A 400W ultrasonic wave generator, which consists of a 14 kc rectangular type magnetostriction transducer in water bath, master oscillator and power amplifier, was constructed for the purpose of industrial development of ultrasonic treatments. Blow-holes in gypsum moulds for ceramic industry were eliminated successfully. The bottom of a glass vessel filled with mixture of water and gypsum powder was set in the water bath above the transducer. By a 1. 5 minute exposure of the ultrasonic wave, the air which had adhered to the powder was almost entirely exhausted. The mechanical strength, hardness and durability against water, after the congealment, increased considerably by the treatment. Several kind of synthetized Japanese"sake"were artificially seasoned with the same apparatus. A triangular or spherical flask was filled with the sample and was suspended above the transducer in the water. When a spherical flask of resonant size(500cc)was used, an exposure of 1. 5 minute had satisfactory effect. Statistical tests of the seasoning effect were performed at the chance of public exhibition on the aniversary memorial day of our Institute in 1950 and 1951. Many people tested the taste and flavour comparing the ultrasonically seasoned and the not yet seasoned sample. At the test in the first year, 85% of 121 people prefered the ultrasonically treated one. But the result of the similar test in the next year was 52% of 178. The effect on synthetized whisky seemed to be more distinct than that on "sake".
The ultrasonic wave produced by piezoelectric quartz plates in transformer oil was transmitted through the bottom of a glass vessel to the liquid contained in it and the radiation pressure of the ultrasonic wave was measured in the liquid with a ballance type pressure apparatus. The values of the high frequency current through the quartz transducer were obtained for various liquids while the radiation pressure was maintained at constant values in these liquids. The h. f. current required to produce a common acoustic radiation pressure in various liquids showed a very appreciable difference according to the characteristics of the liquid, and was found to be approximately proportional to the quantity √<ρ>・c of the liquid, where ρ means the density of the liquid and c the ultrasonic velocity in it. Theoretical interpretation of this phenomenon was also presented.
The problem of the scattering of sound waves by a rigid obstacle is discussed Theoretically. The wave function at an arbitrary point in space is expressed in terms of its values at the surface of the obstacle, in accordance with the boundary conditions. The result is given by an integral equation which can be solved, fllowing the J. Schwinger's method. The amplitude of the scattered waves at large distance from the obstacle is formulated in a form which is stationary with respect to small variations of the surface fields. The scattering cross section of the obstacle for a plane incident wave can be represented as proportional to the imaginary part of amplitude of waves, scattered in the direction of incidence.
The dynamic Young's modulus and the vibrational loss of various sorts of woods used for the musical instruments were measured at the air-dried state and at room temperature. The comparison was made between the properties of suitable materials and the unsuitable ones. As to the soundboards of pianos and the violins, the suitable materials were found to have small density, high Young's modulus and low vibrational loss.
The twisting effect for the Young's moduli and the internal friction of many yarns, viz, cotton, viscose rayon, nylon and wool, is observed under the constant tention. The yarns are divided into three classes roughly. (1)The case of long fibers:In the case of uniform tension for each fiber, E・σ(E is Young's modulus and σ is apparent section area)decreases with increase of the degree of twist form the beginning. In the case of non-uniform tension, E・σ increases first with increase of the degree of twist and begins to decrease at some degree of twist. (2)The case of short fibers:E・σ and the internal friction Q^<-1> are alike to the latter case of(1). (3)The case of wool:Q^<-1> has the maximum value at some degree of twist. In the both cases of long and short fibers, the increase of E・σ and the decrease of Q^<-1> are due to the increase of apparent section area of fibers uuder the non-uniform tention by twisting, and the decrease of E・σ and the increase of Q^<-1> are due to the slack of the inner fibers of yarn. The maximum value of Q^<-1>, in the case of wool, is due to the mutual friction of wool fibers.
For the purpose of getting a testing method of the acoustical characteristics of the lecture room, the test of sound articulation and sentence intelligibility in Japanese language was carried out twice in a large lecture room and once in a small class room. The dimension of the large lecture room was of 52ft(width)×69ft(length)×33ft(height). The reverberation time calculated by Eyring's formula was 5. 8sec in empty and 2. 2sec in two thirds audience. The speaker stood on the center of the platform and spoke the sounds very slowly and the sentences in usual speed of lecture. During the first test in the large room the audience were 450 middle school students. The consequence of this test was as follows. The sound articulation was about 90% in front seats and about 10% in rear seats. The sentence intelligibility was 100% in front seats and about 80% in rear seats. The relation between the sound articulation and sentence intelligibility was very complex. During the second test in the large room the audience were 650 and the other condition was the same as before. Both percentage articulation and intelligibility were better than the former. The third test was carrisd out in a small room of 25×9. 6×22 cu. ft. The audience were 37 middle school students(18 boys and 19 girls). In this test, in the first halves of sound and sentence tests the audience were looking at the lips of the speaker, and in the second halves of them they were not looking at the lips but were using the ears only. These teste were performed in quiet, lower than the noise level of 40 db, and in the noise, thyratron noise of 60 db distributed uniformly in the room. The results of these tests were as follow. The sound articulation and sentence intelligibility was 92% and 61% in quiet and when looking at the lips, 88% and 60% in noise and when looking at the lips, and 70% and 54% in noise and when not looking at the lips, The fluctuation of data was very small in sound but large in sentence. The consequence of these three tests was as follows. (1)For testing the acoustical characteristics of lecture rooms the sound articulation test is better than the sentence intelligibility test. (2)To look at the lips of the speaker is one of the most important factor in order to obtain the higher percentage articulation.
A hearing aid is not always effective to all kinds of deafness. However, it is not easy to predict its suitability in each deaf case, but it should be decided by the user himself by wearing it in his daily life. As the results of measurements of threshold of audibility with a tuning forks, audiometer and speech and as the results of articulation tests, the following facts have been found out. 1)A hearing aid is:a)effective in all cases of conductive deafness. b)effective in some cases of perceptive deafness, and not so in others. 2)In conductive deafness:a)effective when hearing loss is 20-40db(however, conversation is possible without a hearing aid. )b)remarkably effective when hearing loss is 40-60db. (conversation becomes possible by using the machine, otherwise it is very difficult. )3)When the maximum score of articulation is:a)more than 80%, conversation becomes possible by using the hearing aid. b)60-80%, conversation is slightly difficult even with a hearing aid. c)under 60%, conversation is quite difficult even with a hearing aid, and needs lip reading. d)impossible A hearing aid can be used only to supplement lip reading. 4)A hearing aid is of no use for the total deafness. 5)A hearing aid is no good if it causes dizziness, pain in ears, or unpleasantness.