The PX-200ii I reviewed was purchased 2 years ago and has been used for about 200 hours. I was so happy with the EQ'd result that I decided to buy a new white one (mine was black). When I saw that J&R had some for only $49 USD I got one immediately. When it arrived I set up my 2 identical iPod Touch 64 gb players and plugged the 2 Headphones in for a comparison. Big difference in sound. Each iPod was the same - same exact content, same EQ setting. I had to play with the volume settings to get the midrange about the same for each headphone, and when all was said and done, I could see that the new PX-200ii had a much greater midrange output and consequently less bass and treble.

I went over every square mm of the new headphone to see if there was any difference between it and the old one, and could not find the slightest difference. There are so many details on the exterior of the PX-200ii that I would have expected a manufacturing difference after 2 years. The fact that there wasn't means either Sennheiser's QC is extremely tight or the new headphone may have been manufactured at or near the same time as the original one. The first thing I thought of when I heard the difference in signatures was the earpads, but checking those carefully the old pads looked pretty much the same as the new ones. Since I'm nearsighted I can see extremely well close up. But the old pads could have changed in some way that isn't noticeable visually or by squeezing them to check for density and flex, so maybe 100 hours or so on the new headphone will adjust some of that out.

The volume controls on each headphone were set at maximum, and I switched iPods just to be sure the 2 different players weren't making any difference. I also double-checked the differences with the Objective2 headphone amp using the FiiO LOD cable to bypass the iPods' volume controls. The O2 amp improved the sound noticeably, especially the bass, but didn't change the overall difference significantly. I will be using the new PX-200ii (mostly for portable use) exclusively for the next couple of weeks, so at the end of that time I'll retest them and see whether there is a burn-in effect or whether the earpads adjust somehow and if that makes any difference.