Considering how much I had to learn about 5.1 audio for a project I'm working on, lemme 'splain.
The "5" in "5.1" refers to the 5 speaker channels: Front left, center, front right, rear left & rear right, and the ".1" is the sub woofer, so
crudus, you are correct sir!
7.1 audio is the same as 5.1, but you have two "side" speakers as well.
As far as 5.1 surround headphones go, nobody even comes close to Psyko Audio. [http://www.psykoaudio.com/]
Psyko headphones are on the more expensive side, but if you want a balls out, rip your head off, hear the bad guys coming a mile away & shit your pants in a horror game kind of surround experience, save your pennies and get THESE. You won't ever use your speakers again.
All other surround headphones use small speakers embedded & angled inside the earpiece to "simulate" surround sound, but it isn't true dolby 5.1 or 7.1, and the "sub" is usually just a "thumper" against the back of your head which doesn't really do anything but annoy you, and the way most of them are shaped they either hurt your ears after a while or you sweat like a rapist in front of a female judge & jury. (Descriptive, huh?) But those crazy engineers managed to come up with a headphone design that might feel a little heavy at first, but the earpieces are so comfortable after a while you forget that you have them on!
If you want the technical mumbo-jumbo then check out the link above, but if you understand how a Bose wave radio works, you're already halfway there.
I personally would prefer to just have an insane surround setup in my studio, but A: I'm limited in space and because this room isn't that big anyway, surround speakers would be a waste of time, and B: I have neighbors. The Psyko headphones were the best money I've ever spent, and the best part?
The were invented by a CANADIAN, just like pretty much everything else America takes credit for.
Ok enough with the infomercial, click the link & see for yourselves
