A few pages back luisdent gave his impressions of the differences. And basically he said its in the low end boost. And it's done well enough not to affect the other frequencies. So it's basically do you want flat or flat with a little extra low end?
Pretty much.
What I do like about the XR, is that if I'm listening to it and I don't consciously think about it, I don't usually feel there is too much bass. it just sounds like a great etymotic sound. However, when I compare them one after the other, the SR always leaves me thinking it is more transparent, and that there is absolutely no midbass masking anything. If you never told me I was listening to an XR however, when I compare them one after the other, the SR always leaves me thinking it is more transparent, and that there is absolutely no midbass masking anything. If you never told me I was listening to an XR, I might not immediately notice it, until certain music revealed the additional bass or I listened for a bit linger and started to feel there was too much warmth or not enough treble transients. But it never strikes me is blatantly different.
I'm pretty sure if they only released the ER4XR, I would use it and never look back. But of course they did release two models, so I'm just particular to the SR for it's slightly more transparent sound.
I had to have and compare both myself. But for anyone worried about bass in the slightest bit, the XR offers almost the same exact sound as the SR but with a bit more bass. And comparatively, every other earphone has a lot more bass and a lot less accurate treble.
I'm definitely not trying to hurt the sales of the SR, however I would put it down to this. If you are coming from a different earphone the XR is a very safe bet. If you are coming from the ER4S, then the ER4SR is going to be very, very similar with slight improvements in sound and physical design. So if you are very happy with your ER4S, I wouldn't hesitate to buy any ER4SR. You may like the XR, and by all means try it if you can, but i would get the SR if you can only get one and not look back.
If rather, you are coming from an ER4P, then the issue becomes one of bass alone. Both new models give you the improved treble. But having the improved treble, you may find that the bass seems to be less relative to the treble that is now better. Although, you may not.
But I would say the ER4XR is probably a more appropriate upgrade for users of the P. But that's subjective and more just a personal opinion based on how i would expect P users to want the bass region to sound....