΔH*=10.0 kcal/mol, ΔH=1.8kcal/mol, and ΔH*=6.6kcal/mol, ΔH=3.4kcal/mol, respectively.

View full abstract

A vibration power pickup and its power-calculation circuits were made for use in field surveys and a method of calibrating the instrument was devised. In order to develop methods of evaluating the vibration power generated from hand-held vibrating power tools, psychological equal-sensation experiments were carried out, using continuous sinusoidal motions in the frequency range of 8-500 Hz and bursts with various cycles of a 31.5-Hz fixed frequency. Rating experiment were also done involving five successive categories of power level (PWL) ranging from 100 to 125 dBPWL. The vibration power levels of a rock-drill, a breaker and an electric grinder were measured using the power meter and their effects on human operator were estimated.

View full abstract