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29 巻, 3 号
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高橋 賢一, 曽根 敏夫, 二村 忠元原稿種別: 本文
1973 年 29 巻 3 号 p. 131-138
発行日: 1973/03/01
公開日: 2017/06/02
ジャーナル フリーTransfer funcion in a room is approximated to a stationary Gaussian process, if the direct transmission of sound from the source to a receiving point is negligible. The impulse response in a room, therefore, is considered as a Gaussian process, since it corresponds to the inverse Fourier transform of the transfer function. Gassian process, in general, can be described by an auto-correlation function and a mean value of the process, and hence the auto-correlation function of the impulse response gives an expression of the statistic property of the sound field in a room considering the fact that the mean value of the process is zero. Since the auto-correlation function has a relation of the univalent correspondence with the ensemble average of the short-time power spectrum of the impulse response(Eq. 10), eventually the ensemble average of the short-time power spectrum is available the description of the statistic property of sound field in a room. It has an advantage in that it is characterized by the decaying aspects of sound and their dependence on frequency. The ensemble average of short-time power spectrum, therefore, is very useful for the investigation of acoustical property of room. The ensemble average of the short-time power spectrum can be deduced from the space and time averages of the short-time power spectrum of the impulse response in a room(Eq. 11)and the accuracy of the estimation may be represented by means of the normalized variance of the averages(Eq. 14). The relationship between the normalized variance of the averages of the short-time power spectrum of the impulse response and the average frequency band width of its short-time power spectrum can be expressed by the integral of its auto-correlation function(Eq. 18). The resultant formula is approximated to the following:σ_r^2=(1+2l/λ)^<-1>(1+WeqT_R')^<-1>(47)where l is the average length, λ is the wave length, Weq is the frequency band width of the short-time power spectrum(Eq. 39)and T_R' is the equivalent duration of time average(Eq. 46). Experimental results show a good agreement with the theoretical ones(Figs. 1, 2, 3, 4, 5).抄録全体を表示PDF形式でダウンロード (852K) -
森広 芳照, 森 栄司原稿種別: 本文
1973 年 29 巻 3 号 p. 139-143
発行日: 1973/03/01
公開日: 2017/06/02
ジャーナル フリーUsually, a vibration system with a circular crosssection has been used for transmission of ultrasonic torsional vibration energy, but that with a rectangular crosssection is also of use, as the case may be. A static solution concerning the torsion of a prismatic bar was completely given by Saint-Venant. In this paper, the authors derived an equation of motion(Eq. (4))and K_x in Eq. (4)is given from the Saint-Venat's solution on the assumption that the torsional wave is propagated only to the direction of x-axis and the crosssection is twisted uniformly with a definite angle θ_x(Fig. 1). From this equation of motion, in the case that the cross section is uniform in dimensions(2b×2a)along x-axis, the following expressions were obtained:(1)Velocity of torsional wave in Eq. (12)and Fig. 3. (2)Frequency equation and distribution functions of rotary displacement and twisting moment in Eq. (14). (3)Maximum shearing stress in Eq. (16)and Figs. 7 and 8. And the values of these expressions are determined not only by the material constant but also by the value of 'b/a', which is given by the dimensions of crosssection. Further, we have actually measured the torsional resonant frequencies about some test specimens shown in Table 1, using the non-contact electromagnetic type torsional vibration exciter/detector which was already reported by the authors(Reference(4)). From the experiments mentioned above, the following results were obtained. The deviation of the measured velocity of torsional wave from the calculated value is(1)less than 1. 0 percent when the ratio b/a is up to 6 for 2b/λ=0. 27(at half wave resonance)as seen in Fig. 4 and Table2, (2)less than 2. 0 percent when 2b/λ is up to 0. 5 for b/a≦3 as seen in Fig. 5, and(3)less than 1. 0 percent when 2b/λ is up to 0. 8 for b/a=1, namely the cross section is of square form. Therefore, considering the accuracy of machining and the deviation of acoustical characteristics of the materials and so on, the method of analysis mentioned in this paper was confirmed to be available for designing a torsional vibration system for ultrasonic power applications, because in such cases the dimensions of the crosssection(2b×2a)are usually smaller than the wave length(λ)and a rigorous design is not always required.抄録全体を表示PDF形式でダウンロード (473K) -
加川 幸雄, 坪田 広信原稿種別: 本文
1973 年 29 巻 3 号 p. 144-150
発行日: 1973/03/01
公開日: 2017/06/02
ジャーナル フリーCircular vibrator sensors for the measurement of atmospheric pressure, temperature and humidity by means of their natural frequency change have been developed. Uniform pressure over a circular plate supported at the edge causes the axisymmetric deformations to be a quasi shallow spherical cap, which results in the natural frequency change. The practical examples are shown in Fig. 1 where example(a)is for the atmospheric pressure measurement. For temperature or humidity, a similar deformation effect is achieved when bi-material arrangement is employed for the plate. The bi-material is composed of two thin layers with different thermal or humid expansion coefficient bonded together. That is, the higher expansion in one layer due to temperature or humidity change results in bend to form a quasi shallow spherical cap. In this case, the boundary condition at the edge must be other than "clamped". Examples(b)and(c)in the figure is for the temperature or humidity measurement. Example(b)is the case "simply supported" and example(c)"free". Two electrostrictive transducers are provided on both surfaces of the plate. One is to drive the flexural vibration while the other to receive. This is a sort of narrow bandpass electromechanical filters(See Fig. 3, 7 and 10). Proper connection of a reasonable amplifier between the transducers causes oscillation at the natural frequency of the sensor which changes with pressure, temperature or humidity. It is seen in Figs. 4 to 9 that change of the natural frequency is linear against pressure, temperature or humidity over relatively wide range, and the sensitivity is practically large enough. Sensors are suitable for felemetering and digital measurement applications. Theoretical estimation together with the experimental results is also discussed.抄録全体を表示PDF形式でダウンロード (627K) -
安藤 四一, 設楽 貞樹, 前川 純一, 城戸 健一原稿種別: 本文
1973 年 29 巻 3 号 p. 151-159
発行日: 1973/03/01
公開日: 2017/06/02
ジャーナル フリーIt has been discussed concerning a computer simulation method of sound transmission in a room(M. R. Schroeder and B. S. Atal, IEEE Intern. Conv. Rec. , 150-155(1963)). This paper presents a basic conception(Fig. 1, Eq. (1))and an approaching method(Eq. (2))for acoustic design of room by computer simulation and hearing tests of the simulated sound. Based on the "Ray Theory", the sound reflection from boundaries such as walls and ceilings etc. are simulated by using the measured transfer functions. One of the methods of measuring the transfer function of the walls has been treated in previous papers as a function of the angle of incidence including uneven walls(Y. Ando. J. Inst. Electron. Comm. Engineers, Japan, 51-A, 10-18(1968)and Y. Ando, Y. Suzumura and Z. Maekawa, J. Acoust. Soc. Japan, 28, 289-298(1972)). Also, the measured acoustic centers of a human ear are demonstrated in Fig. 8 to simulate their localization. The acoustic centers correspond to the phase of the transfer function(Eq. (12))by the sound diffraction around the listener's head including the lobes, and may be regarded as a receiving point of ears. The reflecting sound waves were simulated by making the convolution of the impulse response of the wall with an encoded reverberation-free speech signals. The simulated speech signals were judged in an anechoic chamber as a function of the angle of incidence of the signal to the walls(Table 1(a), (b)). Effective duration of the impulse response of the walls is about 2. 0 msec. Some of the sampled signals of the impulse response can be ignored for convolution calculations if their absolute values are smaller than a small value ε(Fig. 12), because of their very small contributions to the output signals. This may be seen as one of the windows on the impulse response for saving the computation time. Finally, many problems arising during the investigation are pointed out.抄録全体を表示PDF形式でダウンロード (844K) -
市川 邦彦原稿種別: 本文
1973 年 29 巻 3 号 p. 160-164
発行日: 1973/03/01
公開日: 2017/06/02
ジャーナル フリーPDF形式でダウンロード (575K) -
新居 康彦, 片倉 光宏, 真船 裕雄原稿種別: 本文
1973 年 29 巻 3 号 p. 165-170
発行日: 1973/03/01
公開日: 2017/06/02
ジャーナル フリーPDF形式でダウンロード (634K) -
能本 乙彦, 森 栄司原稿種別: 本文
1973 年 29 巻 3 号 p. 171-172
発行日: 1973/03/01
公開日: 2017/06/02
ジャーナル フリーPDF形式でダウンロード (268K) -
中村 昭原稿種別: 本文
1973 年 29 巻 3 号 p. 173-176
発行日: 1973/03/01
公開日: 2017/06/02
ジャーナル フリーPDF形式でダウンロード (558K)
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