Small highly efficient ultrasonic transducers are in high demand to fabricate compact parametric speakers. We focus on small piezoelectric transducers that can be used for ultrasonic emitters of parametric speakers. Typical small piezoelectric transducers have piezoelectric boards and radial cones. We propose a transducer consisting of a unimorph diaphragm and a flat metal plate. This structure gives two resonant peaks, which are determined by the physical parameters and dimensions of the diaphragms, the flat plate, and their junction structure. Controlling these resonant peaks is one approach to fabricating transducers having the ideal frequency response of the sound pressure for parametric speakers. We devised a design to control these two resonant peaks by adjusting the junction structure of the diaphragm and the flat plate. Using the results of a theoretical analysis, we designed an improved transducer that satisfies the ideal frequency response for parametric speakers.
This study investigated the differences in first-language-based (L1-based) phonetic processing for second language (L2) phonemes among different age groups of adults. A speech-in-speech masking paradigm was utilized to examine the contribution of the L1-based processing. A phoneme identification task in one language was conducted in the presence or absence of an interferer of a masker of the same or a different language. The degree of interference (i.e., the decrease in identification performance) was postulated to increase as the similarity of underlying processes for the target and masker increases. Experiment 1 was conducted to test the effectiveness of the paradigm. As expected, the interference increased as the similarity of underlying processes for the target and masker increased. Experiment 2 examined the perception of English /r/–/l/ and other phonetic contrasts by Japanese listeners in various adult age groups, to examine whether the degree of interference differs depending on the putative degrees of L1-based processing and on age. The results demonstrated such differences and showed that the L1-based processing can be estimated from the decrease in the identification performance. They also suggested that the perception of /r/–/l/ in the initial singleton and initial cluster positions was high L1-based in older adults.
Light propagating through a sound field is affected by variations in the density of the medium caused by sound. Therefore, acoustical measurements using light have been studied. The popular measurement methods use the phase shift of the transmitted light. Because they detect integrated acoustical quantities along the optical path of the detected light, time and effort are required to measure the quantities at a single point. On the other hand, single-point acoustical particle velocity measurement by light scattering has been proposed. Using light scattering enables the measurement of non-integrated quantities because the scattered light includes only the acoustical information at a scattering point. However, a method of non-invasive sound pressure measurement at a single point in a free field has not been established. This paper proposes sound pressure measurement at a scattering point, in which the light scattered by particles in the sound field is observed. The intensity of light scattered in the sound field indicates the sound pressure because the intensity of the scattered light is proportional to the density of scatterers. The theory of light scattering by sounds is formalized, and sound measurement experiments with light scattering are also conducted using water drops and air particles as scatterers.
In Japan, the development of large-scale wind power generation facilities has been promoted since about 2000. Nationwide investigations of the acoustic characteristics of wind turbine noise have been conducted at various wind farms. In this study, to examine the horizontal and vertical radiation characteristics of noise generated from wind turbines, field measurements of noise from a single wind turbine with a rated power of 1.5 MW have been performed. Some receiving points were set circularly around the wind turbine and mounted on a nearby lightning tower. Meteorological and associated wind turbine operational data were collected at 1 s intervals along with corresponding acoustic data. In addition, the sound pressure level distributions at distances of 50 m to 200 m from the wind turbine were investigated. Results revealed distinguishable horizontal directivity of wind turbine noise. The A-weighted sound pressure levels in the crosswind direction are almost 5 dB lower than those in the up- and downwind directions. Furthermore, it has been found that the sound directivity around the wind turbine could be expressed by a simple empirical formula, assuming the wind turbine to be a point source with combined bi- and omnidirectional patterns.
We present a method to simultaneously estimate the cross-sectional area and length of the vocal tract from a speech spectrum. An iterative procedure determines the vocal-tract shape by gradually optimizing the parameter values to produce the target speech spectrum. The vocal-tract shape is updated in each iteration using a sensitivity function representing the change in formant frequency caused by a slight perturbation of the vocal-tract shape. Our method effectively optimizes the vocal-tract shape when combined with the perturbation relationship between the speech spectrum parameters (i.e., cepstral parameters) and formants. The estimation accuracy is examined using area function data for 10 English vowels (Story and Titze, J. Phon., 26, 223–260, 1998). The resulting average errors are 0.36 cm2 for the cross-sectional area and 0.21 cm for the vocal-tract length. This corresponds to a 17.6% and 1.24% error, respectively. The formant frequency recovered from the estimated vocal-tract shape has an error of less than 4% for each of the first four formants. We also determine that the fundamental frequency of the target speech spectrum has an influence on the estimation accuracy.
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