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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 - PowerPoint PPT Presentation
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Active Noise ControlActive Noise Controlof Small Axial Cooling Fansof Small Axial Cooling Fans
Brian B. Monson, Scott D. Sommerfeldt, Brian B. Monson, Scott D. Sommerfeldt, Connor DukeConnor Duke
Department of Physics and AstronomyDepartment of Physics and AstronomyBrigham Young UniversityBrigham Young University
147th Meeting of the Acoustical Society of 147th Meeting of the Acoustical Society of AmericaAmerica
New York, New YorkNew York, New YorkMay 25th, 2004May 25th, 2004
OverviewOverview Introduction and BackgroundIntroduction and Background
Experimental ApparatusExperimental Apparatus
Theoretical ModelingTheoretical Modeling
Experimental ResultsExperimental Results
ConclusionsConclusions
Active Noise ControlActive Noise Control Wave Superposition Wave Superposition
(destructive (destructive interference)interference)
ppTT(p) = p(p) = p11(p) + p(p) + p22(p) ≈ 0(p) ≈ 0
Source CouplingSource Coupling(modified radiation (modified radiation
impedance)impedance)
ZZ11 = Z = Z1111 + Z + Z1212
ZZ22 = Z = Z2222 + Z + Z2121
Fan Noise SpectrumFan Noise Spectrum
Harmonically related tones superimposed on a broadband spectrum (tones are dominant)
Fundamental: blade passage frequency (BPF)
Cooling Fan Control Cooling Fan Control SystemSystem
Developed by Gee, Sommerfeldt
Statement of ProblemStatement of Problem
Due to industry constraints, the Due to industry constraints, the previous fan ANC system developed previous fan ANC system developed is not optimized for a real world is not optimized for a real world setting.setting.
Need a compact system to comply Need a compact system to comply with increasing efforts to decrease with increasing efforts to decrease the size of electronic office the size of electronic office equipment (e.g. desktop computers).equipment (e.g. desktop computers).
Cooling Fan Control Cooling Fan Control SystemSystem
Previous SystemPrevious System 80 mm fan80 mm fan 32 mm loudspeakers32 mm loudspeakers 370 Hz BPF370 Hz BPF
ModificationsModifications 60 mm fan60 mm fan 20 mm loudspeakers20 mm loudspeakers 600 Hz BPF600 Hz BPF Increase fan speedIncrease fan speed
On-axis ComparisonOn-axis Comparison 80 mm vs. 60 mm broadband (on axis, non-calibrated, d = 1 m)80 mm vs. 60 mm broadband (on axis, non-calibrated, d = 1 m)
Theoretical ModelingTheoretical ModelingControl loudspeakers
Fan
Theoretical ModelingTheoretical Modeling
Nelson, Curtis, Elliott, BullmoreNelson, Curtis, Elliott, Bullmore
Optimum minimization of radiated power
Global MeasurementsGlobal Measurements
15°
18°
80 mm Fan Results80 mm Fan Results
60 mm Fan Results60 mm Fan Results
Global ComparisonGlobal Comparison
80 mm80 mm 60 mm60 mm IdealIdeal
kdkd MPRMPR kdkd MPRMPR kdkd MPRMPR
BPFBPF 0.40.4 10.1 10.1 dBdB
0.50.5 13.6 13.6 dBdB
0.50.5 ~30 ~30 dBdB
2 x 2 x BPFBPF
0.80.8 16.1 16.1 dBdB
1.01.0 17.6 17.6 dBdB
1.01.0 22 dB22 dB
3 x 3 x BPFBPF
1.21.2 12.8 12.8 dBdB
1.51.5 10.5 10.5 dBdB
1.51.5 14 dB14 dB
Mean-square pressure reduction (MPR)
ConclusionsConclusions Noise reduction does not yet achieve Noise reduction does not yet achieve
theoretical ideal predicted by Nelson theoretical ideal predicted by Nelson et et alal., particularly with BPF., particularly with BPF
Compact system, while remaining less Compact system, while remaining less obtrusive, is able to achieve as good of obtrusive, is able to achieve as good of global noise control performance as global noise control performance as previous system on first three harmonicsprevious system on first three harmonics
Replacement of 80 mm fan with 60 mm Replacement of 80 mm fan with 60 mm fan and ANC system feasiblefan and ANC system feasible
Future WorkFuture Work
Optimize loudspeaker enclosures for Optimize loudspeaker enclosures for better low frequency response better low frequency response (including THD analysis)(including THD analysis)
Examine and compare airflow output Examine and compare airflow output of fan with and without controlof fan with and without control
Analyze control performance with Analyze control performance with increased 60 mm fan speedincreased 60 mm fan speed
AcknowledgementsAcknowledgements
Kent Gee, PSUKent Gee, PSU Benjamin Faber, BYUBenjamin Faber, BYU Lance Locey, BYULance Locey, BYU BYU Acoustics Research GroupBYU Acoustics Research Group
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