Acoustical Science and Technology
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Volume 26 , Issue 3
Showing 1-12 articles out of 12 articles from the selected issue
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REVIEW
  • Takao Sawa, Taro Aoki, Ikuo Yamamoto, Satoshi Tsukioka, Hiroshi Yoshid ...
    Volume 26 (2005) Issue 3 Pages 249-257
    Released: May 01, 2005
    JOURNALS FREE ACCESS
    The Japan Agency for Marine-Earth Science and Technology acquired an autonomous underwater vehicle, the URASHIMA, in 2000. It has capacity to cruise for 300 km, and to dive up to 3,500 m depth, and it can approach waypoints correctly using inertial or acoustic navigation during autonomous cruising. Autonomous underwater vehicles are expected to explore environmental problems by measuring various oceanic data. Through sea trials, we have been developing key technologies for the vehicle, such as navigation and power sources. This paper describes the vehicle system and sea trial results.
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PAPERS
  • Hui Ma, Takashi Yano
    Volume 26 (2005) Issue 3 Pages 258-266
    Released: May 01, 2005
    JOURNALS FREE ACCESS
    Disturbance caused by railway and road traffic noises in simulated outdoor (noise levels at LAeq, 6 min of 55, 65 and 75 dB) and indoor (noise levels at LAeq, 6 min of 35, 45 and 55 dB) conditions was investigated in laboratory settings. In each experiment, 30 Japanese and 30 Chinese subjects were requested to perform auditory (listening) and non-auditory (calculation) tasks while each noise was presented for 6 minutes, and then to assess the disturbance caused by the noises using 5-point verbal scales constructed by the ICBEN method. The results showed that though some railway bonus caused by noise masking did exist for auditory task in the outdoor conditions, no railway bonus was found for the other situations. On the contrary, in the indoor conditions, railway noise was evaluated to be a little more disturbing to the activities than road traffic noise by the subjects in most cases. Though the Japanese subjects appeared to be more sensitive to noises than the Chinese subjects, no systematic difference was found between the two subject groups.
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  • Akihiro Kudo, Haruhide Hokari, Shoji Shimada
    Volume 26 (2005) Issue 3 Pages 267-278
    Released: May 01, 2005
    JOURNALS FREE ACCESS
    Many papers have described moving sound image schemes that use loudspeakers or headphones. Since most of these schemes switch the spatial transfer function being used, wave discontinuity occurs at the moment of switching, which degrades the sound quality. While the characteristics of the wave discontinuity depend on the moving sound image scheme used, no paper appears to have considered the relationship between the wave discontinuity and the scheme used. To rectify this omission, this paper examines three approaches: the simple switching approach, the overlap-add approach, and the fade-in·fade-out approach. The sound degradation caused by the wave discontinuity is assessed, and an objective measure, spectrum distortion width, is introduced to quantify the wave discontinuity. Subjective assessments, carried out using Scheffe’s comparison tests, verify that the overlap-add approach with modified hamming window and the fade-in·fade-out approach were better than the other methods.
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  • Masahiko Akiyama, Tomoo Kamakura
    Volume 26 (2005) Issue 3 Pages 279-284
    Released: May 01, 2005
    JOURNALS FREE ACCESS
    Strong focusing of a plane progressive ultrasound wave by a plano-concave lens with a widely opening aperture, which is made of acrylic resin and is submerged in water, is investigated theoretically and experimentally. To eliminate spherical aberration, an elliptic surface lens is introduced. The amplitude of the sound emitted from the lens increases abruptly with propagation toward the focus, then nonlinear harmonic generation in the beam becomes active significantly. The spheroidal beam equation (SBE), which has been previously proposed to be more amendable to the analysis of a highly focused nonlinear beam, is used to predict the first three harmonic components in the beam. To make sure of the effectiveness of the present theory, experiment is executed in water using an elliptic surface lens of eccentricity 0.544 which is attached tightly to a 1.7-MHz planar transducer with a circular aperture of 75-mm in diameter. It has been shown that the experimental data are overall in excellent agreement with the theoretical prediction. Especially, remarkable suppression of side-lobe levels in beam patterns of higher harmonics has been demonstrated successfully.
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