Page 27 - Winter 2010

Fig. 2. High intensity noise test at AFRL, circa 1960.
In the late 1960’s, AFRL conducted the first and only study of the effects of airbag deployment on the human audi- tory system. These data were used to estimate the hearing damage risk (1-2%) from airbag deployment. During the 1960’s, the effects of high levels of infra-sound on human auditory, vestibular, and cognitive function were also investi- gated. At that time, rapid progress was being made in air transportation and consideration was being given to the US
development of supersonic transport. Dr. Nixon’s work on human responses to sonic boom4 was instrumental in the US policy decisions to prohibit commercial supersonic flights over the continental US. At the personnel level, a young Air Force Lieutenant, David Blackstock, had many debates with Dr. von Gierke regarding non-linear acoustics. Later, the Acoustical Society of America would separately award both men the Gold Medal, Dr. Blackstock for “contributions to the understanding of finite-amplitude sound propagation and worldwide leadership in nonlinear acoustics,” in 1993 and to Dr. von Gierke for “contributions to bioacoustics, psychoa- coustics, vibrations, and for leadership in national and inter- national acoustical standards,” in 1999.
The 1970’s brought development of speech recognition systems, speech synthesis systems, custom molded commu- nication earplugs, community noise mapping from aircraft operations, a voice communication research facility, Voice Communication Research and Evaluation System (VOCRES), shown in Fig. 3, and new work on active noise reduction headsets. AFRL human temporary threshold shift (TTS) studies were instrumental in adoption of the equal energy principle (i.e., the 3 dB per doubling time-intensity trading relationship for noise exposure). Led by Lieutenant Colonel Daniel Johnson and Captain Mark Stephenson, these studies showed that human TTS was essentially equal for exposures as short as 1 second at 130 decibels, A-weighted (dBA) and as long as 48 hours at 80 dBA (i.e., equal energy) . Coincident with the technology developments and pioneer- ing research was the development of national and interna- tional standards in physical acoustics, bioacoustics, and noise, led by Dr. von Gierke.
The 1980’s brought AFRL’s development of the world’s first real-time system for presenting synthetic spatial audio cues, (i.e., a 3-D audio display). This display was developed using the AFRL Auditory Localization Facility (ALF) shown
Fig. 3. Voice communication research and evaluation system (VOCRES), circa 1987.
Acoustics at the Air Force Research Laboratory 23