pietcux
Headphoneus Supremus
It actually has three modes:
NC standard mode
NC Aware mode
NC off mode
NC standard mode
NC Aware mode
NC off mode
Well, I have owned them both and the QC 25 win hands down in sound quality in my opinion.
Add to that the same superior noise canceling without the hiss plus the ability to use the QC25 without power makes it the biggest no brainier choice, unless you are getting a significant discount.
I just recently re-purchased the QC15, and to be completely honest they have better sound quality, at least to my ears. The QC25 and QC15 have overall the same sound staging, but I just felt that the 15 had a more detailed treble and mid range, but had less bass which to me is a good thing. I could hear the air coming off of guitars and other instruments better, the inhaling of singers, and female vocals just sounded richer and brought forward on the QC15's. The QC25 sounds like they traded treble for more bass, and sacrificed some of the midrange separation to top it off.
I had both and sold my QC15. I am mostly going from memory now, but I found the QC15 treble more harsh, the bass was more boomy and not as deep. The QC25 while cut from the same cloth as the QC15 just sounded more refined, so I sold the QC15. I wouldn't say night and day difference, but it seemed pretty obvious. I tried it on every kind of music, acoustic through rock and IDM. Plus as Zimmy68 says the much lower hiss, better NC and ability to use without batteries are all appreciated.
Maybe there is something wrong with the QC25s you have?
I just recently re-purchased the QC15, and to be completely honest they have better sound quality, at least to my ears. The QC25 and QC15 have overall the same sound staging, but I just felt that the 15 had a more detailed treble and mid range, but had less bass which to me is a good thing. I could hear the air coming off of guitars and other instruments better, the inhaling of singers, and female vocals just sounded richer and brought forward on the QC15's. The QC25 sounds like they traded treble for more bass, and sacrificed some of the midrange separation to top it off.
The same with me. I switched back to QC15 from QC25. I find QC15 overall sound quality better than QC25. Also the hiss(white noise) on QC25 is noticeably louder than on QC15.
By the way, I tried two QC25 sets. When I got the first set of QC25, I though that it must be defective - sound quality and hiss should not be worse than QC15.
But the second pair of QC25 was the same as the first one, so I switched back to QC15. I also like that ear cups on QC15 are a bit softer than QC25.