| 摘要 |
<p>PROBLEM TO BE SOLVED: To solve a problem in eliminating noise depending on a certain frequency of a primary sound, wherein a zone where no noise eliminating effect acts is generated in a frequency of integral multiple. SOLUTION: The propagating primary sound is obtained by a sensor 6a, and in accordance with a peak frequency, dimensions of expansion chambers 2 and 3 are changed by a driving device 12a thereby eliminating its peak sound. A secondary sound after noise eliminating is obtained by a sensor 6b, and the peak frequency remaining in the secondary sound is detected. An insertion pipe length enough for effectively eliminating the detected peak frequency is calculated by a control device 9, and the insertion pipe length is changed by a driving device 12b, thereby also eliminating the peak sound of the secondary sound.</p> |
