日本音響学会誌
Online ISSN : 2432-2040
Print ISSN : 0369-4232
30 巻, 4 号
選択された号の論文の7件中1~7を表示しています
  • 今井 章, 伊藤 毅
    原稿種別: 本文
    1974 年 30 巻 4 号 p. 211-218
    発行日: 1974/04/01
    公開日: 2017/06/02
    ジャーナル フリー
    Many double wall systems have been used as light weight sound insulators, but their transmission losses (T. L. ) are little at a lower frequency in comparison with too large at a higher frequency. It is wellknown that the T. L. of a single wall takes the mass law. But the measured T. L. of a double wall is larger than the calculated T. L. , assuming that the T. L. is maximum for a infinite double wall at any incident angle. To study the difference between measured and calculated T. L. and possibility to improve T. L. at lower frequency, the vibration level on both the walls and the sound pressure level in the airspace were measured on double plaster board walls, 0. 1, 0. 2, 0. 4 m in thickness. The difference in the measured values between maximum and minimum was more than 20da in the airspace, because the lateral standing wave was excited. The distribution of vibration on the receiving wall was correlated with that of the sound pressure in the airspace (Fig. 4). The natural frequency f_imn in the finite airspace of double wall is higher than f_imn' in the case of the rigid walls. Its relation is shown in Fig. 5. In the finite sized airspace, the sound wave must be in modes, in Eq. (4), in order to satisfy the boundary condition at the edge. Any incident wave can be developed in the mode which will satisfy the condition of orthogonarity. Assuming that the radiation impedance is equal to the infinite wall and the impedance of the wall is mass reactance only, the vibration and the sound pressure are in the same mode. The T. L. can be calculated for each mode as shown in Eq. (10) and Fig. 8. For the oblique and random incidence, the T. L. of the double wall with finite sized airspace is presented by the summation of each mode as shown in Eqs. (11) and (13), which are larger than the infinite in the frequency range from f_0 to f_1, 0 at least. The measured T. L. of double plywood walls (Fig. 13) are shown in Fig. 12. Plywood partitions in airspace increase the T. L. 4-8 dB. Agreement between measurement and theory was qualitatively obtained as in Fig. 11. As for the double wall, it was shown that an improvement in T. L. is possible by the partition in the airspace.
  • 長谷川 秋雄, 能本 乙彦, 菊池 年晃
    原稿種別: 本文
    1974 年 30 巻 4 号 p. 219-227
    発行日: 1974/04/01
    公開日: 2017/06/02
    ジャーナル フリー
    In the Free-walled acoustic waveguides with semi-circular cross-section, the ratio of cut-off frequencies of lowest normal mode and next normal mode is given by 5. 14 : 3. 83=1. 34. The frequency interval between the cut-offs being the available range for usual measurement, theoretical analysis was performed on the acoustic characteristics of the free-walled waveguides with semi-elliptical cross-section with the aim of expanding this frequency interval. The normal modes of semi-ellipse cut along minor and major axes correspond to φ^e_11 and φ^o_11 respectively (cf. Fig. 10), and the 2nd normal modes for the semi-ellipse of both types are common and are given by φ^o_21. Experiments were performed on the semi-elliptical waveguide made of foam-polystyrol (cf. Fig. 12) and on the approximately semi-elliptical waveguide made of freely suspended vinyl sheet. The free-wall condition had been sufficiently satisfied by the foam-polystyrol as was evidenced from the coincidence of theoretical and experimental results-phase velocity -for the semi-circular waveguide (cf. Fig. 14). Fig. 15 is an example of the measurement for the semi-ellipse with eccentricity 0. 9. For the semi-ellipse cut along minor axis, φ^o_21 increases and φ^e_11 decreases as compared with the semi-circular waveguides of equal sectional area (Fig. 19), so that the frequency interval between cut-offs widens (see also Fig. 21), while for the semi-ellipse cut along major axis, the increase of φ^o_11 exceeds that of φ^o_12, thus it results in the decrease of the frequency interval between cut-offs (see also Fig. 21). By the way, the range of frequency measurement can be extended as shown in Fig. 24 by working out so as to suppress the second φ^o_21 mode by adjusting the position of a hydrophone on the axis of symmetry (nodal line of φ^o_21). In this figure, the ordinate Ф=cos^-1 c/c_p, where c is the free-medium velocity of sound, and c_p is axial phase velocity.
  • 野村 浩康, 馬場 恒孝, 宮原 豊
    原稿種別: 本文
    1974 年 30 巻 4 号 p. 228-231
    発行日: 1974/04/01
    公開日: 2017/06/02
    ジャーナル フリー
    The ultrasonic velocities of the mixtures of methanol and carbon tetracholoride were measured with a high pressure type ultrasonic interferometer at a frequency of 4 MHz. The resulting pressure was up to 300 atm. and the measuring temperature range was from -10゜C to 40゜C. The ultrasonic velocities of these mixtures increased with the increase of pressure parabolically and decreased with the temperature rise linearly. As an example to illustrate the experimental results, the pressure dependence of the ultrasonic velocities in these mixtures are shown in Fig. 1. From these results, the non-linear parameter, B/A, was determined. These values are summerized in Table 2. and shown in Fig. 2. As seen in Table 2 and Fig. 2, the non-linear parameter shows a maximum at 0. 7-0. 8 mole fraction of carbon tetrachloride. The curves of the relation between the ultrasonic velocities and the mole fraction of carbon tetrachloride are a minimum in all pressure and temperature ranges. The mole fraction at a minimum showed, x_min, shifted to the carbon-tetrachloride side with increase of the pressure and to the methanol side with increase of the temperature. (Fig. 5).
  • 鎌倉 友男, 池谷 和夫
    原稿種別: 本文
    1974 年 30 巻 4 号 p. 232-237
    発行日: 1974/04/01
    公開日: 2017/06/02
    ジャーナル フリー
    It is well-known that a sound wave of finite amplitude changes its wave form as it propagates in a medium ; and consequently sounds of extraneous frequencies are generated. This sound distortions are caused by the nonlinear nature of air. In this paper, the magnitudes of sound wave distortions produced by a spherical sound source which was proposed as a standard for free field measurement (Fig. 1) are investigated. A standard source requires a greater acoustic power, which in turn requires an increased intensity of the source. Consequently the amplitude of the sound wave around the source becomes finite, so the problems on the distortion of wave by a spherical sound source arise. In analyzing this problem, a formula for the distortion factors of sound pressure which seem to be significant from the observational points of view and are defined in terms of the effective pressure ration of the second harmonic to fundamental has been derived (Eq. (16)). In particular, the Eulerian coordinates are used and the effects of viscosity and heat conduction are neglected. Next, in accordance with this analysis are calculated the distortion factors for the case where the piston of the source is sinusoidally vibrating in Lagrangian sense (Eq. (17)), and several examples are shown in Figs. 2〜5. From these numerical results, it is shown that the distortion of sound pressure is considerably influenced by the variation of observation points and the magnitude of the area of piston.
  • 鎌倉 友男, 池谷 和夫
    原稿種別: 本文
    1974 年 30 巻 4 号 p. 238-242
    発行日: 1974/04/01
    公開日: 2017/06/02
    ジャーナル フリー
    Telephone transmitter is used near a mouth, Therefore an analysis of the surrounding field containing a sound source (human head) and the transmitter is necessary for design of such a electro-acoustic transducer. In this paper, the diffraction coefficient of a rigid rectangular plate near a spherical sound source has been computed to obtain the properties of a telephone transmitter of rectangular shape as shown in Fig. 4. The reason we have adopted a spherical sound source in this system is that this source can be regarded as a first approximation of human head. It is difficult to analyze the sound field in this system rigorously, and in particular the values of diffraction coefficient at the center of the plate are desired. Therefore the authors have calculated the diffraction coefficient at that point by using the Kirchhoff's approximation method and the procedure in a previous paper in case of α=β=π/2 (Fig. 5). An example is shown in Fig. 8 for a=10 cm, d=20 cm, θ_0=14. 5゜, b : c=4 : 3 and 4bc=31. 2 cm_2 (Fig. 5). Furthermore, using such parameters, the diffraction coefficient of a rectangular plate and that of a rigid circular plate of the same area is compared (Fig. 9). As a result, it is shown that the agreement of both values is acknowledged in difference by less than 0. 3 dB ; that is, it is possible to exchange a rectangular plate with a circular one.
  • 木村 翔
    原稿種別: 本文
    1974 年 30 巻 4 号 p. 243-251
    発行日: 1974/04/01
    公開日: 2017/06/02
    ジャーナル フリー
  • 岡部 昭彦
    原稿種別: 本文
    1974 年 30 巻 4 号 p. 252-
    発行日: 1974/04/01
    公開日: 2017/06/02
    ジャーナル フリー
feedback
Top