Comparisons among SPLs in real ears, 2 cm3 and 6 cm3 couplers

Sound pressure levels (SPLs) were measured in the ear canals of 30 adult subjects with standard audiometric earphones (TDH-39) and insert earphones (Etymotic ER-3A) and compared to those generated in 2 cm3 and 6 cm3 couplers. Transfer functions are shown for real ear to 2 cm3 coupler, real ear to 6 cm3 coupler, 6 cm3 to 2 cm3 coupler, and dB HL under standard earphones to 2 cm3 coupler SPL. In general, the data agreed rather well with published transfer functions that in most cases were derived by adding together a series of partial transfer functions from various studies. The conversion values from dB HL to 2 cm3 coupler SPL could be useful in selection of certain hearing aid parameters, but the intersubject variability may limit their usefulness somewhat.