日本音響学会誌
Online ISSN : 2432-2040
Print ISSN : 0369-4232
34 巻, 6 号
選択された号の論文の6件中1~6を表示しています
  • 太田 光雄, 山口 静馬, 広光 清次郎
    原稿種別: 本文
    1978 年 34 巻 6 号 p. 333-341
    発行日: 1978/06/01
    公開日: 2017/06/02
    ジャーナル フリー
    Random city noise and vibration encountered in our living environment appear as a result of the diversified fluctuations of circumstances whose social causes are more complex than pure physical ones. From the practical viewpoint of control for such environmental noise and vibration pollution, statistics, such as the median, L_5 and L_<10>(in general, L_α sound or vibration level), are very important for evaluating of human response, these statistics directly combined with the probability distribution form of random noise and vibration, as well as the lower order statistics like average, variance and L_<eq>. Thus, it is very important to establish a systematic method for evaluating the effect of noise or vibration control systems on the widely-used standard index such as L_α. In this paper, a general study has been proposed in special reference to the unified evaluation procedure of noise or vibration control systems, when the general random noise or vibration wave, having arbitrary liner and nonlinear correlation and level probability distribution properties, is passed through the various types of liner noise or vibration control system. That is, by using only a case of a noise control system as an example, the multivariate Hermite series expansion expression, Eq. (1), can be universally employed for the statistical description of the incident sound pressure wave, x(t), with arbitrary correlation and distribution properties. The transmitted sound pressure wave, y(t), from the noise control system, is then given by Eq. (3), where A(Δ___={a_<ij>})denotes a (N×K) coefficient matrix reflecting the proper impulse response and frequency characteristics of the noise control system. The multivariate joint characteristic function, m_y(θ), with respect to the stochastic vector, y( col. {y_1, y_2, ・・・, y_N}, y_i=y(t_i)), has been derived as Eq. (12) and the corresponding multivariate joint probability density function as Eqs. (21) and (22). Thus, the effect of correlation and probability distribution properties of the incident sound wave and the individual characteristics of the noise control system on the probability distribution form of transmitted sound pressure wave are reflected in the expansion coefficient, D(m_1, m_2, ・・・, m_N) (cf. Eq. (14)) and the parameters, μ_y and σ^2_<pq> (cf. Eq. (11)). The important quantity directly connected to the evaluation of practical noise control problems is the noise intensity rather than the sound pressure itself. We have given our special attention again to the univariate characteristic function, Eq. (29), with respect to the noise intensity, E. By using the integral relations, Eqs. (30) and (32), two probability distribution expressions have been derived as Eq. (34) for the incident noise intensity and Eq. (35) for the transmitted noise intensity. The application of this statistical method was considered for a simple but basic noise control system such as a single-wall, whose frequency transfer function and discrete impulse response function are given by Eqs. (36) and (37), respectively. Experimental simulation was carried out in terms of two models of the normal-incident wave and a model of a homogeneous single-wall whose time constant was chosen within 1/20〜1/80(plate surface density, m=10. 4〜41. 4kg/m^2). The corresponding experimental results are shown in Figs. 1 (a)〜(d) and 2. Figures 3 and 4 give the noise reduction effect of a single-wall in terms of the difference between the incident and transmitted noise intensity level, L_α. Thereby, we were able to observe a good agreement between theory and experimentation. As is well-known, the random-incident mass law depends upon the additive property with respect to the average noise energy, so that it holds only when the average energy of transmitted noise wave is considered. When it is especially desired to make the evaluation in terms of the probability distribution for the transmitted noise intensity, we mu
  • 川西 哲夫
    原稿種別: 本文
    1978 年 34 巻 6 号 p. 342-347
    発行日: 1978/06/01
    公開日: 2017/06/02
    ジャーナル フリー
    A frequency characteristic of traditional pickups of moving magnet type (MM type) is generally flattened by suppressing a large mechanical resonance peak of the vibrating system with a low Q pickup body. Therefore, the upper limit of frequency range is restricted by the mechanical resonance frequency, and also the transient response characteristic is not always excellent. In this paper, a new pickup of electro-magnetic type having double resonances of electrical and mechanical systems is presented. The electrical resonance frequency of the pickup body is chosen about two times as high as the mechanical resonance frequency of the vibrating system, and a so it is required that the mechanical resonance peak is small and the electrical resonance peak is large. Thereby it is expected that the frequency range of the pickup is widened up to about two times as high as the mechanical resonance frequency. The vibrating system is approximated by a mechanical model shown in Fig. 1, and an electrically equivalent circuit of the pickup body is shown in Fig. 2. Three constants of the circuit are determined from Fig. 3 and Fig. 4. The validity of the equivalent circuit is comfirmed from Fig. 5. Using Fig. 1 and Fig. 2, analysis of the pickup is carried out by means of Laplace transform. The frequency characteristic and the step response can be respectively calculated from Eq. (12) and Eq. (17). Fig. 6 which is obtained from Eq. (12) shows the typical frequency and phase characteristics of several designed pickups. Fig. 7 shows with circle marks some conditions that the frequency deviation of the pickup is within 3dB up to 1. 8 times as high as the mechanical resonance frequency, and it is known that Q of the pickup body above 3 and the damping factor of the vibrating system above 0. 5 are the necessary conditions for the new pickup. Fig. 9 which is obtained from Eq. (17) shows three typical step responses of pickups of different type having same mechanical resonance frequency (see Fig. 8), and it is known that the transient response characteristic of the new type pickup is better than that of traditional pickups of MM type. To obtain a high Q pickup body, ferrite magnetic poles are used for the body. The frequency characteristics of the body are measured and shown in Fig. 10. When the load impedance of the body is a general value, that is, 100kΩ//100pF, the Q comes to 3. 3. Fig. 11 shows a frequency characteristic of the vibrating system which is largely controlled so that the damping factor becomes 0. 5. An experimental pickup (MM type) was composed with the ferrite body and the largely controlled vibrating system, and the frequency characteristic was measured with a test record and shown in Fig. 12. Although the frequency characteristic above 50 kHz was not measured, it is manifest that a wide frequency range pickup can be produced, which possesses the response far beyond the mechanical resonance frequency.
  • 畠山 豊正, 加川 幸雄
    原稿種別: 本文
    1978 年 34 巻 6 号 p. 348-353
    発行日: 1978/06/01
    公開日: 2017/06/02
    ジャーナル フリー
    Four kinds of nematic liquid crystals, MBBA [N-(p-methoxybenzylidence)-p-n-butylaniline], N. Mix. [nematic mixture, chemical number 11900, Eastman Kodac Company], EBBA[N-(p-ethoxybenzylidence)-p-n-butylaniline] and APAPA [4'-Anisol-4-acetoxyaniline] are investigated in the following. The effect of magnetic field on the ultrasonic attenuation in nematic liquid crystals was investigated by the usual pulse-echo technique. The change in the ultrasonic attenuation with temperature is measured for EBBA and APAPA, shown in Fig. 1. For both nematic liquid crystals, abrupt increases in the ultrasonic attenuation are also observed in the vicinity of the phase transition temperature as well as with MBBA and N. Mix. . A change in the ultrasonic attentuation with the magnetic field intensity at θ=0° and θ=90° is shown in Fig. 2, where θ is an angle between the propagation direction of the sound wave and the direction of the applied magnetic field. When θ=0°, the ultrasonic attenuation increases with the magnetic field intensity until the saturated value is reached for all nematic liquid crystals measured. When θ=90°, the attenuation decreases. Since nematic liquid crystals have a positive magnetic anisotropy, the molecules are apt to align in the same direction of the magnetic field. A change in the ultrasonic attenuation with θ is shown in Fig. 3. This can qualitatively be explained by the theory given by the Harvard group. The difference of the ultrasonic attenuation at θ=0°and θ=90°in its saturated state (2000G) is shown in Fig. 4 for temperature. These values increase in the vicinity of the phase transition temperature, where the ultrasonic attenuation also rapidly increases. The ultrasonic attenuation in nematic liquid crystals are brought on a viscous effect, a thermal condition effect, intramolecular losses and the critical attenuation associated with nematic-isotropic phase transition. We have suggested from the above measured curves that the main contribution to the anisotropic ultrasonic attenuation in the nematic liquid crystals at the temperatures measured here was the viscous effect. For the MBBA, however, the intramolecular losses also may possibly contribute to the anisotropic ultrasonic attenuation. The transient characteristics of the anisotropic ultrasonic attenuation were also investigated with the magnetic field suddenly applied or removed. These "on-off" characteristics are shown in Figs. 5 and 6. The time required for the ultrasonic attenuation to reach the saturated state when the magnetic field (2000G) is "on" is a few seconds, but the recovery times to its original state when the magnetic field is "off" is much lager, and becomes shorter with an increase in temperature.
  • 辻野 次郎丸
    原稿種別: 本文
    1978 年 34 巻 6 号 p. 354-355
    発行日: 1978/06/01
    公開日: 2017/06/02
    ジャーナル フリー
  • 森本 政之
    原稿種別: 本文
    1978 年 34 巻 6 号 p. 356-361
    発行日: 1978/06/01
    公開日: 2017/06/02
    ジャーナル フリー
  • 遊佐 康弘
    原稿種別: 本文
    1978 年 34 巻 6 号 p. 362-365
    発行日: 1978/06/01
    公開日: 2017/06/02
    ジャーナル フリー
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