Experimentation to Address Appropriate Test Techniques for Measuring the Attenuation Provided by Double ANR Hearing Protectors
Abstract
Increasingly the military environment can involve exposure to high levels of noise; levels of up to 150dB are anticipated (in some quarters) for deck-crew and ground-crew working with the Joint Combat Aircraft. In order to protect the hearing of personnel in high levels of noise, the use of double protection (earplugs worn in conjunction with earmuffs) is also increasing. Active Noise Reduction (ANR) systems are now widely incorporated into headsets and have also been incorporated into personally moulded earplugs. Therefore, the combination of an ANR Headset and ANR earplugs is the next obvious step in reducing high levels of noise at ear. Difficulties arise in determining the appropriate technique for establishing levels of sound attenuation achieved by the use of this Double ANR system. The Real Ear At Threshold (REAT) method has the advantage that it is a measure of the noise perceived by the subject. However, it can result in masking errors at low frequencies due to physiological noise. REAT cannot be used with ANR devices since the electronic noise of the ANR circuitry at approximately 1-2kHz will raise perceived threshold at this frequency range. The Microphone In Real Ear (MIRE) method has the advantage that it measures the absolute sound pressure levels in the ear canal and can be used with ANR devices. However, this technique does not necessarily measure what the subject hears, as it cannot measure the sound transmitted to the inner ear via routes other than the primary path of the ear canal. The personally moulded earplugs used by QinetiQ have been designed to incorporate microphones at the tip to measure the sound pressure level within the ear canal, and the sense microphone of the ANR earplugs can also be used to measure the sound pressure level within the device. Experiments using ANR headsets in conjunction with passive personally moulded earplugs were used to compare REAT and MIRE methods and to show the differences between the techniques.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 2005
- Accession Number
- ADA454478
Entities
People
- Christopher Tubb
- Soo H. James
- Susan E. Mercy