日本音響学会誌
Online ISSN : 2432-2040
Print ISSN : 0369-4232
22 巻 , 5 号
選択された号の論文の6件中1~6を表示しています
  • 久山 多美男, 菊池 年晃
    原稿種別: 本文
    1966 年 22 巻 5 号 p. 257-264
    発行日: 1966/09/30
    公開日: 2017/06/02
    ジャーナル フリー
    The refraction of sound waves in a 170m layer depth surface sound channel in the ocean is calculated by the ray theory employing somewhat simplified approximate equations (2. 8), (2. 9) and (2. 10). The depth of the bottom of the channel and the vertical gradient of the sound velociy in the channel are assumed to be 170m and +0, 015sec^-1 respectively. The reflected waves from the bottom of the ocean are neglected. The depths of the source of sound are changed by 20m steps from the surface to the depth of 160m. The rays of sound for each source depth are shown in Figs. 1, 2, . . . and 9 for the horizontal distances up to 25km and at 20' steps of the initial direction of propagation, including the up-going waves (dotted lines) and the down-going waves (solid lines) at the source. Formation of the caustics and the existence of the shadow zones are clearly indicated. It is also proposed that the sound indensity at long distances from the source in a surface sound channel, where tha ray density is uniform, will be approximately calculated by the equation (4. 1). These results will be very useful also for practical applications in underwater acoustics.
  • 菅田 成雄
    原稿種別: 本文
    1966 年 22 巻 5 号 p. 265-275
    発行日: 1966/09/30
    公開日: 2017/06/02
    ジャーナル フリー

    When underwater sound transducers are calibrated in an anechoic tank, the radio of the open-circuit output voltage of a hydrophone to voltage across the terminals of a projector must be measured. Measured values will be inevitably accompanied with errors caused by sound waves reflected from the walls of the tank. The purpose of this paper is to draw general properties of errors of this nature from an idealized simple model of an anechoic tank. The simple model of an anechoic tank is rectangular in shape (height L_1, length L_2 and depth L_3), the inside walls of which are covered with homogeneous absorbing material (Sounds pressure refletivity is independent of an incident angle. ). It is assumed that reflection from the walls of the tank is geometrical and sound waves are reflected only once. A projector and a hydrophone are placed on a line that is pallarel to the longest center axis of the tank. (1) In the case the projector and the hydrophone are both nondirectional(See Fig. 1) From Eq's 4, 9 and 11 when the center of the projector and the hydrophone coincide with the center of the tank, an error will be reduced to a minimum. Then, if Eq. 14 holds true, the output voltage of the hydrophone caused by reflected sound waves or the error will be given by Eq. 15. Also, if Eq. 16 holds true, the error expressed in dB will be given by Eq. 17, in which E_0 denotes the output voltage of the hydrophone caused by direct sounds waves from the projector, and d denotes the distance between the projector and the hydrophone. It will be senn from Eq. 15 or 17 that when the distance between the projector and the hydrophone is much smaller than the dimentions of the tank, the error will be in propotion to the distance, while the larger the dimensions of the tank are and the smaller sound pressure reflectivity is, the smaller the error is. (2) In the case the projrctor is monodirectional and the hydrophone is nondirectional(See Fig. 2) If Eq. 19 holds true, the error will be given by Eq. 20, in which G_<S1> and G_<S3> denote a sound pressure directivity factor in the θ_1 direction and θ_3 direction of the projector respectively. Also, if Eq. 21 holds true, the error expressed in dB will be given by Eq. 22. (3) In the case the projector and the hydrophone are both monodirectional (See Fig. 2) If Eq. 24 holds true, the error will be given by Eq. 25, in which G_<R1> and G_<R3> denote a sound pressure directivity factor in the θ_1 direction and θ_3 direction of the hydrophone respectively. Also, if Eq. 26 holds true, the error expressed in dB will be given by Eq. 27. It will be seen from Eq's 15, 20 and 25 that the more monodirectional transducers are used, the smaller the error is. For confirming the above mentioned results, measurements were performed in an actual anechoic tank. The anechoic tank is rectangular in shape (1. 5m × 3m × 1. 5m) and the inside walls of the tank are lined with absorbing pine wedges (See Fig. 3). Nondirectional transducers used for mesurements remain nondirectional up to about 60 kc. Also, a directivity pattern of one of monodirectional transducers is shown in Fig. 4. The block diagram of the measuring system is shown in Fig. 5. An error caused by sound waves reflected from the walls of the tank is determined as follows. When a projector and a hydrophone the distance between which is kept constant is moved along the longest center line of the tank and indicated values of the VTVM are read to calculate the average value, the error shall be given in the maximum absolute value of the difference between the average value and the indicated values. The maximum, minimum, and average values measured with a nondirectional projector and a nondirectional hydrophone in the above mentioned anechoic tank are shown in Fig. 7. The average values are on 20logd^<-1> with deviation of about 0. 2dB for frequencies of more than 10 kc (d denotes

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  • 江原 史郎
    原稿種別: 本文
    1966 年 22 巻 5 号 p. 276-289
    発行日: 1966/09/30
    公開日: 2017/06/02
    ジャーナル フリー

    Extensive and precise measurements have been made of instantaneous sound pressure distributions concerning 44 representative orchestra music which were composed from the eighteenth to the twentieth century and frequently have been performed. Amplitude distribution F(x) of a signal X(t) is a probabilistic expression for the signal and is defined by F(x)=T_x/T where T_x=Σt_i(X&ge;x) and T is measurement time. (Fig. 1. ) The measuring equipment of amplitude distribution, of which the diagram and the performance are shown in Fig. 2 and Table 1 respectively , is designed and constructed so as to suffice the requirements derived from the satistical relations (2) and (3) to the error caused by sampling. Some preliminary experiments were conducted, to approve that the distribution of orchestra sounds has the property feasible to be measured without a considerable amount of degradation even through the conventional measuring system including microphones and tape recorders whose phase distortion is usually not much minded, and then to know about the linearity characteristic of the tape recorder. It is first found that the distribution of orchestra sounds is scarcely deteriorated by the phase distortion and is almost symmetric for either sense of the signal. Figs. 3 and 9 indicate these properties respectively. In the prestent report, although invariability with the phase distortion of the tape recorder only is presented, it is convinced, with the results of other experiments, that hardly any error is feared to be induced by other types of phase distortions. Besides these, referring to the linearity of the tape recorder shown in Fig. 4 in the case with a test material which includes wide frequency components, the maximum VU meter indication is obtained below the level of which the reproduced orchestra signal is not affected by the non-linearity to reduce the level of picked up sound. Along with these preparatory investigations, much concern is also paid in minimizing the amplitude frequency distortion. Fig. 5 - 7 show the frequency responses and tolerances of microphones and the tape recorder used. In picking up orchestra sounds for measuring material, the same unidirectional condenser microphone for broadcasting practice placed in a typical position was employed. The recording level was set, according to the maximum VU meter indication during rehearsal, at the subtracted level from the overload point of the tape recorder by several decibels to record the signal without conceivable distortion, considering the probable deviation from the peak sound pressure in rehearsal. The mesurement of instantaneous amplitude distribution was conducted only for the half-wave signal. The sound pressure level is assessed by the calibration of the microphone sensitivity. Some examples of the measured distributions are shown in Fig. 10. They are almost exponentially shaped over much of the range except in the portion at the lower level. Therefore, it seems one of the most natural ways to approximate the obtained data by the normalized composite distribution (4) consisting of three terms, the first two of which represent the exponential distributions for the high-level and low-level signals respectively, and the last, δ distribution represents such extremely low-level signals as attenuated reverberation sounds. Thus, the measured distributions are processed into the normalized distributions, each set of coefficients of which represents each form of the distribution for a particular sound of performance. As to information on absolute sound pressure, on the other hand, it is represented by both the rootmean-square pressure V and the peak-factor PF which is interpreted here as the difference between the peak and the r. m. s. level. Adding to these kinds of coefficients, the peak level in S. P. L and Trms, the percentage of time for which the signal exceeds the r. m. s. pressure are obtained. These

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  • 比企 静雄, 菅原 邦宏, 大泉 充郎
    原稿種別: 本文
    1966 年 22 巻 5 号 p. 290-291
    発行日: 1966/09/30
    公開日: 2017/06/02
    ジャーナル フリー
  • 堂下 修司
    原稿種別: 本文
    1966 年 22 巻 5 号 p. 291-292
    発行日: 1966/09/30
    公開日: 2017/06/02
    ジャーナル フリー
  • 石坂 謙三
    原稿種別: 本文
    1966 年 22 巻 5 号 p. 293-294
    発行日: 1966/09/30
    公開日: 2017/06/02
    ジャーナル フリー
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