[bashinator]

Exactly. With my Etymotics in-canal buds, I can set the volume on my music player to about 25-30%. With the stock buds or even non-isolating over-the-ear headphones, the same subjective loudness requires about 60-75% on the volume control.

[markrages]

This is not a good measure, because different earphones have different efficiencies.

And the type of earphone changes the efficiency as well: The sound from the Etymotics all goes to your ear, but the others waste some sound out of your ear.