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Dynamic Real Ear to Coupler Differences


The real-ear-to-coupler-difference (RECD) is the sound pressure level (SPL) difference between the 2 cc coupler as used in hearing aid specifications and measurements and the actual measurement obtained within a specific ear canal. In general, SPL levels are greater in the smaller ears of newborns and babies due to the smaller physical volume of their ear canals, than in adult ears. Therefore, RECD measures are of tremendous importance with regard to fitting amplification on pediatric ears.

Bingham, Jenstad, and Shahnaz (2009) evaluated 14 infants (aged 7 to 25 days) with normal middle ear status. Infants were tested on two occassions, approximately one month apart, using two RECD measures for each ear.

The authors determined that between the first and second visits there was a statistically significant difference (decrease) in RECD consistent with previous studies and revealing a decreased RECD (except at 250 Hz). Interestingly, although age was a significant predictor of RECD at 250, 3000, and 4000 Hz, age did not account for a large amount of variance, also consistent with previous studies. RECD values at visit one only statistically significantly predicted RECD values at visit two, for 3000 Hz. Thus, RECD values do not change at predictable or constant rates across infants. However, the mean change in RECD over a one-month time period (corresponding to the first month of life) is very small and not detectable due to test-retest variability of RECD measures--despite the statistical significance of the different RECD measures. Thus, re-test RECD measures during the first month of life are perhaps unnecessary as long as the transducer remains the same.

Bingham, Jenstad, and Shahnaz note that this conclusion cannot be applied over a time period greater than one month or after two months of age.

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