J. N. DenenbergActive Noise Cancellation1 NOISE CANCELLATION INTRODUCTION TECHNOLOGY APPLICATIONS DEMONSTRATION SUMMARY

J. N. DenenbergActive Noise Cancellation2 NOISE CANCELLATION INTRODUCTION 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. DenenbergActive Noise Cancellation3 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. DenenbergActive Noise Cancellation4 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 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 "A GOOD SOLUTION USUALLY REQUIRES A COMBINATION OF PASSIVE AND ACTIVE TECHNIQUES"

J. N. DenenbergActive Noise Cancellation5 NOISE CANCELLATION EXAMPLE 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. DenenbergActive Noise Cancellation6 AT SOURCE: MUFFLER (NARROW BAND NOISE CANCELLATION) IT IS USUALLY BEST TO CANCEL THE NOISE AS CLOSE AS POSSIBLE TO THE SOURCE"

J. N. DenenbergActive Noise Cancellation7 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. DenenbergActive Noise Cancellation8 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.

J. N. DenenbergActive Noise Cancellation9 Vacuum Muffler (Continued) ConditionNoiseBack PressureNote Original 115 dBA3 inches of MercuryBlower operates at 15 inches of mercury Active System 91 dBANone24% Fuel Savings 20% Faster “The quiet system loads/unloads a rail car 20% faster than the noisy system it replaced.”

J. N. DenenbergActive Noise Cancellation10 CSX MasterVac

J. N. DenenbergActive Noise Cancellation11 Diesel Engine Muffler 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. DenenbergActive Noise Cancellation12 Diesel Muffler Results (Demonstration Audio) ConditionNoiseBack PressureNote Straight Pipe 123 dBANone2 meters from the exhaust Original Muffler 89 dBA1.5 inches of Mercury 12 ft long 2 ft diameter Active System 81 dBANone2% Fuel Savings 20% Smaller “The Active muffler system is 20% smaller than the conventional passive muffle it replaced.”

J. N. DenenbergActive Noise Cancellation13 Along a Transmission Path (Broadband Noise Cancellation) "FEED FORWARD CANCELLATION IS THE CLASSICAL APPROACH AND IS OFTEN HIGHLIGHTED IN THE TECHNICAL LITERATURE"

J. N. DenenbergActive Noise Cancellation14 CONTROLLING VIBRATION "CONTROLLING VIBRATION NEAR THE SOURCE CAN GREATLY REDUCE ACOUSTICAL NOISE AND REDUCE WEAR"

J. N. DenenbergActive Noise Cancellation15 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. DenenbergActive Noise Cancellation16 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. DenenbergActive Noise Cancellation17 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. DenenbergActive Noise Cancellation18 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 Residual Microphones

J. N. DenenbergActive Noise Cancellation19 Zone Cancellation (Interacting Channels) "PLACEMENT OF SPEAKERS AND MICROPHONES REQUIRES CAREFUL ACOUSTICAL ENGINEERING TO PRODUCE A WELL BEHAVED SYSTEM"

J. N. DenenbergActive Noise Cancellation20 Saab 2000 Turboprop The SAAB 2000 aircraft (50 passengers) has an ANC system for reducing the noise in the cabin. 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. DenenbergActive Noise Cancellation21 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. DenenbergActive Noise Cancellation22 NOISE CANCELLATION SUMMARY 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