日本音響学会誌
Online ISSN : 2432-2040
Print ISSN : 0369-4232
25 巻, 3 号
選択された号の論文の10件中1~10を表示しています
  • 水谷 博, 辻 潔, 島田 稔
    原稿種別: 本文
    1969 年 25 巻 3 号 p. 103-113
    発行日: 1969/05/30
    公開日: 2017/06/02
    ジャーナル フリー

    When an electric current passes through an excitable tissue, electrical potential of the tissue which is referred to as the "local potential" V (Hill, 1936) rises, and when V reaches a constant value U, "excitation" takes place. V reverts to its resting value when an electric current, not sufficiently strong to induce excitation, is removed from an excitable tissue. The time-constant of this decay which is assumed to be exponential, is the time-constant in terms of the rate of change of V which is independent of the particular form of the current applied. i. e. , κ is the time-constant of excitation. When an electric current passing through an excitable tissue lasts for a very short time, the threshold value of the "local-potential" required for excitation is constant. If the lasts for a longer time as in the cases of constant current near the rheobase, linearly or exponentially increasing current or low frequency alternating current, the critical value for excitation rises the threshold for a slowly increasing current is welknown to be higher than that for a rapidly increasing current. This Change in threshold is called "accommodation" (Nernst, 1908). Assuming that the rise of the critical value is caused by the rise in "local potential", the critical value will revert to its resting value when the "local potential" reverts to its resting value. The time-constant of the return of the critical value to its resting level which is assumed to be exponential is λ, the time-constant of "accommodation". when an electric current is passed through a normal ear via a salt solution in the external ear canal, the excitatory effect of alternating current varies with frequency. The curve of threshold voltage plotted against the logarithm of frequency is a "U" shaped curve with a difinite minimum. It appears that there is an optimum frequency of alternating current for excitation. Well below the optimum frequency the threshold becomes large in proportion to reciprocal of the frequency excitation becomes difficult owing to "accommodation". Well above the optimum the threshold rises in proportion to frequency the rise of the threshold is caused by the duration of stimulus being short, consequently the element of "accommodation" is represented as a high-pass network (a integral circuit). Thus we may devise a circuit analogy as shown in Fig. 4, which is usefull in obtaining a better understanding of the excitablility of the electrophonic hearing. When the voltage e=v(t) is supplied to the input of this circuit, the voltage of the output e_2 may be obtained from Eq. (3) Let us assume that when e_2 reaches a critical value e_c, "excitation" takes place. We have several facts at hand which prove that the threshold is little dependent upon pulse rate, but determined by the pulse duration, in case the pulse rate of the stimulus current in electrophonic hearing is less than about 100 p. p. s. . The subjects in this experiment were therefore stimulated with currents of low pulse rate (20 p. p. s. ). 1. Observation employing rectangular current In the circuit of Fig. 4, e_2 can be calculated from Eq. (4) if e_1 is a constant voltage E. If λ=∞ and duration t=∞, the threshold is called a "true-rheobase" in Hill's theory. If λ=∞, the differential circuit of the equivalent circuit shown in Fig. 4 can be neglected, in which case, when a pulse of amplitude E_0 with a very long duration is applied to the input, the final value of e_2 at t=∞ becomes E_0. Since E_0 is the threshold at t=∞, E_0 is equal to e_c. In Eq. (4), e_2 rises up to a maximum and then falls it takes the maximum at the time t_<max> of Eq. (5). For t<t_<max>, the threshold varying with duration t can be calculated from Eq. (6). Fig. 10 shows a comparison of computation (λ=3m. Sec. , κ=0. 3m. Sec. )

    (View PDF for the rest of the abstract.)

  • 富川 義郎, 近野 正, 和泉 裕彦
    原稿種別: 本文
    1969 年 25 巻 3 号 p. 114-121
    発行日: 1969/05/30
    公開日: 2017/06/02
    ジャーナル フリー
    This paper deals with the experimental results of th electro-mechanical filters utilizing the multiple modes of a plate. It also describes the electro-mechanical filter of composite type constructed by mechanically combining these two double resonance plates and one coupler. In the first place it is shown that some multi-mode vibrators (Table 1 and 2) are obtained by combination of the same or different modes in a rectangular or square plate having multiple resonances of bending, contour, longitudinal and other vibrations. Moreover, the multi-mode vibrators suited or not suited to construction of the electro-mechanical filter are pointed out. It is consequently concluded that the plate vibrators with double resonance modes of the second resonance (f_<B2>) in bending vibration (Fig. 1) and of the first resonance ((1, 1)) in contour vibration (Fig. 15) are most suitable for construction of the filter and for practical use. Then the filters consisting of the double mode (f_<B2>) of an approximately square plate are discussed in detail; e. g. , the construction of the filter (Fig. 1), the equivalent circuit (Fig. 2 and 3), the center frequency for the plate dimensions (Fig. 4) the method of mounting (Fig. 1c), and the characteristics of the filters are shown (Fig. 6 and 7). Secondly, the construction and the experimental results of the composite type filter consisting of two plates with double resonance modes of f_<B2> and f_<B2>' and one coupler connecting the two plates at their centers are described (Fig. 8, 9 and 10). By means of cutting off the corners of a square plate, the orthogonal double mode is also obtained, and the pair of the new double mode has orthogonal nodal lines in the direction of the diagonal of the square plate (Fig. 11 and 14). Experimental results of the filters consisting of the diagonal double mode mentioned above are also shown (Fig. 12, 13 and 15). Lastly, Experimental results of the filters utilizing the two lower resonance modes of a vibrator of H type construction are described (Fig. 16 and 17). These filters are suitable for lower frequencies (Fig. 18 and 19). The filters described in this paper which utilize the double resonance mode of a vibrator are favorable for practical use and suitable for miniaturing an electro-mechanical filter. The filters will be introduced in near future into such active IC-component parts as ampli-filter and modulator.
  • 奥田 襄介
    原稿種別: 本文
    1969 年 25 巻 3 号 p. 122-129
    発行日: 1969/05/30
    公開日: 2017/06/02
    ジャーナル フリー
    To express the noise reducing effect of a muffler in terms of the difference in the sound power levels radiated from the tailpipe exit with and without the muffler in the system, equations are deduced by means of the four-terminal constants (A B C D) of the equivalent electrical network of the whole muffler system. As a result, the effect L, in dB, is expressed by Eq. (12), and L_s in the equation are given by Eqs. (13) and (14) for constant pressure and constant velocity sources, respectively, where R_2 is the acoustic radiation resistance of the tailpipe exit and Z_1 is the characteristic impedance of the input-pipe, and terms with prime denote the quantities without the muffler. In the case of expansion chamber type mufflers, L_s are simplified as Eq. (20) or (21). by assuming that the cross-sectional area ratio of the chamber to the tailpipe is considerably large. In these equations, as illustrated in Fig. 3, it seems as if the input-pipe and the tailpipe are terminated by zero impedances and the exit of the chamber is closed. And the behavior of the chamber is represented by the term, 20log|Y_fZ_3|, where Y_f is the equivalent open-circuit transmission admittance of the chamber and Z_3 is the characteristic impedance of the tailpipe. For some typical cylindrical chambers, the explicit forms of 20log|Y_fZ_3| are shown is Tables 1 and 2, where it is assumed that the sound wave is a plane wave progressing in the direction of the axis . In the low frequency range, since each element of the muffler system may be regarded as a concentrated constant element, L_s are represented by Eqs. (22) and (23). L, L_s and 20log|Y_fZ_3| are very simple, and their curves as a function of frequency are easily obtained by graphical method as illustrated in Fig. 4. When a loudspeker is used as the source, the measuring systems of 20log|Y_fZ_3| and L are illustrated schematically in Fig. 5 and 6, and the curves are obtained from Eqs. (30) and (31) by the same method as illustrated in Fig. 4. Even if the shape of the chamber is complicated, the curve of 20log|Y_fZ_3| is obtained experimentally by the same process. The results are shown in Fig. 7 and 8. Measured curves are in good agreement for practical use with those by graphical method so far as the sound wave in the chamber can be regarded as a plane wave. In the higher frequency range above the lowest resonance frequency in the direction perpendiculer to the axis of the chamber, the sound wave can not be regarded as a plane wave, and the noise reduction may not be expected.
  • 米川 元庸, 太田 悟
    原稿種別: 本文
    1969 年 25 巻 3 号 p. 130-140
    発行日: 1969/05/30
    公開日: 2017/06/02
    ジャーナル フリー
    Mechanical components in telecommunication equipments have many moving parts accompanying collision. In these equipments, rebounding after collision should be minimized for the purpose of high speed operation. Coefficient of restitution is mainly affected by two factors: the local energy loss at the impact point and the energy loss due to wave propagation. In the present paper we investigated the impact force, contact time and the coefficient of restitution when a sphere impinges upon a rod to the longitudinal direction, and obtained the rebound characteristics due to the loss of wave propagation. In the case of a sufficiently long rod in which the reflected wave does not return during the contact time, the vibration model can be expressed as series connection of s_0 and z_0 as shown in Fig. 1 where s_0 is the stiffness of local defomation at the impact point and z_0 is the characteristic impedance of the rod. In this case, the rebound characteristics are determined by a single parameter δ=mω_s/2z_0 ( m is a mass, ω_s=√<s_0/m>). In the case of a Hertz contact, if we put s_0=k^<4/5>ξ_0^<2/5>m^<1/5>, the parameter δ is equal to one half of the inelasticity parameter λ introduced by C. Zener. Stiffness s_0(=k^<4/5>ξ_0^<2/5>m^<1/5>) is regarded as the equivalent linear stiffness of the Heltz contact. Next, the coefficient of restitution (Fig. 7), contact time (Fig. 8) and peak impact force (Fig. 9) were calculated in the case where the length of rod is short and the reflected wave appears during the contact time. In this case, besides δ we have to consider the parameter S=ω_s/ω_1 (ω_1=fundamental angular frequency of the rod). δ is a parameter to represent the cross-sectional area of the rod and the parameter S represents the length of the rod. From Fig. 7 we see that, when a sphere impinges upon the end of a free-free rod, the coefficient of restitution is determined only by mass ratio M_0(=mass of the rod/mass of the sphere) so long as S<0. 3. This means tha the rod can be regarede as a concentrated mass if S<0. 3. When a mass impinges upon a free-fixed rod, the coefficient of restitution is nearely equal to 1, if S<0. 4. This means that the rod can be regarded as concentrated stiffness if S<0. 4. Comparison of the analytical results between the case where the stiffness of local deformation is linear and the case where the Heltz theory holds, shows a close agreement in the coefficient of restitution, but a slight difference in impact force.
  • 武平 信夫
    原稿種別: 本文
    1969 年 25 巻 3 号 p. 141-
    発行日: 1969/05/30
    公開日: 2017/06/02
    ジャーナル フリー
  • 渡辺 武
    原稿種別: 本文
    1969 年 25 巻 3 号 p. 142-143
    発行日: 1969/05/30
    公開日: 2017/06/02
    ジャーナル フリー
  • 田中 清, 重永 実
    原稿種別: 本文
    1969 年 25 巻 3 号 p. 144-
    発行日: 1969/05/30
    公開日: 2017/06/02
    ジャーナル フリー
  • 大泉 充郎
    原稿種別: 本文
    1969 年 25 巻 3 号 p. 145-152
    発行日: 1969/05/30
    公開日: 2017/06/02
    ジャーナル フリー
  • 原稿種別: 本文
    1969 年 25 巻 3 号 p. 153-161
    発行日: 1969/05/30
    公開日: 2017/06/02
    ジャーナル フリー
  • 中島 平太郎
    原稿種別: 本文
    1969 年 25 巻 3 号 p. 169-
    発行日: 1969/05/30
    公開日: 2017/06/02
    ジャーナル フリー
feedback
Top