I guess I believe in a hint of break-in with headphones. Not 100 hours with a special white noise burn-in track to align all the electrons in the copper cable, maybe just 10 hours of rock n roll. Work the drivers a bit before doing the serious listening.
So I toss in a Judas Priest CD (Best Of: Living After Midnight) and put the player on repeat all. Lots of highs, lots of lows, lots of screaming guitars to really work the system. But I have to make sure the volume is set at a good level, right? So I put the Etymotics ER4-PTs in. Using the three flange tips that come on them from the factory, I put them in and encountered the best isolation I have ever experienced.* It was like being underwater. So quiet, so far removed from outside noises.
For what it's worth, I used the P to S adapter and the 1/4 connector. I set the volume on my Asgard 2 and went to remove the ER4s, and that's when I noticed the music. Now Judas Priest is probably not anyone's idea of an audiophile reference CD, but holy @#$! the sound was incredible. Amazing. Track 3 is a live version of "Breaking The Law." The bass on this track is a deep, throbbing, continuous assault on your ears (and entire body if you have a sub), and I love it. The ER4s nailed it. Deep, powerful bass, and lots of it.
So I wound up listening to the whole CD and I am already super happy with these headphones, without a hint of break-in. These rock right out of the box. I was hearing detail I've never heard before. Music like this can sometimes be overly bright but I didn't have any problems with that. The highs were high and clear and just about perfect. Vocals, well, they sounded great as well but this is not exactly the type of music for vocals. Soundstaging- the crowd noise on some of the live tracks- was quite wide and expansive. Some of the clapping and shouting sounded out of ear, which is a neat trick for in ear headphones.
Now to throw my usual, more beautiful reference tracks at these headphones. I can't wait to see how my favorite songs sound. Overall I am super impressed. Well worth the $299.
*To compare isolation, I own HiFiMan Re-Zero IEMs, Shure SRH840 closed cans, and MrSpeakers Mad Dog closed 'phones. The Etymotics are the best isolating, by far. I'm not knocking the sealing ability other headphones, just trying to say that the ER4s REALLY excel in this area.