http://DoctorD.WebHop.Net
• INTRODUCTION
• TECHNOLOGY
• APPLICATIONS
• DEMONSTRATION
• SUMMARY
J. N. Denenberg Active Noise Cancellation 1

• 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 A
PRACTICAL SOLUTION TO REAL WORLD PROBLEMS"
J. N. Denenberg Active Noise Cancellation 2

NOISE CANCELLATION
ANTI-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 3

NOISE CANCELLATION
TECHNOLOGY
• 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
"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
SYNCHRONOUS ADAPTIVELY SYNTHESIZE AN
ANTI-NOISE SIGNAL WITH A-PRIORI
KNOWLEDGE OF THE BASIC "NOISE
CYCLE" RATE
– EFFECTIVE AT LOW FREQUENCIES
J. N. Denenberg Active Noise Cancellation 4

• 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 5

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 6

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 7

• 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.
J. N. Denenberg Active Noise Cancellation 8

(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 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

J. N. Denenberg Active Noise Cancellation 10

• Application:
450 horsepower diesel engine.
522 in 3 , 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.
J. N. Denenberg Active Noise Cancellation 11

(Demonstration Audio)
Condition Noise Back Pressure
Straight
Pipe
123 dBA 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

(Broadband Noise Cancellation)
"FEED FORWARD CANCELLATION IS THE CLASSICAL APPROACH AND
IS OFTEN HIGHLIGHTED IN THE TECHNICAL LITERATURE"
J. N. Denenberg Active Noise Cancellation 13

"CONTROLLING VIBRATION NEAR THE SOURCE CAN GREATLY
REDUCE ACOUSTICAL NOISE AND REDUCE WEAR"
J. N. Denenberg Active Noise Cancellation 14

(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 15

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 16

(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 17

(Broadband Noise Cancellation)
Speakers
Residual
Microphones
An open-back, analog, noise canceling headset has good lowfrequency attenuation and passes higher frequencies without attenuation.
J. N. Denenberg Active Noise Cancellation
Equalizer
18

(Interacting Channels)
"PLACEMENT OF SPEAKERS
AND MICROPHONES
REQUIRES CAREFUL
ACOUSTICAL ENGINEERING
TO PRODUCE A WELL
BEHAVED SYSTEM"
J. N. Denenberg Active Noise Cancellation 19

J. N. Denenberg
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.
Active Noise Cancellation 20

(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 21

• 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
J. N. Denenberg Active Noise Cancellation 22