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Active Noise Control of Small Axial Cooling Fans

Active Noise Control of Small Axial Cooling Fans. Brian B. Monson, Scott D. Sommerfeldt, Connor Duke Department of Physics and Astronomy Brigham Young University 147th Meeting of the Acoustical Society of America New York, New York May 25th, 2004. Overview. Introduction and Background

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Active Noise Control of Small Axial Cooling Fans

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  1. Active Noise Controlof Small Axial Cooling Fans Brian B. Monson, Scott D. Sommerfeldt, Connor Duke Department of Physics and Astronomy Brigham Young University 147th Meeting of the Acoustical Society of America New York, New York May 25th, 2004

  2. Overview • Introduction and Background • Experimental Apparatus • Theoretical Modeling • Experimental Results • Conclusions

  3. Active Noise Control • Wave Superposition (destructive interference) pT(p) = p1(p) + p2(p) ≈ 0 • Source Coupling (modified radiation impedance) Z1 = Z11 + Z12 Z2 = Z22 + Z21

  4. Fan Noise Spectrum • Harmonically related tones superimposed on a broadband spectrum (tones are dominant) • Fundamental: blade passage frequency (BPF)

  5. Cooling Fan Control System Developed by Gee, Sommerfeldt

  6. Statement of Problem Due to industry constraints, the previous fan ANC system developed is not optimized for a real world setting. Need a compact system to comply with increasing efforts to decrease the size of electronic office equipment (e.g. desktop computers).

  7. Cooling Fan Control System • Previous System • 80 mm fan • 32 mm loudspeakers • 370 Hz BPF • Modifications • 60 mm fan • 20 mm loudspeakers • 600 Hz BPF • Increase fan speed

  8. On-axis Comparison • 80 mm vs. 60 mm broadband (on axis, non-calibrated, d = 1 m)

  9. Control loudspeakers Fan Theoretical Modeling

  10. Theoretical Modeling Optimum minimization of radiated power Nelson, Curtis, Elliott, Bullmore

  11. 15° 18° Global Measurements

  12. 80 mm Fan Results

  13. 60 mm Fan Results

  14. Global Comparison Mean-square pressure reduction (MPR)

  15. Conclusions • Noise reduction does not yet achieve theoretical ideal predicted by Nelson et al., particularly with BPF • Compact system, while remaining less obtrusive, is able to achieve as good of global noise control performance as previous system on first three harmonics • Replacement of 80 mm fan with 60 mm fan and ANC system feasible

  16. Future Work • Optimize loudspeaker enclosures for better low frequency response (including THD analysis) • Examine and compare airflow output of fan with and without control • Analyze control performance with increased 60 mm fan speed

  17. Acknowledgements • Kent Gee, PSU • Benjamin Faber, BYU • Lance Locey, BYU • BYU Acoustics Research Group

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