Tadamoto Nimura

Improvement of Hearing Ability by Directional Information

An investigation is undertaken of the ability to hear a signal sound in the presence of noise, when the signal and the interfering sound each have a directional characteristic and are separated from each other more than a certain degree, compared with the case when both are not separated. We attempt to determine through what process in our auditory system such a phenomenon occurs. We think that, when there are many sounds coming from many directions, directional information is extracted from the neural signals from both ears in our auditory system, each sound is localized in each place or direction, and a certain particular sound is selected and listened to. There is considerable difference, in the subjects ability to hear the sound, between the case in which a subject concentrates his attention on it, and the case in which he does not. For this interpretation, “attention” is introduced. It is clarified that the function that maintains the attention leads to the selective hearing of a signal relative to ...

Auditory detection of frequency transition

The thresholds for the detection of frequency transition were obtained for the tone bursts in which the frequency was linearly changed from the initial value of 1000 Hz either during almost the whole burst duration or during a portion of it. The onset of transient had various delays from the beginning of the tone burst. The burst durations were 32, 102, 302, and 1000 msec. It was found that the nearly constant thresholds were obtained for a given burst duration as long as W(=T1+13T2) was held constant, where T1 was the duration of the initial segment of steady frequency and T2 was the duration of frequency transition. The thresholds were greater when the transition occurred near the burst onset than when it occurred near the cutoff, and in the former case, the thresholds were influenced by a rise time of tone burst. The thresholds were smallest when the frequency transitions occurred in the middle of the tone burst. It is suggested that there are two mechanisms for auditory detection of frequency transiti...

On the Perception of Direction of Echo

The minimum time differences over which same two sounds coming from different directions in succession are heard separately in direction are obtained. When two clicks are used as stimuli, the second click is lateralized separately from the first click if the former lags more than 10 msec behind the latter and the second click is less than 20 dB smaller as compared with the first one. If an accessory click is inserted between these two clicks, the minimum time difference over which two stimuli are separately lateralized is longer than that in the case without an accessory click and its value amounts to 20∼30 msec. Such a minimum difference is 100∼200 msec in the case that the space between the first click and the second one is filled up with some stimuli. As one of the results, it is shown that this time difference is smaller for a sound containing more high‐frequency component than for one containing less. Moreover, when two sounds with same duration are given to each ear with an interaural time differenc...

Studies in electromagnetic fields and phase constants of a concentric line having a helical inner conductor

This paper describes a wire helix which has a coaxial shielding cylinder since in practice a wire helix is often used with a shielding cylinder. Analyses are done by wire theory. The electromagnetic field, phase constant, characteristic impedance, and attenuation constant of the shielded wire helix are necessary in the engineering field, and the first two of them are dealt with in this paper. As for the phase constant, we present the concrete results of calculations using the numerical solution by a computer.

Sound attenuation by multiple barriers

Abstract A method (tentatively called ‘the method of equivalent sound source’) of predicting the sound attenuation achieved by multiple barriers with knife edges and/or right-angled wedges is proposed. This paper shows that the sound pressure level in the shadow region behind the multiple barriers can be obtained by successively setting imaginary sound sources for respective edges and/or wedges. The locations of the imaginary sound sources are determined by means of the traditional solution for sound attenuation by a single edge. The calculated results for several kinds of small-scale model, obtained by ‘the method of equivalent sound source’, are compared with experimental results.

An analysis of the wave impedance and the attenuation constants of a concentric line having a helical inner conductor

In this paper we describe an analysis of the wave impedance and the attenuation constant of a shielded wire helix. Analyses are made by the wire theory. Helix analyses are chiefly done by the sheath theory and the tape theory, but these make models, that are infinitely thin ideal cylinders and infinitely thin tapes, so in the case where a helix wound with finite sectional area wires is used with shielding, conditions vary and it is insufficient for contributing to a design at the time when winding encounters difficulties: it is difficult to estimate the effect of the diameter of the wire on the attenuation constant α and wave impedance Z0. So the case in which the wire helix had a shielding cylinder was analyzed in this paper. The numerical results are also presented as graphs.

Personal exposure and reaction to noise in daily life

The purpose of the study is to gain a knowledge of the relation between the amount of a persons exposure and his reaction to noise in his daily life. In this paper we discuss the details of noise exposure of 416 people who live in Sendai and Tokyo. The equivalent sound level Leq is recorded every ten minutes over 24 h and Leq24 is measured, too. Some of the findings from analysis of those data are as follows: (1) There is no difference in Leq24 among areas of residence, though the difference is seen among their daily activities. Especially for workers, the amount of Leq24 is dependent on the kinds of their work and their means of commutation. (2) Average difference in value between Leq during some activities when the respondent felt annoyed and his Leq24 is found to be about 4 dB. No significant difference is seen in this average value between the noisy group (Leq during working ≧80 dbA) and the non‐noisy Group (Leq during working <80 dBA). This fact suggests that there might exist a hazard of insidious ...

Effects of leading and trailing tones on frequency discrimination of signal tones

The effects of leading and trailing tones (interference tones) on frequency discrimination of a brief tone are investigated and auditory response to the unsteady sounds is discussed. Changes in frequency discrimination were measured as a function of frequency difference between the interference and signal tone, and interval between the two tones (Δt). The results show that frequency discrimination deteriorates as Δt decreases, and the performance is significantly affected by the interference tone especially for Δt less than 20 ms, and they also show that frequency discrimination of test tone accompanied with the interference tones of the same frequency as the test tone is almost the same as in the case without the interference tones. Frequency discrimination becomes worse, however, in the presence of interference tones with the frequency slightly different from the test tone, and when the frequency of the test tone is 1000 Hz, the effect of the interference tone is maximum for the frequency difference of ...

A consideration on the loudness of impact sound

In order to investigate loudness of impact sound, the data of about thirty samples of impact sound in our daily life, were collected in prior to laboratory experiments. As the results of the analysis of these sounds, the following ranges were observed: peak level: up to 130 dBA; rise time (from start of a sound to its peak): 0.3–30 ms; decay time (from peak down to −20 dB): 5–500 ms. Referring to these findings, we designed an impact sound generator. In the experiments the effects of these factors on loudness of model impact sounds were studied by the use of the method of adjustment. The peak level of 80–100 dB, the rise time of 0.5–20 ms/60 dB and the decay time of 60–1000 ms/60 dB were treated as the experimental factors. As the results, PL dB, calculated from the peak level r.m.s. circuit with τ = 4.0 ms and 1/3 oct. band energy level was found to be an appropriate unit for loudness evaluation, and the energy of a single burst, Len, was a simple and good measure, too. [Work supported by the Ministry of Education.]