[shadow82x]

I'm not sure if I'm going crazy here or not. But I recently tried out and briefly reviewed the Klipsch R6M. I ordered a second one with the intention of returning the first because the remote was acting funky on my original. So I open up this second one, without burning in, and it sounds completely different than my original one. I've been doing some A/B testing between the two, and the sound signature is really pretty different. My original pair has a boomy bass with the vocals sounding sort of distant. My new pair has the bass toned down and the vocals definitely have greater clarity than the original pair. Is this something that is pretty frequent between headphones or is is this a rare situation? I didn't think I'd see the day where two earphones with the same driver would sound noticeably different. 
 
Both pairs of earphones were barely burned in. The original pair had been used normally for a few weeks, but I doubt that would make the bass stronger. Or does it?

 

[H20Fidelity]

I totally believe you 100%. In my time using IEM here I've heard differences between x2 pairs of:

Westone 4
Brainwavz B2
Ostry KC06.

These are IEM I've had right beside me at the same time and almost gone mad A/Bing them

This is why I keep saying its amazing anyone actually agrees on sound signatures and presentation here on Head-Fi because I have heard differences more than enough times to know that there's (sometimes) tolerance variations between the same product. Would explain why member A and member  B disagree completely (which I also see all the time)
 
Anyway, pick the one you like the most and return the other.

 

[Head Injury]

Every driver ends up sounding a little different. Even the left and right driver in the same pair will measure different, manufacturers take care to pick out two drivers for each pair that measure as close as possible to each other, at least in high-end pairs. Most of the time the differences are smaller than the one you've found, but you can find some great examples of poor channel balance on InnerFidelity.

 

[H20Fidelity]

Here's another example I read the other day.

http://www.head-fi.org/t/746228/rockjaw-alfa-genus-reviews-impressions-thread/30#post_11197054

To continue further, there's two other IEM I've heard  (at the same time) which sounded different as well. However as my personal choice they will remain unnamed. So that's five in total I have heard with differences.
 

 

[gradesm]

It's pretty common I guess. I've seen relatively decent reviews on the Brainwavz S0. But the pair I got sounds no where near what was described. I'd venture to say it's the worse sounding phones I've ever heard(yes, worse than stock buds from any device).

 

[lin0003]

Maybe one pair is burned in more if you believe in that. 
 
Like others have mentioned each set will sound slightly different, but most of the time it is not detectable by just listening to it. 

 

[jay567]

With seriously well developed second hand market for IEMs in Korea, I went through a ton of same IEMs and yes, for my experience, more often than not, after burn in (possibly pre-burn in too but I don't know for sure because I dealt with a lot of second hand IEMs), they tend to sound different than same with some difference being so great for me to say, "I am digging this TF10 but absolutely can't stand that TF10" in many cases. However, I noticed some IEMs tend to vary more than some IEMs which I guess is natural.