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Deriving the real-ear SPL of audiometric data using the "coupler to dial difference" and the "real ear to coupler
1Institute of Sound and Vibration Research, University of Southampton, United Kingdom.
Objective:
The purpose of the study was to compare the measured real-ear sound pressure level (SPL) of audiometer output with the derived real-ear SPL obtained by adding the coupler to dial difference (CDD) and real-ear to coupler difference (RECD) to the audiometer dial reading.
Design:
The real-ear SPL and RECD were measured in one ear of 16 normally hearing subjects using a probe-tube microphone. The CDD transform and the RECD transfer function were measured in an HA1 and an HA2 2-cc coupler using an EAR-LINK foam ear-tip or a customized earmold. The RECD transfer function was measured using the EARTone ER 3A and the Audioscan RE770 insert earphone.
Results:
The procedures were very reliable with mean differences on retest of less than 1 dB. The mean difference between the measured and derived real-ear SPL was generally less than 1 dB and rarely exceeded 3 dB in any subject.
Conclusions:
The CDD measured for an individual audiometer and the RECD measured for an individual ear can be used to derive a valid estimate of real-ear SPL when it has not been possible to measure this directly.
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