They cost $499 but maybe they are even better than the Etymotic ER-4s which cost around $299.

Look at the specs of the E5C--they'll probably sound even better than the Ety's (but this is subjective), but I think you're going to need an amplifier to drive them, whereas the Ety's don't need an amp. I've yet to see a post from anyone whose actually tried the E5C; love to hear from anyone who actually owns a pair...

I was under the impression that E5Cs are very sensitive

Yes, you must talk to them kindly, or there feelings will be hurt.

Seriously though, check out the impedance--it's way up there, so regardless of how sensitive they are, I think you're going to need an amp to drive them with the ipod. These things have dual drivers, I just don' t think they'll work very well without an amp.

I thought a higher impedence generally leads to higher sensitivity. At least that's how it works in hi-fi applications.... people with low-power tube amps have better sound "generally" with higher-impedence speakers.

Someone correct me if I'm wrong.

D

But my understanding is the higher the impedance, the more "juice" you're going to need to drive them (at least in the scenerio of earphones). So, the E2's, with an impedance of 16 ohm, are very easy to drive. The E5's, with 100 a whopping 100 ohms impedance, are gonna need a little oomph. I'm still trying to figure out how the impedance and senstivity relate--ie which is more important...

You are correct, lower impedance = higher sensitivity. Basically it means with one unit of power (say a watt) how loud will the speaker be at a given distance. Lower impedance = equals higher volume = higher sensitivity

The regular Apple earphones are 32 OHM. The shure E2c are 16 OHM so does that mean i should get more volume out of the shure E2cs ?

Yes--at the same volume, the Shure's are perceptively louder. But if you really want to see a difference, do a direct comparison between the EX's and the Shure's--the Shures are incredibly more loud thant the EX's at the same volume setting. I don't know what the impedance is of the EX's, but I'm betting it's relatively high...