A flat diaphragm full-range loudspeaker utilizing a piezoelectric polymer is described. This loudspeaker is characterized by an excellently simple constitution and multiresonance response characteristics. Since the fundamental resonant frequency of a loudspeaker should be as low as possible, it is convenient to utilize the flexural vibration of a bimorph diaphragm. The input-output relation of a bimorph diaphragm radiator in a multi-resonance frequency region is studied theoretically, and the formula for estimating output sound pressure level for the resonant peak is given. This is also examined experimentally.

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The sound reflection coefficient of a given material, which is measured from a sufficiently large plane of it for spherical wave incidence, has been used previously to predict the first reflection for plane, convex or concave, finite size panels covered with that material. The first reflection of such a panel can be treated as two separate waves. One is the wave from the specular reflection point and the other is a boundary wave comprised of components from the lined point sources at each edge. Here, multiple reflections between two plane panels covered with materials having reflection coefficients that may be different are approximately calculated from such separate waves as in the same treatment of rigid plane panels.

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This paper describes the complexity of forced vibration of a flexible string, on the basis of the concept analogous to entropy, popular in thermodynamics and communication theory, which the authors have introduced for evaluating the complexity of a reverberant field in a recent paper. The entropy of string vibration is defined in terms of energy contribution of each normal mode in which the vibration is formulated, and is discussed in connection with the frequency components and location of a driving force and with transient characteristics by unit impulsive force. As a result, it is found that the entropy increases with an increase in frequency band width of the force and approaches infinity, and that although the driving point varies the entropy according to the band width, it tends to be raised when random excitation. Moreover, in the transient response of the string, the entropy is shown to decrease with time after the excitation. Thus, the entropy employed here well represents the degree of energy distribution to each mode, and within this meaning, seems to be fit for a measure of complexity of the string vibration.

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This study investigates and acoustically defines some of the perceptual parameters which characterize alaryngeal voice quality. Twenty voice samples of vowel /e/ were recorded from 16 alaryngeal and four normal speakers, and were paired, randomized and presented to 20 listeners with normal hearing. The listeners rated the dissimilarities of all combinations of the voices, and these dissimilarities were analyzed by a nonmetric multidimensional scaling method called SMACOF. Five acoustical measures and 21 psychoacoustical ratings were made for each vowel, and these provided the interpretation for the SMACOF solution. The results indicate that at least two dimensions are necessary to describe the alaryngeal voice quality. One is connected with the listeners' preferences for the voices and differentiates the alaryngeal voices from the normal ones. This dimension correlates with the fundamental frequency and the relative spectral level of the high frequency components. Another dimension indicates the abnormalities peculiar to the voices produced with artificial larynges and differentiates them from the normal and esophageal voices. It correlates positively with periodicity in the excitation signal waveform and negatively with aperiodicity in the pitch or in the amplitude. These results suggest some direction toward the enhancement of the alaryngeal voice quality.

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Nonlinear response of acoustic materials to a large amplitude sound depends upon the incident waveform itself. For this reason, we intend to control the radiated waveform of finite amplitude in free space. In order to control the radiated waveform, the waveform control in a pipe was performed by the use of the loudspeaker driven by the computed waveform, and generated wave was radiated from an exponential horn connected to the end of the pipe. However, the observed waveform in free space was different slightly from expected one. As the result of the simulation for the sound transmission through the exponential horn, it became clear that the reflection of the mouth of the horn affected the radiated waveform in free space. Therefore, the waveform control in the pipe was performed by taking account of the effect of the horn and then the result obtained agreed approximately with the waveform expected.

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