日本音響学会誌
Online ISSN : 2432-2040
Print ISSN : 0369-4232
29 巻, 2 号
選択された号の論文の8件中1~8を表示しています
  • 柏木 英一
    原稿種別: 本文
    1973 年 29 巻 2 号 p. 75-84
    発行日: 1973/02/01
    公開日: 2017/06/02
    ジャーナル フリー
    The pulse and the standing wave methods and mainly applied to under water acoustic measurements. But in most cases where they are disturbed by external noise, it is effective to apply the correlation technique. The main advantages of the correlation method which are well known, are as follows:(1)The sound intensity can be measured without the influence of external noise. (2)If there are multiple sound paths from the emitter to the receiver, each sound ray can be measured by using continuous waves as distinctly as by the pulse method. From the cross-correlation we can detect the traveling time and the relative intensity of the sound. This paper deals with FM signals(frequency modulated waves)as a continuous signal having properties which are common to the white Gaussian noise. In the case of high modulation index, it is well known that the spectrum density of the FM signals is approximately proportional to the probability density function of the frequency-modulating process. Thus, it is expected that we can get the various spectra of the FM signal by changing the frequency-modulating process and the modulation index. Then, as a modulating signal we examined the use of a binary Poisson process(a binary random process whose successive zero-crossing intervals are Poissonly distributed). In this case the FM signal has the spectrum density as shown in Fig. 3. Therefore this method enables the equivalent bandwidth of the receiver output to be large as shown in Fig. 2, when the mechanical Q of the transducer has a high value, as in under water acoustics. Consequently, by selecting a suitable frequency-modulating process and modulation index according to the properties of the measuring system, it is possible to get a smaller separable interval of signals arriving at different times than by the pulse method in which the pulse length is determined by the value of Q. This enables us to take measurements in a small water tank. As mentioned above, using FM signals has the following additional advantages:(3)It is possible to select the spectrum density function, the center frequency and the equivalent bandwidth of the measuring signal, voluntarily. (4)Accordingly, the separable time intervals of the receiving signals can be made equivalent irrespective of the value of the mechanical Q of the transducer. (5)As the FM signal has a constant amplitude, it is easy to polarize the signal in the polarity coincidence correlation detection.
  • 柏木 英一
    原稿種別: 本文
    1973 年 29 巻 2 号 p. 85-90
    発行日: 1973/02/01
    公開日: 2017/06/02
    ジャーナル フリー
    The pulse, the sing-around and the standing wave methods are mainly applied to under water sound velocity measurements. These methods are related to the correlation method, in that the error in measurement increases as the frequency is lower when the measuring distance is fixed. Hence, we examined the system shown in Fig. 1 as a method which eliminates these weak points. This measuring system can be explained as follows:A PM signal(a phase modulated wave)is made whose modulating signal consists of the addition of the low frequency emitting signal s(t)(Gaussian noise)and receiving signal y(t), and then its auto-correlation function is computed. From this function we can detect the acoustical delay time of the phase-modulating signal s(t)+y(t). Simultaneously, the error in measurement is decided, almost independently of the frequency of s(t), mainly by the carrier frequency ω_c and modulation index m_p of PM signal whose values can be chosen voluntarily after the reception. Accordingly, when ω_c and m_p are larger, the error in measurement is smaller and when ω_c and m_p are fixed, the error is also fixed even though we change the measuring frequency bands of s(t). In other words, it means that instead of s(t), the PM signal can be considered as though it were the measuring signal. This method can be also considered to be qualitatively equivalent to the system which computes the cross-correlation function of s(t) and y(t) and amplifies it non-linearly in order to increase the resolving power, as shown in Fig. 2, 3. Besides, if the reflected sounds are a few and if the external noise contains no periodic components and its equivalent bandwidth is more than the degree of s(t), the characteristics of the correlation method are maintained in this method. Namely, we can take measurements without the influence of external noise and also distinguish the direct sound from reflected sounds.
  • 桑原 尚夫, 境 久雄
    原稿種別: 本文
    1973 年 29 巻 2 号 p. 91-99
    発行日: 1973/02/01
    公開日: 2017/06/02
    ジャーナル フリー
    In our previous study, it was found that the phonetic values of vowels taken out from a connected speech were perceptually quite different from the corresponding isolated monosyllables, and that two syllables, one preceding and one following, were necessary to provide a perceptual environment for their correct identification. These facts indicate that the perception of vowels in connected speech is seriously impaired by the complete removal of their environment. In other words, the identity of such a vowel is not only determined by locally extracted features but also by its relationship with those of the preceding and following sounds. This paper is concerned with the dynamic aspect of vowel reduction, associated with contextual influence, and the modification method by which such vowels are characterized in acoustical features using contextual information. It is assumed that the acoustical features of speech sound at any instant, are modified by the contribution of dynamic acoustical features of preceding and succeeding continuous signals, and that the extent of the effect conforms to the normal distribution function of time(Eq. (5)). Two unknown factors contained in this function were calculated from the results of the perceptual experiment by B. E. Lindblom, and the modification rule was applied to the middle vowels in /VV'V/ context(symmetric form)and in /VV'V''/ context(asymmetric form). The instantaneous first and second formant frequencies of vowels were used as the acoustical features and the modification was done obeying Eq. (8). The results were as follows:1. Normalization effect was observed for vowels in the case of the symmetric form. 2. Each vowel region in the f1-f2 diagram shifted towards the center of the distribution for all vowels as compared with the region of monosyllabic vowels and partially overlapped with each other, but vowel regions were separably located in modified f1-f2 diagram.
  • 高橋 純夫, 森 栄司
    原稿種別: 本文
    1973 年 29 巻 2 号 p. 100-107
    発行日: 1973/02/01
    公開日: 2017/06/02
    ジャーナル フリー
    The output power of electrostrictive transducers in ultrasonic power application seems to be limited by following three major factors:(1)saturation of electrostrictive driving force, (2)maximum vibrational stress amplitude not to cause electrostrictive property degradation due to large amplitude continuous vibration, and (3)mechanical fatigue limit of transducer materials. The authors have already measured the mechanical fatigue limit of transducer materials and the data about it have been presented in the previous paper. The present paper deals with electrostrictive property degradation mainly due to heat generation or temperature rise under large amplitude mechanical vibration. A method to measure continuously the change of electrostrictive stress constants h_l and e_l under large amplitude mechanical vibration is described, and the measurements were performed in order to clarify the upper limit of vibrational stress level not to cause any degradation of electrostrictive stress constants. At practical operations, dielectric loss and mechanical vibrational loss exist simultaneously in the transducer, however, because of the low value of dielectric loss factor(tanδ), dielectric loss usually remains to be small, compared with mechanical vibrational loss, except the cases in which a large electric input is required owing to a quite heavy mechanical load. Furthermore, in most cases, while dielectric loss is uniformly distributed throughout the transducer, mechanical vibrational loss depends upon the vibrational stress distribution in the transducer. In view of these circumstances, it is quite necessary to investigate the behavior of electrostrictive stress constants in connection with the vibrational stress distribution. For this purpose, the bar-shaped lead zirconate titanate transducer with three pairs of electrodes along its length was taken up, and it was used for longitudinal mode vibration, excited mechanically by another vibrating system which consists of a nickel magnetostrictive transducer, a metal resonance horn, and a vibration pick-up. Electrostrictive stress constants h_l and e_l were measured for each pair of electrodes, where values of vibrational stress differ according to the vibrational stress distribution, by the observation of open circuit voltage and short circuit current of electrodes, and this measurement was performed at a few levels of the vibrational velocity at the test transducer end which is known from the calibrated output voltage of the vibration pick-up. The vibrational stress at the center of the test transducer S_<max> was calculated from the density ρ, the longitudinal velocity c of the test transducer material, and the vibrational velocity υ at the test transducer end, and it was used to represent the vibrational stress levels of test transducer. The results of 60 minutes continuous measurement showed that any irreversible degradation did not occur at the vibrational stress levels under 2 kg/mm^2. The value of 2kg/mm^2 is less than the previously reported mechanical fatigue limit 3. 85kg/mm^2, therefore, it can be declared that this longitudinal mode transducer can operate without suffering from electrostrictive property degradation and mechanical fatigue at vibrational stress levels under 2kg/mm^2. The surface temperature distribution on the test transducer was also measured by a thermister-type thermometer, and it was made clear that the surface temperature becomes maximum at the center of the length where the vibrational stress becomes maximum and this fact indicates that mechanical vibrational loss appears according to the vibrational stress distribution. Furthermore, it turned out that the surface temperature with each pair of electrodes short circuited(A type resonance operation)is higher than that with each pair of electrodes open circuited(B type resonance operation), and this implies that mechanical vibrational loss at A type resonance is larger than that at B type resonance. It
  • 池田 拓郎
    原稿種別: 本文
    1973 年 29 巻 2 号 p. 108-114
    発行日: 1973/02/01
    公開日: 2017/06/02
    ジャーナル フリー
    In a previous report on the same subject, some correction formulas were proposed to determine the electromechanical constants of piezoelectric vibrator with a small coupling factor or a low Q by the resonance-antiresonance method. The formulas for K=C/C_0, γ=1/Q and δ_m=(ω_m/ω_0)^2-1 are given in terms of w=ω_n/ω_m and r=Y_n/Y_m. However, any influence of the external circuit was not considered there. In the present paper, the effect of the external circuit is included by introducing a resistance R_0 in series with the vibrator, as shown in Fig. 1 and Eqs. (1) and (2). The equivalent circuit of the total impedance can be represented by the circuit 1/Y' shown in Fig. 2 (c), where the components are frequency-dependent and indicated in Eqs. (5)〜(7). The effect of the additive R_0 is taken into account by e in (8) and further approximation of neglecting higher order terms with respect to e is made. Then the circuit components are given by (16). The piezoelectric admittance can be differently expressed by Eqs. (17) and (18), which show that the phase angle φ does not vanish at ω_0. As both R'' and φ depend on ω, the through-the-center approximation requires that the admittance Y_m' or Y_n' goes through the center of the respective circle indicating the motional admittance Y_p' at ω_m or ω_n. These situations are shown in Fig. 3, where the notations are given by (20). A geometrical configuration gives us the relations (22), (23) and (26). Following the equations from (24) to (34) successively, we have the approximate formula (35) for δ_m. Rewriting (28), (36) and eliminating A, the formula for γ is given as (38). Lastly, the formula for K is obtained from (36) and shown in (40). The expressions thus determined involve δ_<mn>, an unobservable quantity. We can use α determined by (42) instead of δ_<mn>α is determined by the measurement. Then we have the approximate formulas for K, γ and δ_m, as collected in (IVα. 1)〜(IVα. 3), when δ_m in (40) and the terms involving F and G in (40) and (38) are ignored. Though the quantity e is not observable, the ratio of the current corresponding to Y_m' to the short-circuit current, or κ in (44), gives the value of e by (45). The introduction of κ brings about another set of formulas (Vα. 1)〜(Vα. 3). The fractional errors of the formulas are examined in a similar way as in the previous paper. The results are shown in Fig. 4, where the errors are plotted against e for several combinations of different M and Q. They give an evidence for the applicability of the approximate formulas IVα and Vα. The proposition of these formulas is the purpose of the present paper.
  • 三浦 甫
    原稿種別: 本文
    1973 年 29 巻 2 号 p. 115-120
    発行日: 1973/02/01
    公開日: 2017/06/02
    ジャーナル フリー
  • 能本 乙彦
    原稿種別: 本文
    1973 年 29 巻 2 号 p. 121-122
    発行日: 1973/02/01
    公開日: 2017/06/02
    ジャーナル フリー
  • 長 真弓
    原稿種別: 本文
    1973 年 29 巻 2 号 p. 123-128
    発行日: 1973/02/01
    公開日: 2017/06/02
    ジャーナル フリー
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