著者

武藤 大輔 高野 靖

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 C編 (ISSN:03875024)

巻号頁・発行日

vol.74, no.746, pp.2495-2503, 2008-10-25 (Released:2011-03-04)

参考文献数

5

被引用文献数

3 3

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The dependence of transmission loss (TL) of a double-wall structure on the characteristics of the gases between the walls was investigated. The relationship between acoustic impedance, acoustic velocity, and TL was calculated by using the transfer matrix method. The results indicated that characteristics of the internal gases have two effects on TL. One is a change in the double-wall effect, and the other is a change in the reflection coefficient. Gases that have slower acoustic velocities or lower acoustic impedance than air increase the double-wall effect. Gases that have faster acoustic velocities increase the reflection coefficient. The calculated results for TL with air, helium, and carbon dioxide agreed well with experimental measurements. Finally, The rating of sound insulation (Rw) defined by JIS A1419-1 (ISO-717) was introduced, and the relationship between Rw and the characteristics of the gases between walls was investigated. The results indicate that gas with a low molecular weight and large ratio of specific heat is more effective to increase the TL.

著者

武藤 大輔 高野 靖 山口 誉夫

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.855, pp.17-00106-17-00106, 2017 (Released:2017-11-25)

参考文献数

11

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To increase the noise proof performance of a cover with aperture excited by diffuse acoustic fields from the outside, it is a problem to prevent the occurrence of the inner acoustic mode at the lower frequencies. Authors had suggested the feed forward active noise control (ANC) for the acoustic field inside the cover. Diffuse acoustic field excitation experiment using reverberant room has been examined to comprehend acoustic characteristics inside the cover. The results show that the inner cover field is in the state of locally coherent at the frequencies of inner acoustic mode, so that it is good environment for the active noise control. Then, a calculation with two-dimensional finite difference time domain (FDTD) method has been done to examine the feasibility of feed forward ANC. The results show that it is possible to realize ANC for the acoustic field inside the cover by proper design of control filter. Finally, experimental measurement of diffuse acoustic field excitation in the reverberant room has been done again to examine the ANC with the design method mentioned above. The results show that feed forward ANC can reduce noise level by 5dB at the peak frequency caused by the inner acoustic mode. Furthermore, the inner acoustic pressure distribution is also reduced uniformly at the frequency. Therefore, it is concluded that it is possible to realize feed forward active noise control for the acoustic field inside the cover with aperture excited by diffuse acoustic fields from the outside, even if the excitation is random or the causality of I/O is not satisfied.