The Right Headset in Your Fixed-Wing Aircraft
CW4 Paul Miller, CW4 David Littner, CW4 David Keshel, CW4 Elza Brokaw, and CW3 John J. Lill WOSC 05-03
Editor’s note: The active noise cancellation and active noise reduction (ANC/ANR) headsets are only appropriate for “fixed-wing” aircraft. This technology cannot be used in rotary-wing aircraft because the equipment defeats the lateral impact protection of the helmet.
As a crewmember, precise communication is imperative for crew resource management and mission success. According to studies done by Frederick V. Malmstrom, Ph.D., active noise reduction headsets significantly reduce pilot’s physical and mental fatigue, as well as loss of proficiency during flight.
In years past, there could have been a misconception that David Clark headsets were the only ones the Army allowed. This was because units were making unauthorized modifications to aircraft electrical systems to power other headset systems. The U.S. Army Aviation and Missile Command (AMCOM) fixed-wing program management office (PMO) determined that battery-powered aviation ANR headsets are authorized as long as no modifications are made to the aircraft. Many units have locally procured such headsets and have had great success with off-the-shelf ANR products.
The principle of the ANR headset is to cancel unwanted low-frequency noise. Unwanted noises are those sounds that interfere with the pilot’s reception and understanding of crewmember and air traffic control communications. Passive attenuation of high-frequency noise is accomplished mainly through the ear cup, noise-absorbing padding, and secure fitting ear seal design. By placing a miniature microphone inside the ear cup, noise entering from the flight deck through the ear cup is sensed and analyzed by an electronic circuit. The electronic signal is inverted, amplified, and transmitted through the earphone canceling out the noise, whether you are actively talking or just listening to the radio or another crewmember. Most of the electronic noise-canceling technology headsets are failsafe in that they provide individual circuits for both the ANR portion and the radio/intercom portion of the headset. If the headset power source (battery pack) or ANR electronics fail, the headset will continue to function for communications.
In accordance with testing performed at the U.S. Army Aeromedical Research Laboratory, Fort Rucker, AL, by Dr. A.J. M. Houtsma, Ph.D., both the Bose AHX 32-01 and David Clark (DC) P/N 40862-01 perform very well at reducing exposure to hazardous noise levels. Testing was performed at a flat 108 dB(A) for frequencies starting at 63 Hz extending to 4,000 Hz.
The two headsets tested took very different approaches to reducing noise attenuation with both passive and active technologies. The DC P/N 40862-01 performed very well with passive attenuation at all frequency levels, mostly attributed to the heavy construction of the plastic shell, noise-reducing materials within that shell, and the gel-type ear cups that conform very well to the contours of the skull around the ears. With the ANR off, the DC headset reduced the sound level below the Army’s 85-decibel threshold for hazardous noise, and above 300 Hz, reducing it below the OSHA standard of 80 decibels. After turning the ANR on, this headset performed very well at reducing the low frequencies well below the 80-decibel level and maintained the higher frequencies well below 80 decibels. The effect of ANR is very noticeable.
The Bose model AHX-32-01 did not provide low frequency passive noise attenuation below 200 Hz, and reduced the noise level below the Army 85-decibel threshold at approximately 300 Hz. In the higher frequencies, the Bose provided very effective passive noise attenuation. After turning the ANR on, the Bose reduced noise attenuation below the 80-decibel OSHA standard across the frequency spectrum tested.
Marketing by both companies highlights findings in this unsolicited study of two commonly used ANR headsets. The DC headset is very good at passive noise attenuation in low frequencies, such as for propeller-driven airplanes, and does a good job in the high frequencies. The DC headset provides noticeable ANR especially good in the above applications. The Bose headset is more lightweight and may be more appropriate for long mission profiles based on interviews with pilots who have used both products. The ANR headset is better suited for use in jet aircraft where there is considerable noise energy above 1,000 Hz in comparison with propeller aircraft. Pilots have commented that the Bose audio clarity is excellent. No matter the make or model of headset, many studies have discovered significant reduction in performance when an eyewear frame breaks the seal of the ear cup. Caution must be taken to minimize the eyewear structure penetrating the seal. Using wire-style frames may help preclude this problem.
Individual units will have to decide which headset is appropriate to meet their needs. Many products are available through FEDLOG and commercial venders with government sales representatives are ready to assist your needs. The David Clark model is approximately $300 less than the Bose, both having a 5-year warranty. For more information, log on to their Web sites:
http://www.bose.com/ and
http://www.davidclark.com/.
--This article was written by CW4 Miller, CW4 Littner, CW4 Keshel (team leader), CW4 Brokaw, and CW3 Lill as a class project while attending the Warrant Officer Staff Course 05-03 at Fort Rucker, AL.