A new method of designing a miniature condenser microphone for broadcasting is described. In order to make a superior T. V. broadcasting microphone, the sound quality and visual quality must be designed compatibly. In this paper, a designing method considering not only the sound quality but also the visual quality is described. At first, the outer diameter of microphone is determined from the visual quality. The result indicates that the diameter of lapel or tie microphone is desirable to be less than 8mm. For the purpose to realizing this requirement, some problems are discussed. The principal problem is to reduce the damping resistance so as to match the mechanical impedance level of a small and light diaphragm without decreasing the electrostatic capacitance that has its minimum value required from the condition of electrical circuit, especially the ratio of signal to noise(Fig. 2). In this paper, a new structure of back electrode that is composed of a porous material is proposed. From some experiments about the electrical and acoustical characteristics, the porous metal which has the crevices of 40μm mean diameter is suitable. Using this material, a miniature condenser microphone(Fig. 23)is manufactured trially. The sensitivity is -47dB(re 1V/μbar)and the frequency characteristics is shown in Fig. 22.
In pitch perception of complex tones, two kinds of pitch are recognized. Namely, in the lower pitch region the temporal information can be as a dominant cue in pitch perception, while the spectral one is dominant in the higher pitch region. Some different values, however, are reported by certain authors as the upper frequency limit of periodicity pitch. They are considered to be divided into two groups, i. e. about 800Hz and 200Hz. It is not expected that the transition from the periodicity pitch to the place pitch occurs abruptly. There may exist the frequency region where the periodicity pitch coexists with the place pitch. Therefore, the frequency region where the temporal information is a dominant cue in pitch perception may be lower than the upper frequency limit of periodicity picth. In order to investigate this region, we determined the pitch of the following stimuli;(a)a pulse train in which every second pulse is shifted 3 to 30% from its regular place along the time axis, (b)a pulse train in which the intensity of every second pulse is attenuated from 2 to 10dB, and (c)a pulse train in which a jitter is imposed on the time of appearance of every second pulse. The fundamental frequency of these series is a half of the pulse-rate. The results obtained are as follows:(1)As a relative displacement of every second pulse increases, the proportion of pulse-rate match decreases(Fig. 3)and instead the proportion of fundamental frequency match increases. (2)As a relative intensity of every second pulse decreases, the proportion of pulse-rate match decreases(Fig. 7). (3)As a relative temporal jitter of every second pulse increases, the proportion of pulse-rate match decreases(Fig. 9). (4)Along with an increase in pulse-rate, the pitch mode changes from pulse-rate match to fundamental frequency match. Up to about 150pps, in general, the pulse-rate match is dominant, where as the fundamental frequency match is dominant above 200 or 250pps for stimulus(a)and stimulus(b), and above 400pps for stimulus(c). Judging from the histograms of pitch matching(Fig. 4)and responses of basilar membrane model(Fig. 10 and 11)to stimuli used, it seems that the pitch is perceived on the basis of the temporal cue in the region of pulse-rate match and on the basis of the spectral cue in the region of fundamental frequency match. From these results, it is considered that the temporal cue is dominant in pitch perception up to about 200pps.
The utility of a plain tuning fork(Fig. 1)is experimentally examined in this paper. The optimum position and dimensions of a piezoelectric ceramics which minimize the capacitance ratio γ of a plain tuning fork are investigated(Figs. 2, 3, 4, 5)and equivalent constants of the plain tuning fork are measured under such conditions(Figs. 6, 7, 8 and Table 1). Resonance frequency is 28〜43% higher than that of a conventional tuning fork, and the value of γ is about 25% larger but Q is about 25% higher than those of a conventional tuning fork. Moreover, spurious characteristics(Figs. 9, 10, 11), influence of additional mass(Figs. 12, 13), supporting device(Figs. 14, 15, 16)and attenuation characteristic of a differential type filter composed of two plain tuning forks(Figs. 17, 18 and Table 2, 3)are discussed in detail. As a result, it is confirmed that the plain tuning fork is favorable for practical use in the low frequency region.
In the application of longitudinal vibration, a conventionally vibrational system is almost of one-dimensional construction such as a solid horn. In this case high vibrational energy could not be available because of the radial coupling of the vibration. The authors believe that it may be more convenient if ultrasonic energy can be transmitted from the driver to any directions, and can be concentrated additively by parallel operation of drivers, and further can be divided among plural loads from single vibrational source. From this point of view, the authors have devised the resonator with directional converters of three basic types, the two of which(called L-L and L-L-L Types converters)were reported previously. This paper deals with the directional converter(called R-L type converter)in which one radial vibration disk and one longitudinal vibration bar are mutually connected three-dimensionally at their node part of vibration(as shown in Fig. 4). In this type, the stress or strain of longitudinal or radial vibration is maximum at the coupling, and it has two fundamental resonant frequencies(as shown in Table1), one being the in-phase-mode, the other the anti-phase-mode(as shown in Fig. 3). As in the case of the converter, each single disk as well as single bar has two fundamental resonant frequencies of the in-phase-mode and anti-phase-mode(as shown in Table2 and 3). In all cases, the resonant frequencies of the in-phase-mode are higher than that of the anti-phase-mode. The authors have analyzed the converter by making some assumptions and by defining equivalent elastic modula of coupling part to each axis(as shown in Table4, equations(3〜6))from these vibrational characteristics and obtained the equations(10〜14)to design, and also we designed, produced and measured the new converter. The results of the measurements agreed within two percents with the designed resonant frequency(as shown in Fig. 10, 11), with the calculated value of viblational velocity ratio(as shown in Fig. 13, 14), and with the calculated distribution curves of vibrational velocity along each axis(as shown in Fig. 12). From this result, it was found that these equations are satisfactory to indicate these vibrational characteristics of the converters.