Proceeding from the eigenvalue equation of the normal mode in homogeneous shallow water, we derive several formulae calculating the mode attenuation and group velocity, and compare their accuracy by means of numerical...Proceeding from the eigenvalue equation of the normal mode in homogeneous shallow water, we derive several formulae calculating the mode attenuation and group velocity, and compare their accuracy by means of numerical results. The paper especially discusses the attenuation and the group velocity of critical mode in a Pekeris channel and shows that in general, the attenuation and the group velocity of the critical mode respectively are less than the absorption and the sound speed in the bot -torn . Therefore, the Kornhauser, Raney, Weston Tindle ' s conclusions are modified that the attenuation and the group velocity of the critical mode are exactly equal to the absorption and the sound speed in the bottom, respectively.展开更多
Quantitative estimation of sound transmission attenuation by different middle-ear protecting mechanisms was made with the use of a computer-based CM-cogram analyzing method (FFT of cochlear output in response to white...Quantitative estimation of sound transmission attenuation by different middle-ear protecting mechanisms was made with the use of a computer-based CM-cogram analyzing method (FFT of cochlear output in response to white noise) and other audiometric means. Strong reflex contraction of the middle-ear muscles in guinea pigs may cause a 5- 20 dB transmission attenuation in different frequency ranges. For impulse noise exposure, the presence of an effective reflex at the lashing of every impulse may reduce the post - exposure hearing threshold shift in 15 dB on an average.Increasing tension of the tympanic membrane by applying pressure to the ear- canal is also eflicacious.especially for frequencies below 500 Hz where attenuation of more than 10dB may result at a pressure difference of about 200mm H2O between the two sides of the membrane. Simulated opening of the eustachian tube helps only very insignificantly, with attenuation less than 5 dB. Destruction of the middle-ear structures ( drum perforation, ossicular disruption etc .) and fluid accumulation inside the tympanic cavity may buffer acoustic trauma to the cochlea to different extent depending on the amount of transmission attenuation.展开更多
文摘Proceeding from the eigenvalue equation of the normal mode in homogeneous shallow water, we derive several formulae calculating the mode attenuation and group velocity, and compare their accuracy by means of numerical results. The paper especially discusses the attenuation and the group velocity of critical mode in a Pekeris channel and shows that in general, the attenuation and the group velocity of the critical mode respectively are less than the absorption and the sound speed in the bot -torn . Therefore, the Kornhauser, Raney, Weston Tindle ' s conclusions are modified that the attenuation and the group velocity of the critical mode are exactly equal to the absorption and the sound speed in the bottom, respectively.
文摘Quantitative estimation of sound transmission attenuation by different middle-ear protecting mechanisms was made with the use of a computer-based CM-cogram analyzing method (FFT of cochlear output in response to white noise) and other audiometric means. Strong reflex contraction of the middle-ear muscles in guinea pigs may cause a 5- 20 dB transmission attenuation in different frequency ranges. For impulse noise exposure, the presence of an effective reflex at the lashing of every impulse may reduce the post - exposure hearing threshold shift in 15 dB on an average.Increasing tension of the tympanic membrane by applying pressure to the ear- canal is also eflicacious.especially for frequencies below 500 Hz where attenuation of more than 10dB may result at a pressure difference of about 200mm H2O between the two sides of the membrane. Simulated opening of the eustachian tube helps only very insignificantly, with attenuation less than 5 dB. Destruction of the middle-ear structures ( drum perforation, ossicular disruption etc .) and fluid accumulation inside the tympanic cavity may buffer acoustic trauma to the cochlea to different extent depending on the amount of transmission attenuation.
