可流通式次波長聲學結構應用於低頻抗噪入耳式耳塞

Abstract

本文提出了雙空氣流道消聲結構，其尺寸與厚度可以達到次波長，具有寬頻消音的特性來減低噪音和擁有可透氣式的空氣流道來增加空氣流通性，並將其微型化製作出入耳式低頻降噪耳塞，能實現寬頻消音與減緩傳統耳塞所帶來的悶熱感。在本文中，透過分析聲波在管道中的傳遞，以此建立具有聲輻射阻抗、變管效應、熱黏損耗之聲學傳輸線模型，此方法與有限元素 (FEM) 相比，能夠更有效的設計結構幾何參數，而該模型也能夠計算具有穿透損失之吸音率舆無穿透失之共振式吸音板的吸音率，將聲學傳輸線模型與FEM 的結果相比，兩者具有高度一致性，且與實驗量測的結果相當吻合。入耳式低頻降噪耳塞的消聲性能，藉由封閉音場實驗與有限元素模擬相互驗證其插入損失，證明了入耳式耳塞的可行性，並能夠透過聲學傳輸線模型的穿透損失預估其消聲頻段。最終顯示了雙流道結構與微型化入耳式低頻降噪耳塞，具有低頻抗噪通風能力的表現，達到66 %與100 %的10 dB比例頻寬，與68 %的空氣流通率，其結構厚度達到0107 與0.11 。可流通式次波長結構在將來有潛能的應用在大型通風式隔音牆，或是入耳式消聲耳塞。

In this research, a dual-channel sound-insulation structure with subwavelength size and dimension is proposed. It can achieve a broadband sound insulation and matain air circulation due to ventilated an air channel. The structure is farther miniaturized for developing an in-ear low-frequency reducer. Noise-insulation earplugs can achieve broadband noise reduction and reduce the sultry feeling caused by traditional earplugs. In this research, an acoustic transmission line model with acoustic radiation impedance, radiation effect, and thermal viscosity loss is established by analyzing the transmission of sound waves in the duct. Compared with finite element method (FEM), this method can design multiple air-channel structures and optimize their geometry more effectively, and the model can also calculate the sound absorption rate with transmission loss and the sound absorption rate of resonant acoustic panels without transmission loss. The simulation results of both models match well and are in good agreement with the experimental results. The noise cancellation performance of the in-ear low-frequency noise-cancelling earplugs is verified by the closed sound field experiment and the finite element simulations. Finally, the dual-flow channel structure and miniaturized in-ear low-frequency noise-cancelling earplugs have the performance of low-frequency anti-noise ventilation, reaching 66% and 100% of the 10 dB proportional bandwidth, and 68% of the air flow rate, and its structural thickness reaches 0107 and 0.11 . The flow-through subwavelength structure has potential applications in large ventilated soundproof walls or in-ear noise-cancelling earplugs in the future.