A procedure of decibel conversion for SPL fitting using insert earphones

Tomizawa Akifumi, Sakata Hideaki

doi:10.4295/audiology.54.123

The purpose of this study was to verify the validity of the conversion procedure for a hearing aid prescription based on deriving dB sound pressure level (SPL; 2cm³ SPL or ear canal SPL). The procedure used dBHL audiometric data obtained with insert earphones, adding the coupler-to-dial difference (CDD) and the real-ear-to-coupler difference (RECD) to convert the data to SPL. To evaluate the acoustic factors affecting the CDD and the RECD, the difference of the acoustic level between 2 insert earphones (3A and 5A) and between 2 types of 2cm³ couplers (HA-1 and HA-2) were measured. The RECD and the real-ear-to-dial difference (REDD) of the direct output level of the audiometer were measured in the real-ear worn 2 acoustically modified earmolds, with a FONIX FP-35 probe tube-microphone system. The predicted REDD (CDD+RECD) values were compared to the measured REDD to verify the converting procedure. The results showed that the 2 insert earphones were acoustically different within 5dB in the 200∼4000Hz range and over 10dB at around 6000Hz. The difference between the 2 couplers increased as frequencies rose above 1000Hz. The predicted REDD corresponded to the measured REDD within 250∼4000Hz in each earmold, the difference did not exceed 3dB. The results demonstrated the converting procedure was valid and reliable for dB transformation. The CDD measured for an individual audiometer and the RECD measured in the real-ear can be used for deriving the SPL.

A procedure of decibel conversion for SPL fitting using insert earphones

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