Deriving the Real-Ear SPL of Audiometric Data Using the “Coupler to Dial Difference” and the “Real Ear to Coupler Difference”

In Brief 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. Although a probe-tube microphone can be used to measure real-ear sound pressure level (SPL) directly, it is not always possible to undertake extensive real-ear measurements in certain populations, especially infants and children. The purpose of the study was to compare the measured real-ear 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. The study used 16 normally hearing subjects with the CDD and RECD measured in an HA1 and an HA2 2-cc coupler using an EAR-LINK foam ear-tip and a customized earmold. 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. This means that a valid estimate of real-ear SPL can be obtained using the CDD and RECD when it has not been possible to measure real-ear SPL directly.