The finite-difference time-domain method, in which longitudinal and shear waves and two types of damping terms are considered, has been proposed as a prediction method for structure-borne sound, particularly architectural acoustics. In this method, it is assumed that both solids and fluids are governed by a unique set of motion equations and viscoelastic constitutive equations. Therefore, the method can be applied to heterogeneous media and vibroacoustic problems by employing averaged material parameters. However, the formulation is limited to isotropic media. Unfortunately wooden frames, which are common building materials, cannot be considered as isotropic media. Herein, a method of formulating heterogeneous orthotropic media is proposed. As an example, the propagation of waves in a wooden block and the radiated sound are calculated. The numerical results of both the time and frequency responses are compared with the measured ones. These investigations show that the calculated data does not correspond to the measured data if the wooden block is assumed to be isotropic. Moreover, the results calculated with orthotropy taken into account agree well with the measured one, but the material parameters must be identified using measured data.
In an earlier paper [T. Otsuru et al., J. Acoust. Soc. Am., 125, 3784–3791 (2009)], the theoretical development and concept of “ensemble averaged” surface normal impedance were summarized by some of the authors using the math–physical model based on the boundary element method (BEM). This paper elaborates further on past discussions of the measuring method of the surface impedance of materials. First, three materials, namely, 50-mm-thick glass wool, 25-mm-thick glass wool, and 10-mm-thick needle felt, were measured in a reverberation room to compare the absorption characteristics measured using sensors of different types. Measured data show good agreement between the sensor types in the absorption coefficients, while some discrepancies are seen in the impedances. Next, the feasibility of our method in terms of sound absorption characteristics was confirmed using a series of measurements in comparison with the impedance tube method. Finally, the effects of sample size and receiver-to-sample distance are presented both in simulation and measurement for investigating the level of utility in various applications. The resulting absorption characteristics are examined to elucidate an appropriate measurement setting and demonstrate the general utility of the method.
This study was designed to evaluate whether or not previously proposed acoustic measures of vowel nasality are applicable for speaker comparison in a forensic context. Three acoustic parameters were selected and analysed for vowels in nasal and oral phonetic environments: the amplitude difference (in dB) between the first formant and the extra peak caused by nasalisation (A1–P1), and the frequencies (in Hz) of the first formant (F1) and extra peak (Fp1). We analysed eighteen monosyllables and six isolated words uttered by fifty male speakers and recorded through a microphone. Recordings were conducted twice for each speaker at a two to five month interval. Between- and within-speaker variations were examined using the F-ratio and by conducting regression analysis between two recording sessions, respectively. Results revealed that Fp1 of front vowels yielded large F-ratio values, which means high speaker-discriminating power and that A1–P1 of the vowels in oral contexts showed within-speaker stability over time.