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J. N. Denenberg Active Noise Cancellation 1
NOISE CANCELLATIONhttp://DoctorD.WebHop.Net
• INTRODUCTION
• TECHNOLOGY
• APPLICATIONS
• DEMONSTRATION
• SUMMARY
J. N. Denenberg Active Noise Cancellation 2
NOISE CANCELLATIONINTRODUCTION
• NOISE REDUCTION TECHNIQUES– MECHANICAL DESIGN
• BALANCE• TRANSIENTS• RESONANCES
– PASSIVE ATTENUATION• ENERGY ABSORBING MATERIALS • COMPLIANT MOUNTS
– ACTIVE SYSTEMS: NOISE CANCELLATION• APPLICATIONS• STATUS
"NOISE CANCELLATION TECHNOLOGY IS APRACTICAL SOLUTION TO REAL WORLD PROBLEMS"
J. N. Denenberg Active Noise Cancellation 3
NOISE CANCELLATIONANTI-NOISE
"ACTIVE NOISE CANCELLATION DOES NOT MASK THE NOISE, IT REMOVES A SIGNIFICANT PORTION OF THE NOISE FROM THE
ENVIRONMENT"
J. N. Denenberg Active Noise Cancellation 4
NOISE CANCELLATIONTECHNOLOGY
• NOISE– BROAD BAND
• TURBULENT OR RANDOM NOISE
– NARROW BAND• TONAL OR HARMONIC NOISE
• PASSIVE NOISE CONTROL– LOCALIZE VIBRATION AND ABSORB ENERGY– EFFECTIVE AT HIGH FREQUENCIES
• ACTIVE CANCELLATION– TWO BASIC APPROACHES
BROAD BAND - ADAPTIVELY FILTER THE SIGNAL FROM AN "UPSTREAM" SENSOR TO CREATE
THE ANTI-NOISE SIGNAL
SYNCHRONOUS - ADAPTIVELY SYNTHESIZE ANANTI-NOISE SIGNAL WITH A-PRIORI KNOWLEDGE OF THE BASIC "NOISECYCLE" RATE
– EFFECTIVE AT LOW FREQUENCIES
"A GOOD SOLUTION USUALLY REQUIRES A COMBINATION OF PASSIVE AND ACTIVE TECHNIQUES"
J. N. Denenberg Active Noise Cancellation 5
NOISE CANCELLATIONEXAMPLE APPLICATIONS
• AT SOURCE– MUFFLER
• ALONG A TRANSMISSION PATH– IN-DUCT FAN NOISE
– COMPLIANT MOUNT
• AT THE EAR– HEADSET
• Broadband• Selective Narrow Band
– QUIET ZONE• Cabin Quieting
• IN-WIRE– 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 6
AT SOURCE: MUFFLER(NARROW BAND NOISE
CANCELLATION)
IT IS USUALLY BEST TO CANCEL THE NOISE AS CLOSE AS POSSIBLE TO THE SOURCE"
J. N. Denenberg Active Noise Cancellation 7
AT SOURCE: MUFFLER(CONTINUED)
• CHARACTERISTICS– STRAIGHT THROUGH PASSIVE MUFFLER REDUCES BACKGROUND AND
HIGH FREQUENCY NOISE– ACTIVE CANCELLATION AT THE END OF THE EXHAUST GLOBALLY
REDUCES TONAL NOISE COMPONENTS TO THE BACKGROUND
• BENEFITS– LOW BACK PRESSURE– FUEL ECONOMY– QUIET– SIZE AND WEIGHT
• APPLICATIONS– PRIMARY POWER EXHAUST– AUXILIARY POWER GENERATORS (EXHAUST NOISE)– BULK TRANSFER VACUUM SYSTEMS– COMPRESSOR INLET NOISE
J. N. Denenberg Active Noise Cancellation 8
Vacuum Muffler• Application: 100 horsepower diesel vacuum.
Used to load and unload railroadcars (CSX MasterVac –10/1990)
• Noise Sources
– Vacuum Exhaust: An Active Muffler, along with a straight-through, passive
muffler.
– Diesel Exhaust: a better passive muffler.
– Engine Block: Passive housing.
– Vibration: Compliant mounts.
J. N. Denenberg Active Noise Cancellation 9
Vacuum Muffler (Continued)
Condition Noise Back Pressure Note
Original 115 dBA 3 inches of Mercury Blower operates at 15 inches of mercury
Active System
91 dBA None 24% Fuel Savings20% Faster
“The quiet system loads/unloads a rail car 20% faster than the noisy system it replaced.”
J. N. Denenberg Active Noise Cancellation 11
Diesel Engine Muffler
• Application: 450 horsepower diesel engine. 522 in3, 2-strokeUsed to generate electrical power(Detroit Diesel 6V-92 at 1800 RPM)
• Noise Sources– Exhaust: An Active Muffler, along with a
straight-through, passive muffler.
– Air Intake: Air filter
– Engine Block: Passive housing.
– Vibration: Compliant mounts.
J. N. Denenberg Active Noise Cancellation 12
Diesel Muffler Results(Demonstration Audio)
Condition Noise Back Pressure Note
Straight Pipe
123 dBA None 2 meters from the exhaust
Original Muffler
89 dBA 1.5 inches of Mercury
12 ft long2 ft diameter
Active System
81 dBA None 2% Fuel Savings20% Smaller
“The Active muffler system is 20% smaller than the conventional passive muffle it replaced.”
J. N. Denenberg Active Noise Cancellation 13
Along a Transmission Path
(Broadband Noise Cancellation)
"FEED FORWARD CANCELLATION IS THE CLASSICAL APPROACH AND IS OFTEN HIGHLIGHTED IN THE TECHNICAL LITERATURE"
J. N. Denenberg Active Noise Cancellation 14
CONTROLLING VIBRATION
"CONTROLLING VIBRATION NEAR THE SOURCE CAN GREATLY REDUCE ACOUSTICAL NOISE AND REDUCE WEAR"
J. N. Denenberg Active Noise Cancellation 15
COMPLIANT MOUNT(CONTINUED)
• CHARACTERISTICS– 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– OPERATOR COMFORT - VIBRATION REDUCED
– SECONDARY ACOUSTICAL NOISE ELIMINATED– REDUCED WEAR
• APPLICATIONS– ENGINES – AUXILIARY GENERATORS– REFRIGERATION UNITS– COMPRESSORS
J. N. Denenberg Active Noise Cancellation 16
AT THE EAR: SELECTIVE HEADSET(NARROW BAND NOISE CANCELLATION)
"A SELECTIVE NOISE CANCELING HEADSET CAN IMPROVE WORKER SAFETY BY ENHANCING PERCEPTION OF WARNING SIGNALS"
J. N. Denenberg Active Noise Cancellation 17
AT THE EAR: HEADSET(CONTINUED)
• CHARACTERISTICS– SELECTIVE– REDUCE TONAL COMPONENTS TO THE BACKGROUND
NOISE LEVEL
• BENEFITS– SAFETY– HEARING PROTECTION– COMFORT
• APPLICATIONS– EQUIPMENT OPERATORS (IN-CAB)– GENERAL WORK SITE
J. N. Denenberg Active Noise Cancellation 18
Analog Heaset(Broadband Noise Cancellation)
An open-back, analog, noise canceling headset has good low-
frequency attenuation and passes higher frequencies
without attenuation.Equalizer
Speakers
ResidualMicrophones
J. N. Denenberg Active Noise Cancellation 19
Zone Cancellation(Interacting Channels)
"PLACEMENT OF SPEAKERS AND MICROPHONES REQUIRES CAREFUL
ACOUSTICAL ENGINEERING TO PRODUCE A WELL BEHAVED SYSTEM"
J. N. Denenberg Active Noise Cancellation 20
Saab 2000 TurbopropThe 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.ON
OFF
J. N. Denenberg Active Noise Cancellation 21
Zone Cancellation(CONTINUED)
• CHARACTERISTICS– EFFECTIVE ON TONAL NOISE BELOW 250 HZ– SOPHISTICATED ALGORITHM COMPENSATES FOR
INTERACTIONS AMONG MICROPHONES AND SPEAKERS
• BENEFITS– COMFORT– SAFETY– HEARING PROTECTION
• APPLICATIONS– EQUIPMENT CAB (In production turboprop aircraft)– SITE OFFICE
J. N. Denenberg Active Noise Cancellation 22
NOISE CANCELLATIONSUMMARY
• PRACTICAL SOLUTION TO SELECTED REAL WORLD PROBLEMS
• SIGNIFICANTLY REDUCES NOISE AND VIBRATION• COSTS ARE OFTEN COVERED BY IMPROVED
EFFICIENCIES– SAFETY
• ACCIDENTS
• HEARING PROTECTION
– PRODUCTIVITY GAINS• Better Communications
• Better Throughput
– Energy Savings