Title page for ETD etd-11152002-103619


Type of Document Master's Thesis
Author Charpentier, Arnaud
Author's Email Address acharpen@vt.edu
URN etd-11152002-103619
Title Active Control Of Noise Radiated From Personal Computers
Degree Master of Science
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Fuller, Christopher R. Committee Chair
Johnson, Martin E. Committee Member
Wicks, Alfred L. Committee Member
Keywords
  • zone of quiet
  • digital signal processing
  • noise cancellation in short duct
  • adaptive feedforward digital controller
  • fan noise
  • feedforward adaptive control
  • lined duct
  • coherence
  • causality
Date of Defense 2002-11-11
Availability unrestricted
Abstract
As an indirect consequence of increased heat cooling requirements, personal computers (PC) have become noisier due to the increased use of fans. Hard disk drives also contribute to the annoying noise radiated by personal computers, creating a need for the control of computer noise.

Due to size constraints, the implementation of passive noise control techniques in PC is difficult. Alternatively, active noise control (ANC) may provide a compact solution to the noise problems discussed above, which is the subject of this work.

First, the computer noise sources were characterized. The structure-borne path was altered passively through the decoupling of the vibrating sources from the chassis. Global noise control strategy was then investigated with a hybrid passive/active noise control technique based on folded lined ducts, integrating microphones and speakers, that were added to the PC air inlet and outlet. While the ducts were effective above 1000Hz, the use of a MIMO adaptive feedforward digital controller lead to significant noise reduction at the ducts outlets below 1000Hz. However, global performance was limited due to important airborne flanking paths. Finally, the same type of controller was used to create a zone of quiet around the PC user head location. It was implemented using multimedia speakers and microphones, while the computer was placed in a semi-reverberant environment. A large zone of quiet surrounding the head was created at low frequencies (250Hz), and its size would reduce with increasing frequency (up to 1000Hz).

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