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Fig. 10. F-35 Lightning II, flyover noise measurement—clockwise from upper-left: the crew; flyover and tower sensors: ground sensors.
Marine Corps, and civilian sectors. Some examples of recent in-house and contract-developed technologies include the Attenuating Custom Communication Earpiece System (ACCES), high performance active noise reduction earplugs, helmets specifically designed to reduce bone conducted noise, tactical hearing protection (earplugs or earmuffs with active electronics to provide ambient listening, communica- tion, and localization capabilities while protecting from con- tinuous and impulsive noise—frequently also providing a radio communication interface), low-cost head orientation system, for dismounted airmen and soldiers, and spatial auditory symbology.
Recent work in ASA/ANSI standards include signifi- cant work on hearing protection standards S12.6, S12.42, S12.68, and on the speech intelligibility standard S3.2. Additional work has been accomplished in NATO Task Groups on impulse noise, active noise reduction, and improved hearing protection.
Physical acoustics
The efforts in physical acoustics are focused on the accu- rate measurement, modeling, and propagation of aircraft noise. The two major applications of the products from these efforts are community noise assessments and mission plan- ning. Most recently an extensive program was conducted to
measure F-35 Lightning II (Joint Strike Fighter) ground run- up near-field and far-field noise, flyover noise, and cockpit noise. The ground run-up, shown in Fig. 9, and flyover noise, shown in Fig. 10, data collection was conducted at Edwards Air Force Base in California. Recently, the Aeroacoustic Research Complex (ARC), Fig. 8, became operational and is being used to collect noise data on several aircraft. A collab- orative effort between AFRL and NASA also uses the ARC for data collection and analysis.
The propagation modeling effort has recently focused on adding capabilities to accurately propagate directional sources and handle non-linear propagation. This effort, the Advanced Acoustic Model (AAM), was a collaboration among the Strategic Environmental Research and Development Program (SERDP), AFRL, US Navy, Wyle Laboratories, and Penn State University. Validation studies for AAM are currently being conducted using data from very far-field (1 to 7 miles) measurement locations. A sec- ond SERDP sponsored effort is refining the process to esti- mate noise from jet flow characteristics. This effort is a col- laboration among SERDP, Penn State University, NASA Glenn, NASA Langley, Wyle Laboratories, General Electric Aircraft Engines, and AFRL. AFRL sponsors the develop- ment of many new technologies via Small Business Innovative Research (SBIR) contracts. One example is the
Acoustics at the Air Force Research Laboratory 27