So, I finally convinced myself to buy an iPod a couple of weeks ago. Next had to be a decent set of earphones -- my set of Etymotic Research ER-4P arrived yesterday. Etymotic makes several versions of this earphone. Among these, the ER-4S version is more of a audiophile home-use version, and the ER-4P model which features lower impedence, so as to get more volume out of smaller, portable device amplifiers such as that in the iPod. They may have lower impedence, but I still found myself listening to my iPod at about the same volume setting (85% or so) as with the stock phones... but I did seem to notice one big difference outside of the much-improved sound: the battery seemed to drain much quicker. I know next to nothing about the electronics behind this, but my experience tells me that at lower impedences my bass amp runs hotter - so it would make sense that it is using more power than with a higher impedence cab setup. I know that my bass amp is much louder sounding running at 4 ohms than 8, but I can imagine and guess that while the new phones have a lower impedence, other factors (e.g., a cleaner, distortion-free sound) conspire to make their *apparent* loudness pretty close to that of the higher-impedence stock phones. If my thinking is correct, at the same volume/EQ settings, lower impedence phones will use more battery power than high impedence phones. So, is my little theory on target, or is it off base?