The possibility of the long range propagation of sound waves in the sea near the Okinawa Islands depends on whether or not of the existence of a sound channel. The character of the sound channel in the Western North Pacific, including the above mentioned regions, was investigated by use of the observation data of temperature and salinity by the Japanese Hydrographic Office during 1936 and 1946. The results are as follows: a) There was no sound channel in the East China Sea or the Yellow sea, but the formation of a sound shadow zone was perceptible. b) The sound channel in the Western North Pacific appears to be closely related to the Kuroshio. Especially, it is evident that the character of the sound channel in the sea southwest of Japan is greatly influenced by cold water masses, which arise frequently off Shiono-misaki, and which bear directly on the variability of the flow pattern of the Kuroshio.
The so-called "cantilever bell" is a kind of percussion instrument used mainly in a clock and consists of a straight rod of bronze or steel with a slender portion at the clamped end. The characteristics of strike tone of this instrument depend on the dimension of this portion. In this paper we investigated analytically by Cowley-Levy's method the effects of narrowing the section of rod at the clamped end on the natural frequencies of the system and obtained the general equation that determine the frequencies of overtone of this bell. From this equation it is shown that the cantilever rod with an extreme slender portion at the clamped end can be regarded as one end supported rod instead of one end clamped rod. As we well know, the overtones of the cantilever rods with uniform section are not harmonics but if the rod has the section narrowed suitably in the neighborhood of the clamped end, they harmonize partly, and also a fundamental tone is greatly decreased in frequency.
We measured the vibration acceleration at one point of the plate and the sound pressure near the plate surface, using the 2 channel magnetic tape recorder and the 1/3 octave band analyzer. These quantities decrease with time as follows; A=A_0 exp(-αt), where A is the vibration or the sound pressure, A_0 is the initial value of these, and α is the rate of damping. Attention was given to the values of A_0, and following results were obtained. 1) There is an intimate relation between the hammer momentum and the initial value of the acceleration or the sound pressure, and it is shown as the next experimental formula; A_0=K_2 mv^<K1>, where mv is the momentum of the hammer ; K_1 being the coefficient which is a function of frequency, and about 1 at lower frequencies and less than 1 at higher frequency; K_2 is the coefficient which is a function of frequency, momentum of the hammer, rate of concentration of impulsive force and the elastic quantities of the plate and of the hammer, and less than 1. We made assumption on the physical meanings of these coefficients. 2) The relations between the vibration acceleration and the sound pressure are not constant owing to the plate material and its thickness, but it is adventageous to use the accelerometer in order to measure the relations between the sound pressure and the vibration in an audio frequency range, as the acceleration correspond to the sound pressure on the whole. 3) According to the observation of wave form and contact time of the hammer by using a synchroscope, the wave form of the sound pressure is alike that of acceleration rather than that of velocity and displacement, and there is no unique relationship between the contact time and the impulsive force action time.
This paper describes the designing method of the high fidelity ribbon type microphone for broadcasting purpose which has recently been developed in our laboratory. The design objective was to obtain the wide, uniform frequency responses for all directivity characteristics: omni-, uni- or bi-directional. For that purpose, numerical relationships between elements in the acoustic equivalent circuit were clarified. Then, a few problems on manufacturing of practical product were explaned, taking into consideration the convenience of users and the simplicity of the operation of such products. The trial products based upon these considerations have a good frequency characteristics.
A new electronic digital reverberation time meter was devised, which enables to indicate automotically the average of reveberation times (Tm) observed in N repeated times. The composition is as follows: The first system is a sound pulse generator. Repetition period of a sound pulse is adjustable to be any one of 0. 5, 1, 2 and 3 seconds. Pulse duration is about a half of them. The second system is composed of level discriminating circuit and gating circuit, which makes counting pulses pass while reverberation falls through an appointed level range (adB), actually 10, 20 or 30 dB. The third system is a circuit which stops the counting when number of observations reaches N. The fourth system is a pulse counting circuit of decimal type. Frequency of counting pulse is selected to the value equal to 60/a・1/N・10^n p. p. s. , so that the counting tubes indicate Tm×10^n directly. In general it is necessary to observe a number of reverberation curves in order to obtain the reverberation time of a room with desired accuracy, so the new device can eliminate much of time and efforts comparing with a high speed level recorder which is widely used.
A novel method for computing ray paths of underwater sound for a given vertical distribution of sound velocity or temperature is presented. Equations for computing ray paths, an equation for obtaining sound intensities and an equation for determining locations of focal points are so integrated as to obtain results of adequate accuracy with minimum of redundancy and labor. Features of this method are enumerated as follows: (1) It is assumed, as usual, the propagating media may be divided into horizontal layers, in each of which the velocity gradient remains constant. It is not necessary, however, to compute values of velocity gradients itself. (2) All computations can be done on a nomograph and a slide rule without use of elaborate tables and desk calculators. (3) Subdivided horizontal layers may be added later to determine more precisely the configuration of a sound ray path without any interference to the previous computation. (4) Not only configurations of ray paths but also sound intensities, spreading loss, focussing effects, deviations from the inverse square law, equi-intensity lines and so on can be easily obtained. (5) Temperature distributions measured by a bathythermograqh can be directly used for computation without an intermediate conversion to velocity distribution, provided that depth and salinity corrections may be neglected. Detailed procedures of computation and a numerical example are described.
The qualities of stereophonic sound reproduced by binaural earphones were scaled by means of the method of paired comparison. The concepts of the quality treated here were composed of twelve different characters; vividness, richness, pleasingness, powerfulness, clearess, loudness, presence, feeling of distance, separation of signal from noise, feeling of moving sound image, and feeling of offensive reverberation. The method of experiment and method of scaling were as same as described in Report I. In this report, following problems were also treated; the first was the method of extraction of quality concepts, the second was meaning of unit of psychological scale. As the result of this experiment, a psychological scale in each qualities was obtained, and it was shown quantitatively by using these scales that the stereophonic system had character of high fidelity. As a consequence of these Reports I and II, a new method for rating higher qualities was established.