I said this long back - put me in a straight jacket and leave me with EP630 for 3 days. First, I will hate it, then I will get used to it, third day I will start to like some of it's signature features. That's what brain acclamatisation can do. It does not happen with IEMs these days, but it happens to me with sources. I initially did not like QA350 much at all, but once I got used to it, I thought it was better than Clip+. Since I started using QA350 -> UHA6S long enough as my primary rig, I have found it very hard to go back to Clip+.
I am agnostic on the topic of burn-in (may exist, may not exist, I don't care!). To me, it's one of those useless debates which won't reach any meaningful conclusion much like cables. I believe in tips though!
I do "burn in" even my sources (by burning in the IEMs / Headphones) before listening because I can afford to wait for 3-4 days or even 3-4 weeks, but I don't stop to notice the 'before' and 'after' changes at all. I've observed changes in a few, but I was never 100% certain that they were due to 'breaking in' of IEMs or headphones. For one, the 'changes' always occur with IEMs I initially dislike. I never wanted to break-in FX700 or EX-1000. Second, with no measurements to back me up, I am still in the subjective arena - not in the realm of objective numbers.
- For instance, GR07 seemed to be smooth at first, but became sibilant after 10 hours of use and in the end, seemed to have much less irritating sibilance after about 160 hours.
- Panasonic HJE900 changed dramatically after 12 hours of burn-in but then I also changed the tips, so I am never sure about that one.
- With Crossroads Woody Two that Brendon loaned me I could knock off 1-2dB in EQ adjustment (from -6 to -4 - something like that) for some peak (don't remember the frequency exactly) after 25 hours of burn-in. But even in that case, after I kept it unused for a couple of days, I went back to the old setting.
- I felt that with 80 hours of burn-in, ECCI PR401 had become "warmer", but then upon A:B-ing with RE-ZERO, I felt the relative differences I felt were exactly the same as in hour zero.
Audio memory is very cloudy, mood swings are plenty and taste wildly swings depending on the day. So, I don't know if these instances are placebo induced / dependent on mood / actual happenings.
Burn-in may exist, but I believe that the first 20-25 hours are crucial in terms of any wear and tear to happen and to get mentally adjusted to the sound. Some of the differences may be subtle enough not to be audible. It can offset the frequency response by a couple of dB here and there which can alter the perception, but I am not sure if it can change the
character of an IEM. M2 will remain softer in bass presentation no matter what. It would never become punchy like the thick noted TF10. Bass getting more extended can also happen due to difference in closely observing the phenomenon.
Even with same IEM differences (fresh and used), it can be brushed aside by 'manufacturing tolerances' / 'batch differences'. My friend ordered a couple of MEE M6 together once, burnt one of them for 50 hours, observed some changes, compared it against the fresh one and later reported not much difference between the fresh one and the burned-in one.
And why is the impact of burn-in always positive? What about more "burn outs"? Even dfkt who felt that IE8 "burned out" after 200 hours, said recently in abi
IE 80 are essentially the same as the IE 8, almost no difference is sound quality. Their bass appears to extend deeper with some tracks, but not with others. AB testing these fairly fresh IE 80 against my 3 year old (and daily used) IE 8 shows that burn-in or burn-out is pretty much bogus.
Countless threads or war of words exist on head-fi between objectivists and subjectivists with no apparent conclusions. Same story would happen here. One would be better served to read both the article and all the comments - would explain both sides of the story.
Testing the Audibility of Break-in Effects | InnerFidelity
Few other interesting threads:
A tale of 2 IEM's (Montser Turbine Copper 1 vs Monster Turbine Copper 2) How different burnin techniques gave me two unique IEM's
Burn-in. Real or not?