We investigated the improvement of sound insulation of a double-leaf partition using Helmholtz resonators. We proposed a method of predicting the sound reduction index R0 at normal incidence using impedance transfer, under the assumption that the resonators installed in the air cavity between the two leaves were independent components of a wall, similarly to boards and studs. Furthermore, for experimentation, a small sample without studs was used to prevent flanking transmission through them. Theoretical and empirical examinations revealed that installing the resonators in the cavity in the following manner was sufficient to control sound insulation at low frequencies. High sound insulation occurred at the resonance frequency f0 of resonators; the sound insulation decreased at higher and lower frequencies than f0. The sound insulation at f0 depended on the acoustic resistance of resonators. When an air layer existed behind the resonators, other peaks and dips appeared at higher frequencies than f0. Installing both a fibrous absorber and resonators in the cavity was sufficient to recover the decreased performance of sound insulation owing to the installation of resonators.
The road traffic noise in Hanoi is characterized by a large number of motorbikes emitting frequent horn sounds. In order to cross-culturally investigate the effects of horn sounds on annoyance caused by road traffic noise, psychoacoustic experiments were conducted in Hanoi, Vietnam and Kumamoto, Japan. The annoyance caused by 12 types of road traffic noise with and without horn sounds was evaluated using two noise annoyance scales: an 11-point numeric scale and a 5-point verbal scale. The conditions and procedures of the experiments were the same in Hanoi and Kumamoto. The main findings are as follows: (1) the Vietnamese subjects were less affected by horn sounds than were the Japanese subjects; (2) the Japanese subjects were more annoyed by road traffic noise with horn sounds than that without horn sounds; (3) the Japanese subjects were generally more annoyed by road traffic noise than the Vietnamese subjects; and (4) differences between the characteristics of road traffic noise in Japan and Vietnam affected the annoyance of the Japanese subjects.
In binaural reproduction providing spatial sound by means of convolving sound sources and head-related transfer functions (HRTFs), it is important to approximate the listener’s own HRTFs with a high degree of accuracy. HRTF measurement, however, typically requires a great deal of labor, time, and expense. In this paper, a method for estimating such individualized HRTFs that uses principal component analysis (PCA) is introduced. In this method, the orthogonal bases of a set of HRTFs are computed and partially measured HRTFs are interpolated from the weighted sum of the bases. The validity of the method was verified in objective and subjective experiments in which the required approximation accuracy of HRTFs was evaluated.
Nagado-daiko, the most common type of traditional Japanese drum, is known for its unique diaphragm, which is stretched to a relatively high tension compared to other types of drums. The diaphragm is primarily made of cow skin. Once the cow skin is chemically treated, it exhibits Young’s modulus of approximately 3.5×109 Pa, suggesting that the diaphragm should be treated as a stretched plate, or a stiff membrane. This paper reviews the method for obtaining eigenvalues and eigen-frequencies of a membrane with stiffness. Eigenvalues of the 15 lowest modes are given as functions of tension vs. bending stiffness ratios. A double exponential function with four constants is also presented so that eigenvalues (and then resonance frequencies) of the 15 lowest modes can be simply obtained by common calculators. Measured results of a nagado-daiko with a 48 cm diameter show that the effect of stiffness on the spacing of resonance frequencies is negligible in the lowest several modes, contradicting theoretical prediction. A more precise experimental study is necessary to determine the effectiveness of the diaphragm stiffness on the resonance frequencies especially in the mid to high frequency region.
A new microphone, which uses the optical total reflection at the boundary surface between glass and air, is investigated theoretically and experimentally. The critical angle for total reflection changes by the refractive index of air, which depends on the air density. The density changes by the sound pressure. Therefore, the sound pressure is measurable by detecting the intensity of the reflected light from the total reflection area, and it is expected that there is no limitation in the frequency range as the mechanical vibration is not used. The sound pressure sensitivity of the microphone and the effect of surrounding conditions are investigated theoretically. Some experiments are carried out to verify the theoretical investigations, employing a laser diode and a sensor made by cutting off a part of cylindrical glass rod. Experimental results show that the microphone can be used for the measurement of the waveform of high frequency sound though the sensitivity of the microphone is low as expected by the theoretical investigation. The remaining problem is to improve the sensitivity.
Voice activity detection (VAD) plays an important role in speech processing including speech recognition, speech enhancement, and speech coding under noisy environments. We have developed an evaluation framework for VAD under noisy environments, named CENSREC-1-C. We designed this framework for simple isolated utterance detection and hence, this framework consists of noisy continuous digit utterances and evaluation tools for VAD results. We define two evaluation measures, one for frame-level detection performance and the other for utterance-level detection performance. We also provide the evaluation results of a power-based VAD method as a reference.