An active noise reduction system for flying helmets and ear protectors

Abstract

One of the major limitations of flying helmets or hearing protectors is their inability to provide adequate acoustic attenuation at low frequencies. In both fixed and rotary wing aircraft and in armored fighting vehicles, the high levels of low-frequency noise cannot be suitably reduced by the use of passive hearing protectors alone. The development of active noise reduction for use in such protectors allows much of this limitation to be removed. This paper describes the development and testing, both in the laboratory and during flight trials, of an active noise reduction system fitted to the current UK military force's flying helmet. The system was developed under a Ministry of Defence contract by the Institute of Sound and Vibration Research at Southampton University, and assessed by the RAE in a number of helicopters and during high-speed, low-level flight in a strike aircraft. The results from both the laboratory testing and from the flight trials are discussed, and the operational and medical advantages of using this type of active system summarized, both for military and civilian use.