integrated acoustics laboratory active noise reduction hearing protectors: 50 years of development...

Integrated Acoustics Laboratory

Active noise reduction hearing protectors: 50 years of development

Kenneth A. Cunefare

Associate Professor

Professor in Charge, Integrated Acoustics Laboratory

George W. Woodruff School of Mechanical Engineering


• How we got here• Technology challenges of the past

• Technology challenges of the present

• Olson & May 1953, 1956

• Meeker 1958, 1959

• A host of others

Outline


Olson & May, Electronic sound absorber, JASA 25(6), 1130-1136, 1953


Precursor

• 48th ASA, Austin, 1955 (15 page program!)


Precursor

• 51st ASA meeting, MIT, 1956 (49 pages)


Olson, Electronic control of noise, vibration, and reverberation, JASA 28(5),

966-972, 1956


Meeker, “Active ear defender systems: component considerations and theory,” WADC TR 57-368, 1958

• Cast of characters• Project directors

• Hawley & Dolch through 1955

• Touger and Meeker 55-58

• Participants• Simshauser

• Balakrishnan

• Olson & Woll consultants

• Air Force: Lt. David T. Blackstock & Charles Nixon

• Target 25 dB from 50 to 1000 cps


Meeker 1958

• Feedback, open-loop/feed-forward, and local control


Meeker 1958

• Forward-acting system (System I)• “Cancellation”

• Gain, phase critical

• Need for minimum phase network, compensation

• Recognition of limitations• Non-flat component response

• Phase shift due to components, acoustics

€

ER = 20logEd2 + Ec

2 − 2 Ed Ec cos θd −θc( )

Ed


Meeker 1958

• Feedback system (System II)

• More tolerant to amplitude error, phase accumulation

• Noise amplification out-of-band

• Stability & robustness• Unity gain (0 dB) @ ±120°, -20 dB @ ±180°

• With 3 dB noise amplification, 0 dB @ ±138°, -10 dB @ ±180°

€

R = 20log1+ T2 ƒ( )

R = 20logT2 ƒ( )


Meeker 1958

• Role of transducers and transfer paths• …. “substantial phase shift above 500 cps”

• … “correcting network”/ “compensation network”• Cut and try compensation!

• Implemented RC network filter for compensation at low and high frequency


Meeker 1958

• Issues and opportunities• Stability and gain in useful band

• Components of the day the limiting factor

• 20 dB reduction from 50 cps to 400 cps reasonable


Meeker 1958

• Free-field sound absorber• Concluded not viable due to constrained volume

of effectiveness

• Still an area of research


Meeker, “Active ear defender systems: development of a laboratory model,” WASC

TR 57-368(II), 1959

• Feedback system prototype

• Addresses transducer development/limitations• Microphones

• Earphones

• Amplifier phase shift limited performance

• Alternative embodiments• Semi-insert

• Co-axial (close-coupled speaker and microphone)


Meeker 1959 Feedback ANC experimental results

110 dB max noise field


Meeker 1959

• Semi-insert concept


The art as of 1959

• Feedback system preferred embodiment

• Need for:• Compensation for transducer dynamics (“equalization”,

“correcting networks”, “compensation networks”)

• Minimum phase designs, from all components

• System design considering all elements

• Higher power handling components


Patent: U.S. Patent US 2,972,018. Filed: Nov. 30, 1953, Patented: Feb. 14, 1961


The 1970s

• Dorsey et al., “An active noise reduction system for use with ear defenders,” 8th International Aerospace Symposium, Cranfield, 1975.• Addresses many of the same issues as Meeker et al.

• “Surprised” by transducer affect

• “Equilisation philosophy” - compensation

€

T s( ) =s2 + 2ξ1ω1s +ω1

2

s2 + 2ξ2ω2s +ω22s +α

s + β


The 1970’s

• Dorsey et al.• Showed ~10 dB reduction 150-700Hz, 20 dB 300-600 Hz

• Up to 6 dB amplification 1-3 kHz

• Low-frequency performance limited by earphone actuator phase shift, oscillation

• 124 dB noise field target


The Bose Era

• Patents and publications galore• A. G. Bose, and J. Carter, Headphoning, U.S. Patent No.

4455675, June 19, 1984


The 90’s and beyond: digital control

• Pan et al., Application of feed-forward active noise control to a circumaural hearing protector”, Active 95.• Off-line error path estimation


Pan et al. Active 95

• Band-limited noise 40-750 Hz, tones, chirp


Casali & Robertson, “Narrow-Band Digital Active Noise Reduction in a Siren-

Cancelling Headset: Real-Ear and Acoustical Manikin Insertion Loss,” NCEJ 42(3), 1994

• Adaptive digital version of Olson’s sound absorber


The Consumer Side

• NoiseBuster headphones use a microphone inside and outside the earcup (1) to listen to the noise coming into the ear (2). Using electronics (3), the system takes that information and uses it to create a noise wave that is identical to, but directly opposite of, the one coming into the ear (4). The "anti-noise" wave is output through a speaker, also located in the earcup. When the two waves (the noise wave and the anti-noise wave) meet, the noise is significantly reduced (5). $69

• Active cancellation: 40-1,200 Hz, maximum 18 dB between 100-200 Hz

Amazon.com


The Consumer Side

• Acoustic Noise Cancelling® Headset Technology

• The story of this breakthrough technology begins on a long-distance flight that Dr. Amar Bose took in 1978. When he tried on the airline's conventional headphones, the experience was disappointing-engine roar and other cabin noises interfered with any enjoyment of music. Turning up the volume did little to mask the noise and further distorted the music. Would it be possible, he wondered, to achieve active noise reduction in a pair of headphones to enhance the enjoyment of music?

• Dr. Bose's experience on that flight prompted the creation of the Bose® Noise Reduction Technology Group. They, in turn, developed Acoustic Noise Cancelling® headset technology to dramatically reduce unwanted noise and allow the enjoyment of music, films or even silence, in places where noise is a problem.

• $299

Bose.com


The “Remaining” Issues

• Transducer dynamics

• Compensation

• Acoustic path limit

• Low-frequency performance


Where we stand

• Push to higher noise level systems (140 dB+)

• Push to lower & higher frequencies

• Adaptive/feedforward/feedback

• 100’s of publications, patents, etc.

• Stay tuned for the next presentations!


Fertig


The Issues

• Forward-acting

• Feedback

€

ER = 20logEd2 + Ec

2 − 2 Ed Ec cos θd −θc( )

Ed

-20

-10

0

10

20

30

40

10 100 1000 10000

Frequency, Hz

Gain, dB

020406080100120140160180

Phase, deg

Gain

Phase

€

R = 20log1+ T2 ƒ( )

R = 20logT2 ƒ( )


Carter, “Active noise reduction,” AFAMRL-TR-84-008, 1984

• “Classical” feedback w/compensation• 10 dB reduction 50-500 Hz

• 20 dB reduction 80-300 Hz


Carter 1984


Carter 1984

• Adaptive feed-forward concept

• Considered “too expensive”

integrated acoustics laboratory active noise reduction hearing protectors: 50 years of development...

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