Real Ear Measurement
is a term used for all measurements done directly on the client's ear. These measurements can be done with or without the hearing instrument being worn. The reason to do Real Ear Measurement for hearing instrument fittings is because shape and size of an ear canal significantly influence a hearing instrument's performance.
Without Real Ear Measurement, only average data can be used. However, the shape of the ear is like a fingerprint ĘC for each person individual.
This can lead to over or under amplification as well as to too high maximum sound levels. For people as adults who can subjectively describe if they perceive sounds as too loud or too soft it may not be such a problem. However considering babies, small children or some mentally handicapped who do not have the ability to describe their perception verbally it can lead to the problems mentioned above.
How does Real Ear Measurement works?
Sounds are presented using a loudspeaker in front of the test person. A microphone is located close to the ear to measure the sound's intensity. A second microphone measures the sound's intensity directly inside the ear canal in front of the ear drum.
Knowing the sound intensity outside and inside the ear enables the fitter to determine the actual amplification and output what the test person receives through the hearing aid and make the appropriate adjustments.
Rea-Ear-to-Coupler-Difference is one form of Real Ear Measurement. Rea-Ear-to-Coupler-Difference uses the fact that many hearing instrument shops have a hearing instrument analyzer . This analyzer is frequently used to adjust hearing instruments for clients. However, the coupler used in such an analyzer most commonly has a size of 2cc which is much bigger than the ear canal with an ear mold inside. As a result hearing instruments adjusted by means of an analyzer will be too loud (especially for children with their very small ear canals). On the other hand, doing Real Ear Measurement as described above can be quite difficult because the child must sit still and may not make noise.
Rea-Ear-to-Coupler-Difference is the solution to this dilemma. In RECD a signal will be measured one time with the analyzer's coupler and a second time in the ear of the child while wearing the ear mold. Now, knowing how the hearing instrument performs in the ear and coupler the difference can be calculated - the RECD. The hearing instrument can now be adjusted in the hearing instrument analyzer taking its real ear performance into account.
Once Rea-Ear-to-Coupler-Difference data is obtained the child is not required to sit still during the adjustment. Even its present is not required and therefore has time to do anything else.