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Numerical simulation of transfer and attenuation characteristics of soft-tissue conducted sound originating from vocal tract Otani, Makoto Hirahara, Tatsuya Shimizu, Shota Adachi, Seiji Copyright© 2008 Elsevier Ltd. All rights reserved. Non-audible murmur Finite difference time domain method Soft tissue Spectral decay A non-audible murmur (NAM), a very weak speech sound produced without vocal cord vibration, can be detected by a special NAM microphone attached to the neck, thereby providing a new speech communication tool for functional speech disorders as well as human-to-machine and human-to-human interfaces with inaudible voice input for use with unimpaired. The NAM microphone is a condenser microphone covered with soft-silicone impression material that provides good impedance matching with the soft tissues of the neck. Because higher-frequency components are suppressed severely, however, the NAM detected with this device can be insufficiently clear. To improve NAM clarity, the mechanism of NAM production as well as the transfer characteristics of the NAM in soft neck tissues must be clarified. We have investigated sound propagation from the vocal tract to the neck surface, using a finite difference time domain method and a head model based on magnetic resonance imaging scans. Numerical results show that, compared to air-conducted sound detected in front of a mouth, soft-tissue-conducted sound attenuates 50 dB at 1 kHz, which consists of 30 dB full-range attenuation due to air-to-soft-tissues transmission loss and -10 dB/octave spectral decay due to a propagation loss in soft tissues. The decay agrees well with the spectral characteristics of the measured NAM. (C) 2008 Elsevier Ltd. All rights reserved. ELSEVIER SCI LTD 2009-03 eng journal article AM http://hdl.handle.net/10091/13654 https://soar-ir.repo.nii.ac.jp/records/12452 https://doi.org/10.1016/j.apacoust.2008.05.003 10.1016/j.apacoust.2008.05.003 0003-682X AA00543169 APPLIED ACOUSTICS 70 3 469 472 https://soar-ir.repo.nii.ac.jp/record/12452/files/Numerical_simulation_transfer_attenuation_characteristics.pdf application/pdf 334.7 kB 2015-09-28