Miniature microphones and their use
ISVR Consulting uses two main methods of measuring noise levels at the ear and assessing noise exposures under headsets, helmets, earpieces and earphones. One method uses an acoustic manikin or Head and Torso Simulator which has the dimensions and acoustical properties of a median adult. The other uses miniature microphones to measure the sound at the ears of human listeners. This technique is known as the ‘MIRE’, or Microphone In Real Ear, method. Whether the manikin method or the MIRE method is used depends on the application, as each has advantages and disadvantages. At ISVR Consulting we use both methods.
Examples of the use of miniature microphones and the MIRE method
Two types of miniature microphone with a 5 pence coin
A Yamaha Rhino off-road vehicle
A National Police Air Service EC135 helicopter
The MIRE method is particularly useful when a real person has to be present, to ride a motorcycle, for example. At ISVR Consulting we regularly use two types of miniature microphone, as shown in the photograph, and the choice depends on the application.
We have used miniature microphones to measure the noise reaching real ears for various applications:
- under earmuffs for assessing hearing protection during firearms training on indoor and outdoor ranges,
- under motorcycle helmets, in the windtunnel and on the road
- under helmets worn by users of off-road vehicles
- under marine safety helmets for crew of rigid inflatable boats (RIBs)
- under crew flying helmets in helicopters during flight, with active noise reduction systems switched off and on
- for measurements of the insertion loss of hearing protection and flying helmets in the laboratory to American Standard ANSI/ASA S12.42-2010
- measurements to BS EN ISO 11904-1:2002 Acoustics. Determination of sound immission from sound sources placed close to the ear. Technique using a microphone in a real ear (MIRE technique)
Other uses of miniature microphones
We have also used miniature microphones to measure and record noise levels in situations where their small size and unobtrusiveness is an advantage, and where normal microphones and preamplifiers are not convenient or practicable.
We used miniature microphones, for example, to measure the noise levels during aircraft cabin evacuation trials, and to measure the noise levels produced by aircraft cabin watersprays. (Published as D M Bottomley1, H C Muir1 and M C Lower2, 1993; Aircraft evacuations: the effect of a cabin water spray system upon evacuation rates and behaviour. CAA Paper 93008. Civil Aviation Authority, London. ISBN 0 86039 547 2. 1Cranfield University, 2ISVR Consulting, University of Southampton.)