The time sequential variations of sound pressure levels and frequency characteristics of the traffic noise of different origin were measured on the sidewalks; regarding each traffic noise as a point source and applying equally-spaced vehicle model, we obtained theoretical formulas for variation of traffic noises as functions of time sequence, distance from lane and traffic volume. The results were as follows. 1) By frequency characteristics the traffic noise could be classified into three groups. The first group included the noises of autobicycles, motor scooters and tricycle trucks, whose octave band levels showed a peak value in 300-600 cps band(i. e. middle-frequency noise); the second group included the noises of automobiles, motor busses and trucks, whose octave band levels showed almost constant value up to 75-600 cps octave bands and slowly decreased as the frequency became higher; the third group represented the noise of streetcars whose octave band levels showed a slow peak in 300-600 cps band. 2) The noises radiated from a single car under running conditions could be regarded to have transmission characteristics of a point source. 3) The sound pressure level of tricycle trucks and passenger cars increased proportionally with the increase of car speed. The sound pressure level of autobicycle noise showed the same tendency up to 30km/hr, and increased slowly beyond 30km/hr. 4) We found theoretical formulas which express the variations of sound pressure level of street noise caused by traffic. It was ascertained that the observed data agreed well with the calculated values. By the increase of the distance from lane, the decrease of maximum sound pressure level (SPLmax) can be expected from the formula, but the decrease of mean, median, and minimum sound pressure level (SPLmean, SPLmed, and SPLmin) cannot be expected. Provided that the distance from observation point to lane is sufficiently long as compared with vehicle spacing, SPLmean increases by 3 dB when the traffic volume is doubled.
This paper describes the method of extraction of formant frequency from digitalized speech spectra by a computer program and its application to natural speech materials. Moment calculation method was employed for the formant frequency extraction, paying special attention to the separation of the first from the second, and the second from the higher formant frequency ranges. The parameters F^^^- and F_<2e> were used in this separation, where F^^^- is the first order moment of the speech spectrum and F_<2e> is the ratio of the second order moment to the first order moment of spectrum. After properly separating frequency ranges of each formant, the formant frequencies are calculated as the first order moment (average frequency) within these separated portion of the spectrum. The comparison of formant frequencies extracted from natural speech with corresponding spectrograms and the results of analysis of errors proved that this method gives acceptable results in actual speech analysis. The results can be regarded as the first approximation of formant frequencies and will form the basis of more detailed analysis such as "analysis by synthesis" or of future study on segmentation and recognition of Japanese monosyllables.
As a standard sound source for free field measurements of electro-acoustic transducers, spherical sound sources are proposed. Constructions and characteristics of these sound sources are shown, and the diffraction of sound wave due to various baffles are investigated. They are of electrodynamic type with metallic convex diaphragm and spherical rigid baffle. First, two types of spherical sound sources are described. The displacement-frequency characteristics of their mechanical vibrating systems were found to be fairly mass-controlled. The free field response is axi-symmetrical, and calculated on the assumption that its acoustic behavior is same as that of spherical sound source in which only a circular part of spherical surface vibrates uniformly in the direction perpendicular to the centre surface of the circular part. Both measured and calculated free field response are demonstrated, and it was shown that an agreement between two values is fairly good. In the second part, instead of standard sources, condenser microphones MR-103 were used as sound source, and the effect of baffles of various shapes on the sound field were examined experimentally. From the results of the experiments, it was shown the shape of baffle near the diaphragm affects sound field considerably even at a distance, and it was concluded that, for designing standard sound sources, the diffraction by baffle shapes must be taken into account as well as diaphragm characteristics.