There seems to be life left in this thread, and the topic will likely remain relevant for some time, so here's my two cents worth.
Many of the posts in this thread comment on the noise isolating properties of closed headphones, and if you are concerned about keeping outside noise out or keeping your music from intruding upon others then closed back headphones are the way to go. But the original poster had asked about sound quality, and that is another matter altogether.
As has also been pointed out previously, we can not definitively conclude that the acoustic differences between one pair of closed back headphones and another pair of open back headphones are due solely or primarily to the ear cup type, IF we are only using those two samples as the basis for our conclusions. On the other hand, when we notice that virtually all of the open back designs have common sonic properties that differ significantly from closed back designs, we can safely conclude that those differences are due to the design. It's similar to an argument regarding automotive performance: if a V-12 Ferrari consistently leaves a four cylinder Toyota Corolla behind when drag racing, you don't need to put the Toyota's engine in the Ferrari and measure performance in order to correctly conclude that the designed performance differences are mainly due to engine differences. There are sonic differences between open and closed back designs. The bigger questions are: will you notice those differences and will you care?
I do notice those differences, and to my ear they are significant. However, based upon the comments of others, it is apparent that not everyone can hear them, or perhaps they do but they aren't listening closely. (I think one common characteristic of audiophiles is that they do listen closely, very closely. Music listening is not simply another activity, but is for the duration the entire focus of attention and concentration.) All of this having been said, one headphone type is not necessarily better than the other, only different.
Overall, I prefer the sound of open backed headphones. I won't try to describe the differences, for many others have already attempted to do so and in a manner far better than can I. I think they sound more natural, open, fuller, and so on. I have two pair of open backed, Sennheiser's HD650 and Hifiman's HE-1000, and they are (I think) standard setting. Yet, there are exceptions. I have just finished auditioning a demo pair of Oppo PM-3 phones, courtesy of the loaner program currently under way by Oppo. (Thanks guys!!!) I've found that I am a fan of planar-magnetic headphones, but when fully enclosed within the ear cup they lose that sense of air, expanse, and "reality" found in open-backed designs. BUT, I preferred the PM-3 phones to the HD650 when listening to natural, acoustic sets such as jazz, fingerstyle guitar, orchestral, and the like. Although I tend to prefer an open back sound, there are other considerations in play; I still preferred the HD650 for much rock and synthetic sounds. But not all.
I'd purchased my HD650's blind, having considered many of the opinions and reviews found online, primarily those here on Head-Fi. I have absolutely no regrets at having done so! All things considered, going in blind and unable to audition any of the better headphones, I'd say you can't go wrong with a well regarded pair of open backed phones. The only closed back I have heard that I often prefer to my HD650 are the planar-magnetic PM-3, but that sound may not be to everyone's liking or preference.
So yes, you REALLY can hear the difference between open-back and closed-back headphones. To me, and apparently to many others, the differences are obvious, and chances are they will be to you as well. I'm sure the originator of this thread has made up his mind long ago, and I wonder what his thoughts about all of this are now.
, open buds/phones are better imho. Nice open cans are really
