In other words... the iem can maybe more efficiently transfer pressure to the ear drums at low frequency than some other speaker. That pressure is called VOLUME. So what? We're saying iem's are efficient? (duh) bass heavy?(depends on the iem I guess) We're saying they're too loud? You don't have a volume knob? This is all still just volume. What's being tossed around is the idea that there is some kind of voodoo oscillatory pressure on an ear drum that is not related to volume, that's pushing harder than it sounds like it's pushing. That sounds like bunk to me. Your ear drum either has pressure or it doesn't and you can convert that pressure from time domain to frequency and that's the volume of the various frequencies. That's it. There's no voodoo silent pressure.