We propose a tunable acoustic absorbing device using a Helmholtz resonator. Timing the resolution frequency of the device to a desired frequency makes it possible to absorb variable sounds. The designed device forms an array of the Helmholtz resonator with a tunable compliance. The experimental results on controlling the resonant frequency of the device will be described. A deep hole array formed by X‐ray lithography is fabricated into the front plate of the device in order to absorb low‐frequency noise. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 83(1): 1–6, 2000

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An adaptive passive noise control system with high-aspect-ratio apertures in a thin perforated plate is presented. An implemented absorber forms an array of Helmholtz resonators which consists of micro-order diameter apertures in a perforated plate and a tunable cavity gap. The simple open-loop control algorithm was employed as a control strategy in order to reduce extra hardware and realize the compact system. The developed adaptive passive noise control system employed high-aspect-ratio apertures in an absorber and adapted for a lower-frequency range without increasing the cavity gap. In the experiment, the compact system could absorb less than 1000 Hz frequency noise with a thin cavity gap, 23 mm. This paper reports the possibilities of a compact adaptive passive noise control system with taking into account of advantages of microstructures based on microelectromechanical systems technology.

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