Acoustical Science and Technology
Online ISSN : 1347-5177
Print ISSN : 1346-3969
ISSN-L : 0369-4232
Volume 33 , Issue 2
Showing 1-12 articles out of 12 articles from the selected issue
  • Masahiro Toyoda, Hideo Miyazaki, Yoshihide Shiba, Ami Tanaka, Daiji Ta ...
    2012 Volume 33 Issue 2 Pages 77-85
    Published: March 01, 2012
    Released: March 01, 2012
    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.
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  • Nazli Bin Che Din, Toru Otsuru, Reiji Tomiku, Noriko Okamoto, Kusno As ...
    2012 Volume 33 Issue 2 Pages 86-95
    Published: March 01, 2012
    Released: March 01, 2012
    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.
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  • Kanae Amino, Takashi Osanai
    2012 Volume 33 Issue 2 Pages 96-105
    Published: March 01, 2012
    Released: March 01, 2012
    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 (A1P1), 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 A1P1 of the vowels in oral contexts showed within-speaker stability over time.
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