勞工在工作環境中若長久暴露於高噪音之環境下，會對聽力健康造成嚴重的危害，政府已有法令明文規定防音防護具之使用場合及必要性，以避免勞工遭受外界噪音傷害。
本研究以有限元素結構模型與間接邊界元素流體模型耦合的分析方式探討耳罩的聲振耦合現象，模擬分析得到聲音穿透耳罩後，在耳罩內部之聲壓分佈。初步實驗結果顯示耳罩在1000Hz以上的隔音效果較為優異，可達30dB以上，而在1000Hz以下之隔音效果則較差，在1/1八音程中心頻率125Hz的插入損失不足3dB，在250Hz約7至10dB，500Hz約22至25dB，因此本研究的目標為設法改善耳罩在1000Hz頻帶以下(包含1000Hz)的隔音效果。
本研究提出了數種肋條強化結構，提升耳罩的剛性以改善隔音效果。模擬結果顯示，除了提高整體結構之剛性之外還須抑制結構的振動量，才能有效地增加隔音效果；模擬結果以十字環圈型肋條的隔音效果最佳，與耳罩原始結構相比較，在125Hz時增加10.7dB，250Hz時增加9.8dB，500Hz時增加8.8dB，1000Hz時增加11.4dB。在環圈型肋條的探討中，可以得知增加環圈肋條寬度及厚度對隔音效果能進一步提升，與耳罩原始結構相比較，十字環圈型肋條(寬度及厚度2cm)在125Hz時增加15.6dB，250Hz時增加14.4dB，500Hz時增加13dB，1000Hz時增加20.5dB。

Exposed to the high-level noise in working environments for extended time would cause serious damage to workers' hearing. The government has legislated for the occasions of using hearing protection devices(HPD) in order to protect labors from being injured by external noise.
This thesis studied the vibro-acoustic phenomenon of an earmuff by combining the finite element structure model and the indirect boundary element acoustic model. Simulation results showed the distribution of sound pressure inside the earmuff. Results of our experiments revealed that the sound insulation of an earmuff is only good above 1000Hz, which could be over 30dB. The insertion loss in the 125 Hz 1/1 octave frequency band is less than 3dB, 7 to 10dB at 250Hz, and about 22 to 25dB at 500Hz. Therefore, the main goal of this research is to improve the sound insulation of an earmuff below 1000Hz.
This research proposed several rib-strengthened structures trying to improve the sound insulation of an earmuff by increasing its stiffness. Results from simulation showed that in addition to increasing the overall structural stiffness, vibration displacements in influential regions have to be reduced to effectively improve the sound insulation. Among the cases that we investigated, the cross-and-ring type rib-strengthened earmuff offered the best insulation effect. Compared with the original earmuff, insertion loss was shown to be increased by 10.7dB at 125Hz, 9.8dB at 250Hz, 8.8dB at 500Hz, and 11.4dB at 1000Hz. When the width and thickness of the stiffened ring was increased from 1 cm to 2 cm, the insertion loss was further increased by about 5 dB at each frequency band from 125Hz to 1000Hz.

[1] 張錦松、韓光榮、張錦輝，噪音振動控制，高立圖書有限公司，2004。
[2] Berger, E. H., “Active Noise Reduction(ANR) in Hearing Protection: Does it Make Sense for Industrial Application,” 27th Conference of the National Hearing Conservation Association, Dallas, February, 2002.
[3] Lee, C. M., Royster, L. H., and Ciskowski, R. D., “Formulation for FE and BE Coupled Problem and its Application to the Earmuff-earcanal System,” Engineering Analysis with Boundary Elements, Vol. 16, No. 4, pp. 305-315, 1995.
[4] Vergara, F., Gerges, S. N., and Birch, R. S., “Numerical and Experimental Study of Impulsive Sound Attenuation of an Earmuff,” Shock and Vibration, Vol. 9, No. 4, pp. 245-251, 2002.
[5] Birch, R. S., Gerges, S. N., and Vergara, F., “Design of a Pulse Generator and Shock Tube for Measuring Hearing Protector Attenuation of High-amplitude Impulsive Noise,” Applied Acoustics, Vol. 64, No. 4, pp. 269-286, 2003.
[6] Paakkonen, R., “Effects of Cup, Cushion, Band Force, Foam Lining and Various Design Parameters on the Attenuation of Earmuffs,” Noise Control Engineering Journal, Vol. 38, No. 2, pp. 59-65, 1992.
[7] Schroeter, J., “The use of Acoustical Test Fixture for the Measurement of Hearing Protector Attenuation. Part I: Review of Previous Work and the Design of an Improved Test Fixture,” Journal of the Acoustical Society of America, Vol. 79, No. 4, pp. 1065-1081, 1986.
[8] 黃宗正，防音防護具舒適性能評估研究，元智大學機械工程研究所碩士論文，2002。
[9] 陳興、周永樂、陳秋蓉，耳罩插入損失測試標準，中華民國音響學會第七屆學術研討會論文集，pp. 280-288，1994。
[10] 白明憲，聲學理論與應用，全華科技圖書股份有限公司，2001。
[11] 賴育良、林啟豪、謝忠祐，ANSYS電腦輔助工程分析，儒林書局，1997。
[12] LMS Inc. Company, SYSNOISE Ver 5.5 User’s Manual, 2000.
[13] 康淵、陳信吉，ANSYS入門，全華科技圖書股份有限公司，2002。
[14] Callister, W. D., Materials Science and Engineering An Introduction, John Wiley & Sons, New York, 1997.
[15] 施世豪，吸音材料阻抗特性與聲場影響，逢甲大學機械工程研究所碩士論文，2002。