Bouchon d'oreille a attenuation active adaptee aux bruits d'helicoptere (Ear Plugs for Active Attenuation Adapted for Helicopter Noises) (Gehoerschutzstopsel mit aktriver Daempfung, geeignet fuer Hubschrauberlaerm)
Abstract
The helicopter noise spectrum is composed of two very distinct parts. The first is a low frequency component (<600 Hz) corresponding to noise from the motor. The second consists of the tonal components between 800Hz and 3 kHz characteristic of the noise coming from the gear reduction box. The classic use of a helmet for active attenuation to reduce this noise can pose a problem since the domain of noise amplification (rejectio) for this type of protection is often located in the domain of the tonal components. The use of an ear plug for active attenuation with a buckle against reaction should permit active attenuation up to 2kHz. In this case, using electrodynamic miniature loudspeakers (high volume auditory prosthesis) proves that such a system doesn't provide enough attenuation and/or is not steady enough. This problem especially concerns the tonal components that are not attenuated sufficiently. For the helicopter noise, a mixed system using two principles is proposed: the first, based on a buckle against reaction (feedback) is optimized for the low frequency noises (<600 Hz); the second based on the prediction (feedforward) permits to treat the tonal components to 800 Hz. This paper shows that such a protection for active attenuation is feasible and that the performance of the system is adapted to the specific needs.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 2006
- Accession Number
- ADA457175
Entities
People
- Karl Buck
- Veronique Zimpfer-jost