From the basic hydrodynamical equations for non-viscous fluids, the second order wave equation in Eulerian coordinates has been expanded in terms of the velocity potential. Using the solution of this equation, the particle velocity , the pressure and the density in the Eulerian sense have been calculated down to second order terms. It is shown that when the wave is propagated the time averages of he excess pressure and density at the head of the wave train increase as the head is removed from the source of sound, and that the time averages of those in the field behind the head becomes negative. Thus the mass of the whole field containing the head is conserved. Also, the streaming in the acoustic field which has been previously studied by Eckart and Markham has been re-examined.
Some results of experiments on the propagation of sound waves in sea water are reported in this paper. When a sound wave train is emitted at a point in the sea water, it travels to another point along several different paths. And the most powerful wave reaching the second point is that which takes the path that involves one single reflection at the sea bottom. But when a temperature gradient exists in the sea water, as in summer time, experimental results assume aspects different from the above general case. Some results on diffused echoes and on the fading phenomenon are also reported.
The deviation in average levels and individual readings due to different apparatus and observers when measuring the same street noise was calculated, and the author concluded the errors to be of the order of ±1db. As representative value of noise level, the median(which the author has already proposed) was once more confirmed as most likely values.
The present investigation was undertaken to study the frequency characteristics and the normal mode of vibration of viola and violoncello bodies, and to present a comparison with the results which we had reported on violins. 3 violas and 2 violoncellos were used for the experiment and the method of investigation was similar to that adopted in the previous study on the violins. It was found that the frequency characteristic curves of the viola and violoncello were similar to those of the violin and that the vibrational figures of the viola also resembled those of the latter, but that the figures of the violoncello were different. The resonance of the air cavity of the body occurred at a frequency of about 250 cps for the viola and at about 95 cps for the violoncello, which is the resonant frequency of the Helmholtz type resonator. It occurred at a frequency of about 300 cps for violin. These values were in good agreement with the values calculated from their dimensions. Frequencies of the normal mode of the violas were almost 0. 8-0. 9 times those of the corresponding mode of the violin and the values were as presumed from their sizes. As mentioned above, we could not find any vibrational mode in the violoncello which corresponded to that of the violin. We have as yet not been able to explain this satisfactorily, but we may say that the cause of the difference might have lain in the side-board vibration, for the ratio of side board of violoncello to violin is about twice as large as the ratio of surface length.
A simple method for vowel synthesis was devised and was found to be useful in physical and phonetical research of speech sounds, especially when employed in combination with sound analysis. Essentially, the system is analogous to compound filter formed by connecting several single-tuned filters in tandem, except for the involvement of noise and distortion through the use of tape recording in the process. The actual method is as follows:A source signal, such as sawteeth, is fed into suitably tuned variable tuned-amplifier, and its output recorded. In the second process this recorded sound -"step I"-is reproduced and fed into the same amplifier, now tuned to a different frequency. The output-the "Step II"sound - is recorded in its turn simultaneously. A similar process is repeated several times. The limits of this method in playing the role of compound filter, the complex frequency characteristics of which can be changed at will, are discussed. An example of the actual stages of formation of Japanese five vowels as they are formulated out of the original sawteeth is illustrated by spectra which are seen to change by steps. The tones were made by cut and try, monitoring them in each step, and trying to obtain the optimum effect. They were analysed afterwards by the sectioner of Sonagraph. The data of tunings settled empirically in this manner are given and a description is made of some of authors' experiences in making vowel sounds by this method. The formant peak positions used coincide generally with those of natural vowels, as analysed by several investigators in this country. One exception is the formant of the Japanese "u"sound, which is reported by some authors as being located at about 1-kc. This peak, appearance of which is largely dependent on individual pronunciations, and which the authors could not add in this synthesis experiment without contaminating the vowel quality, has been found a'so in some spectra of natural vowel sounds analysed by the present authors, and one instructive example is shown. The authors suspect that this discrepancy might have been due to the impossibility of adding a very sharp and yet small peak, with the method in its present form. The vowel quality of the Japanese "u" sound varies very widely, however, depending on individual pronunciators and on other factors, and the sound without the 1-kc peak appears quite natural to the ear as the one with the peak. As source vibration employed in simulating the vocal chords, wave forms other than sawteeth were also used, one example being the sound of a viola picked up by microphone. The artificial vowel sound s composed by the use of this source appeared to be very natural when heard as human voice. The authors believe that this happy result is attributable chiefly to the fluctuating nature of the viola sounds. In this connection, sonagrams of the vowel sounds transfigured from the sawteeth and viola sources are illustrated in comparison with those of natural sounds, togethor with their section patterns. The authors also suggest the possibility that components of noise , contained to an extent in the viola sounds affect the quality of the resultant limitated voice to some degree to help in making the latter approach the natural human voice. A sonagram and section patterns of "raw" viola sounds with pith inflexions are also given.