For anyone new to audiophile headphones, you may be surprised to learn that Sennheiser is THE name in the audiophile headphone business, and have been for some time now.
In case evidence would help you:
1)Ask the pros - HD600s are popular in serious studio recording, where sound quality is all-important.
2)More expensive is not necessarily better - other companies use their names or unnecessary and expensive materials to bump up the price....
3)Sennheiser is interested in "true sound", and, accordingly, puts into their products the right materials and excellent acoustical engineering. Everything in the 555s is for sound quality and comfort and durability. (Some headphones use wooden shells, fancy materials, and other such gimmicky things...that's just plain stupidity if you consider the sound, but it gets buyers that don't know audiophile headphones.)
4)Open vs closed - sound is vibrations. The air needs to vibrate if you want good sound. Closed headphones may help cut out noise in some situations, but it will dampen the sound in all situations. (Sennheiser's audiophile line are all open.)
5)Look at the stats! - the stats alone are better than most...the 555s are, essentially, standard for audiophile headphones...595s, 600s, and 650s are better, but other brands have a tough time matching even some of the lower ones, such as the 515s.
6)Noise cancelling vs pure quality - I have tried Bose noise cancelling headphones, which attempt to advertise good quality, but in fact, the noise-cancelling mechanism calls for the "closed" type and, furthermore, functions by running a sort of noise-dampening frequency, which, sadly but inevitably, dampens the sound (and puts pressure on your ears). Nice feature for noisy situations. However, audiophiles typically seek out a quiet place to listen. (Although in my experience, 555s sound so much better I prefer not having noise-cancelling over lesser quality.)
7)Great entry level - as above, these are the standard within Sennheiser's line of audiophile headphones. Even so, if you are just moving up to this quality level, you would be surprised how clear the music is, how suddenly you can hear the details you have been missing...in comparison, ordinary headphones or other companies' headphones simply sound trashy - the pitches may be there and the general sound is there, but no tones, no flavor, no character, no spirit. You'll be surprised how much you have been missing.
8)Sound reflection - just as Bose uses sound reflection in its speaker systems, Sennheiser uses such technology to create a more real experience...thus, they work great for movies too. Instead of having half the orchestra on one ear and the other half on the other, it will seem more like you are actually in a concert hall. (Although, at this price level it still won't be perfect...still, it will be better than the vast majority.)
9)Sennheiser is legendary - Do you know what the world's best headphones are called? Try Sennheiser Orpheus. They were a limited edition, only 300 were made, and are reportedly absolutely surreal. (The Orpheus, being so rare, is not very available...the best price I have seen is $12,000, and that is IF they are for sale.) The 555s follow in grand footsteps.
Now, a few points of advice if you get serious with audiophile headphones and get 555s or better:
1)To use them to their fullest, try to use them through good hardware... (iPods and mp3 players are pretty good, but if you want to go all out you could get amps, etc.)
2)Healthy volume is 70 decibels or less (about 70% of the max volume on 555s)...and, sound quality is generally better if you don't force them all the way up. (Finding a quiet environment helps.)
3)enjoy