NOISE%20CANCELLATION%20http://DoctorD.WebHop.Net

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NOISE CANCELLATIONhttp//DoctorD.WebHop.Net

• INTRODUCTION
• TECHNOLOGY
• APPLICATIONS
• DEMONSTRATION
• SUMMARY

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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"

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NOISE CANCELLATIONANTI-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 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 APPROACHESBROAD BAND - ADAPTIVELY
  FILTER THE SIGNAL FROM AN "UPSTREAM" SENSOR
  TO CREATE THE ANTI-NOISE SIGNALSYNCHRONOUS -
  ADAPTIVELY SYNTHESIZE AN ANTI-NOISE SIGNAL
  WITH A-PRIORI KNOWLEDGE OF THE BASIC
  "NOISE CYCLE" RATE
• EFFECTIVE AT LOW FREQUENCIES

"A GOOD SOLUTION USUALLY REQUIRES A COMBINATION
OF PASSIVE AND ACTIVE TECHNIQUES"
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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"
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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
• 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

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Vacuum Muffler

• Application 100 horsepower diesel vacuum.
  Used to load and unload railroad cars (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.

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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.
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CSX MasterVac
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Diesel Engine Muffler

• Application 450 horsepower diesel engine.
  522 in3, 2-stroke Used 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.

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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.
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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)

• 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

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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)

• CHARACTERISTICS
• SELECTIVE
• REDUCE TONAL COMPONENTS TO THE BACKGROUNDNOISE
  LEVEL
• BENEFITS
• SAFETY
• HEARING PROTECTION
• COMFORT
• APPLICATIONS
• EQUIPMENT OPERATORS (IN-CAB)
• GENERAL WORK SITE

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Analog Heaset(Broadband Noise Cancellation)

• 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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Saab 2000 Turboprop

• 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.

OFF
ON
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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

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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