Page 26 - Winter 2010

AUDITORY AND ACOUSTIC RESEARCH AND DEVELOPMENT AT THE AIR FORCE RESEARCH LABORATORY
Richard L. McKinley
711 Human Performance Wing, Air Force Research Laboratory Wright-Patterson Air Force Base, Ohio 45433
“The acoustics research program at the Air Force Research Laboratory has been active for more than sixty years.”
Introduction
Since the days of the Wright broth-
ers flying their first airplane, noise
and its effects on hearing and
communications have been an issue in
the operation of aircraft. The Air Force
Research Laboratory (AFRL) conducts
auditory and acoustic research and
development programs addressing
unique Air Force needs relative to both
air and ground operations. These pro-
grams have focused on two major areas—(1) bioacoustics in the development of noise exposure criteria, hearing protec- tion, active noise reduction, voice communications, spatial auditory displays, and spatial hearing and (2) physical acoustics in the measurement, modeling, and propagation of aircraft noise. The acoustics research group at AFRL has been a leader in research and technology development including passive hearing protection, active noise reduction headsets and earplugs, 3-D audio displays, aircraft noise measurement and modeling, speech communication in noise, and national and international standards for over 60 years. This article is meant to give a flavor of the people and facilities at the AFRL acoustics group and the unique proj- ects they are conducting. To understand the current and future research it is helpful to first review some history and legacy work of this group.
A brief history
The acoustics research program at AFRL has been active
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for more than 60 years. A report detailing the literature cita-
tions from this period would generate a substantial technical document and a complete review is beyond the scope of this article. The purpose of this section is to give a few examples of projects, large and small, that have helped make the group, facilities, and research programs what they are today. There are five primary core technical areas that have been, and con- tinue to be, the focus of the AFRL acoustics group—(1) hear- ing conservation, (2) hearing protection, (3) speech commu- nication, (4) spatial hearing and (5) noise measurement and community noise modeling.
AFRL’s research investigating acoustics and the effects of noise on humans began with the arrival of Dr. Henning von Gierke from the Helmholtz Institute in 1947. Dr. von Gierke’s dissertation (Doctor of Engineering, 1937) described the pre- diction of noise levels and spectrum from jet flow, both sheet flow and conical flow. Soon after Dr. von Gierke’s arrival at Wright-Patterson, he was involved in the measurement of noise from the newly developed jet engines and the Air Force published the first hearing conservation regulation, AFR- 160-3, “Precautionary Measures Against Noise Hazards,” in
1948. This regulation required that exposures were never to exceed 95 deci- bels (dB) and were recommended to be kept below 85 dB. Later, in 1956, Dr. Horace (Hop) Parrack, an Air Force charter member of the National Academy of Sciences Committee on Hearing, Acoustics, and BioAcoustics (CHABA), led the establishment of the first recognized (military or non-mili- tary) comprehensive hearing conserva-
tion program.
AFRL has also been a leader in the development of both
passive and active hearing protection technologies. Dr. von Gierke developed a lumped parameter model of passive cir- cumaural hearing protectors which explained the basic rela- tionship between attenuation and hearing protector design parameters such as mass, volume, and headband tension. The Air Force, working with Radio Corporation of America (RCA), designed and demonstrated a working active noise
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reduction (ANR) headset in 1956–1957. This ANR headset
project, led by Willard Meeker, RCA, used electron tube cir- cuits about the size of a bread box, (Fig. 1), and also used a miniature microphone in the headset earcup. During this time, work on improved passive hearing protectors (both ear- muffs and earplugs), and communication headsets was being led by Dr. Charles Nixon.
Work in physical acoustics (1959–1961), led by Dr. von
3
Gierke, developed a broadband siren. This siren design,
capable of producing sound levels exceeding 170 dB Sound Pressure Level (SPL), would be later used in aircraft acoustic fatigue research and for human noise research involving the original seven NASA Mercury program astronauts (Fig. 2). The human tests were conducted to ensure the high levels of launch noise experienced in the Mercury space capsules did not adversely affect the astronauts.
Fig. 1. Active noise reduction headset and electron tube electronics, circa 1957.
22 Acoustics Today, January 2010