Transcript ppt
NOISE CANCELLATION
http://DoctorD.WebHop.Net
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INTRODUCTION
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TECHNOLOGY
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APPLICATIONS
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DEMONSTRATION
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SUMMARY
J. N. Denenberg Active Noise Cancellation 1
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NOISE CANCELLATION INTRODUCTION
NOISE REDUCTION TECHNIQUES
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MECHANICAL DESIGN
• BALANCE • TRANSIENTS • RESONANCES –
PASSIVE ATTENUATION
• ENERGY ABSORBING MATERIALS • COMPLIANT MOUNTS –
ACTIVE SYSTEMS: NOISE CANCELLATION APPLICATIONS STATUS "NOISE CANCELLATION TECHNOLOGY IS A PRACTICAL SOLUTION TO REAL WORLD PROBLEMS"
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NOISE CANCELLATION ANTI-NOISE
"ACTIVE NOISE CANCELLATION DOES NOT MASK THE NOISE, IT REMOVES A SIGNIFICANT PORTION OF THE NOISE FROM THE ENVIRONMENT"
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NOISE CANCELLATION TECHNOLOGY NOISE
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BROAD BAND
• TURBULENT OR RANDOM NOISE –
NARROW BAND
• TONAL OR HARMONIC NOISE
PASSIVE NOISE CONTROL
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LOCALIZE VIBRATION AND ABSORB ENERGY EFFECTIVE AT HIGH FREQUENCIES ACTIVE CANCELLATION
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TWO BASIC APPROACHES
"A GOOD SOLUTION USUALLY REQUIRES A COMBINATION OF PASSIVE AND ACTIVE TECHNIQUES"
BROAD BAND ADAPTIVELY FILTER THE SIGNAL FROM AN "UPSTREAM" SENSOR TO CREATE THE ANTI-NOISE SIGNAL
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SYNCHRONOUS ADAPTIVELY SYNTHESIZE AN ANTI-NOISE SIGNAL WITH A-PRIORI KNOWLEDGE OF THE BASIC "NOISE CYCLE" RATE EFFECTIVE AT LOW FREQUENCIES
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NOISE CANCELLATION EXAMPLE APPLICATIONS
AT SOURCE
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MUFFLER ALONG A TRANSMISSION PATH
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IN-DUCT FAN NOISE COMPLIANT MOUNT AT THE EAR
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HEADSET
• Broadband • Selective Narrow Band –
QUIET ZONE
• Cabin Quieting
IN-WIRE
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COMMUNICATIONS
"ENGINEERING SOLUTIONS TO NOISE PROBLEMS REQUIRES AS MUCH REAL WORLD APPLICATION KNOWLEDGE AS IT DOES KNOWLEDGE OF ACTIVE NOISE CANCELLATION TECHNOLOGY" J. N. Denenberg Active Noise Cancellation 5
AT SOURCE: MUFFLER (NARROW BAND NOISE CANCELLATION)
IT IS USUALLY BEST TO CANCEL THE NOISE AS CLOSE AS POSSIBLE TO THE SOURCE"
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AT SOURCE: MUFFLER (CONTINUED)
CHARACTERISTICS
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STRAIGHT THROUGH PASSIVE MUFFLER REDUCES BACKGROUND AND HIGH FREQUENCY NOISE
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ACTIVE CANCELLATION AT THE END OF THE EXHAUST GLOBALLY REDUCES TONAL NOISE COMPONENTS TO THE BACKGROUND BENEFITS
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LOW BACK PRESSURE FUEL ECONOMY QUIET SIZE AND WEIGHT APPLICATIONS
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PRIMARY POWER EXHAUST AUXILIARY POWER GENERATORS (EXHAUST NOISE) BULK TRANSFER VACUUM SYSTEMS COMPRESSOR INLET NOISE
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Vacuum Muffler
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Application: 100 horsepower diesel vacuum. Used to load and unload railroad cars (CSX MasterVac –10/1990) Noise Sources
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Vacuum Exhaust: An Active Muffler, along with a straight-through, passive muffler.
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Diesel Exhaust: a better passive muffler.
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Engine Block: Passive housing.
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Vibration: Compliant mounts.
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Condition Original Noise 115 dBA Active System
Vacuum Muffler
(Continued)
91 dBA Back Pressure Note 3 inches of Mercury Blower operates at 15 inches of mercury None 24% Fuel Savings 20% Faster
“The quiet system loads/unloads a rail car 20% faster than the noisy system it replaced.” J. N. Denenberg Active Noise Cancellation 9
CSX MasterVac
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Diesel Engine Muffler
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Application: 450 horsepower diesel engine. 522 in 3 , 2-stroke Used to generate electrical power (Detroit Diesel 6V-92 at 1800 RPM) Noise Sources
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Exhaust: An Active Muffler, along with a straight-through, passive muffler.
Air Intake: Air filter
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Engine Block: Passive housing.
Vibration: Compliant mounts.
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Diesel Muffler Results
(Demonstration Audio) Condition Straight Pipe Noise 123 dBA Back Pressure None Note 2 meters from the exhaust Original Muffler Active System 89 dBA 81 dBA 1.5 inches of Mercury None 12 ft long 2 ft diameter 2% Fuel Savings 20% Smaller
“The Active muffler system is 20% smaller than the conventional passive muffle it replaced.” J. N. Denenberg Active Noise Cancellation 12
Along a Transmission Path
(Broadband Noise Cancellation) "FEED FORWARD CANCELLATION IS THE CLASSICAL APPROACH AND IS OFTEN HIGHLIGHTED IN THE TECHNICAL LITERATURE"
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CONTROLLING VIBRATION
"CONTROLLING VIBRATION NEAR THE SOURCE CAN GREATLY REDUCE ACOUSTICAL NOISE AND REDUCE WEAR"
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COMPLIANT MOUNT
(CONTINUED)
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CHARACTERISTICS
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ROTATING MACHINE FLOATS FREELY AT VIBRATION FREQUENCIES NO VIBRATION ENERGY IS TRANSMITTED THROUGH THE MOUNT FAIL SAFE - THE PASSIVE MOUNT IS STILL THERE IF THE ACTIVE SYSTEM STOPS WORKING BENEFITS
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OPERATOR COMFORT - VIBRATION REDUCED SECONDARY ACOUSTICAL NOISE ELIMINATED REDUCED WEAR APPLICATIONS
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ENGINES AUXILIARY GENERATORS REFRIGERATION UNITS COMPRESSORS
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AT THE EAR: SELECTIVE HEADSET
(NARROW BAND NOISE CANCELLATION) "A SELECTIVE NOISE CANCELING HEADSET CAN IMPROVE WORKER SAFETY BY ENHANCING PERCEPTION OF WARNING SIGNALS"
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AT THE EAR: HEADSET
(CONTINUED)
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CHARACTERISTICS
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SELECTIVE REDUCE TONAL COMPONENTS TO THE BACKGROUND NOISE LEVEL
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BENEFITS
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SAFETY HEARING PROTECTION COMFORT
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APPLICATIONS
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EQUIPMENT OPERATORS (IN-CAB) GENERAL WORK SITE
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Analog Heaset (Broadband Noise Cancellation)
Speakers Residual Microphones
An open-back, analog, noise canceling headset has good low frequency attenuation and passes higher frequencies without attenuation.
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Zone Cancellation
(Interacting Channels) "PLACEMENT OF SPEAKERS AND MICROPHONES REQUIRES CAREFUL ACOUSTICAL ENGINEERING TO PRODUCE A WELL BEHAVED SYSTEM"
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J. N. Denenberg
Saab 2000 Turboprop
OFF ON The SAAB 2000 aircraft (50 passengers) has an ANC system for reducing the noise in the cabin. http://www.ultraquiet.com
This is achieved by measuring the sound with microphones (green) and generating canceling sound waves using speakers (red).
The ANC system has 72 microphones and 36 speakers (a complex multivariable problem).
A key advantage is a dramatic weight savings compared to passive treatments alone.
Sonograms (a graphical representation of sound) left shows sound levels within the aircraft while in flight. Blues and greens represent lower levels, oranges and reds are higher.
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Zone Cancellation
(CONTINUED)
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CHARACTERISTICS
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EFFECTIVE ON TONAL NOISE BELOW 250 HZ SOPHISTICATED ALGORITHM COMPENSATES FOR INTERACTIONS AMONG MICROPHONES AND SPEAKERS
BENEFITS
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COMFORT SAFETY HEARING PROTECTION
APPLICATIONS
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EQUIPMENT CAB (In production turboprop aircraft) SITE OFFICE
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NOISE CANCELLATION SUMMARY
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PRACTICAL SOLUTION TO SELECTED REAL WORLD PROBLEMS SIGNIFICANTLY REDUCES NOISE AND VIBRATION COSTS ARE OFTEN COVERED BY IMPROVED EFFICIENCIES
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SAFETY
• ACCIDENTS • HEARING PROTECTION –
PRODUCTIVITY GAINS
• Better Communications • Better Throughput –
Energy Savings
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