Can an expert please confirm if this is a not a terribly error ridden and inappropriate way to measure dbA output of headphones/IEMs?
I am trying to measure the dbA of sound going into your ear canal, whether by way of an IEM or headphone. I'm also trying to figure out at what volume level an IEM is equivalent to an over the ear. Same with speakers (I obviously know how to measure that, just put the meter in the air). This is just for fun/curiosity. For example, I seem to need 8-10 bars of volume on my LG G Flex phone to get my Shure SRH940 into the 70 dbA output area (average), but I only need 3 bars of volume on my Shure SE846 IEM to get into that 70 dbA range. Based on this, I put the headphone and IEM on at this purported 70dbA level, to see if my ears could confirm that they had the same volume, but ultimately I could not be sure because they sound so fundamentally different.
What do you guys think? Is there some horrible error being introduced by this measurement technique? Or is it good for an approximation?
First pic is how I measure dbA output from the IEM, and the second shows how I measure it from the headphone.