[gilsont]

I recently purchased the etymotic MC5 and found them to be surprisingly inefficient.
 
I read the specs of the headphone at 16ohms and 100db.
 
However, when compared to the other IEMs I own, these MC5 requires twice the amount of volume to sound even with my other IEMs which are similar in spec.
 
Am I missing something here?

 

[Spyro]

100dB is pretty low.  I can see what you are saying.  The more efficient IEMs are normally in the 112-125 range.
 
Maybe a safety hearing protection thing?  Pretty dumb.  It's just burns more battery time.