You’ve Just Measured the REDD Real Ear To Dial Difference
For example, let’s assume LDL at 1000 Hz was 90 dB HL and 110 dB SPL on the monitor.
The REDD at 1000 Hz is 20 dB (110-90)
If threshold at 1000 Hz is 5 dB HL, then threshold in dB SPL is 25 dB SPL (20 + 5).
Complete conversions at the other audiometric frequencies and add that amount to threshold dB HL and you have just mapped threshold in dB SPL.
Can not directly measure “threshold” due to noise floor of room and microphone.
Assumes attenuator of audiometer is linear!