Looks and Functionality!
My prior experience with headphones has been with ear buds or "on the ear" headphones (ones that rest on your ears). With those as a frame of reference, I truly appreciated the circumaural design of the Sennheiser HD 580s. Each earpiece is a huge cup that surrounds and envelopes your entire ear. No pressure is placed on the cartilage of your outer ear, which means superior comfort, compared to some headphones that rest on your ears. Also, each ear cup is made from black, padded velvet. They're luxuriously soft and comfortable, so much so, that we likened these headphones to wearing pillows over your ears - yes, these 'phones are that comfortable! An added bonus is that they do a darned good job of keeping my ears warm in this hyper air conditioned office. Rounding out the comfort factor are the four cushions that line the headband portion. This relieves pressure on the top of your head, and represents the icing on the cake as far as comfort is concerned.
The HD 580s come with a 3 meter long copper cord, which is convenient because with that kind of length, you'll likely not need extension cord to get to your sound source. Also, the cord is detachable for easy replacement: a sharp tug will separate the two pronged plug that goes into each ear piece. The headphone plug is a gold plated, 3.5 mm (1/8 inch) stereo plug, but if you need a 1/4 inch connector, fear not - the HD 580s include the 1/8 to 1/4 inch adapter, which also appears to be gold plated. The HD 580s are cased in a hard, gray plastic - there is some metal in the headphone, mainly for the expandable headband, but for the most part it's plastic, which keeps the phones very lightweight for its size. Don't let the word plastic fool you though. The Sennheiser HD 580 is a solidly built headphone, and will last you for years, barring any catastrophes (like spilling coke all over it or stepping on them).
The cord is detachable
The Sennheiser HD 580s feature an "open" design, which means that the casing that surrounds the headphone drivers doesn't seal out the outside. The advantage to this is that it lets your ears "breathe" a little bit better, but you're not as isolated from outside noises. Protecting the drivers is more of that stylish gray plastic, molded in a brick-like grating pattern. The headband is expandable of course, to fit bigger craniums. Also notable is that the ear pieces swivel in four directions instead of two. Most headphones allow the ear pieces to swing from top to bottom. The Sennheisers do this but also allow a bit of lateral motion to contour fit your face perfectly. The only downer here is that motion in all four directions is very limited. You can't fold these up like you can with the Sony MDR V600s. Overall, the Sennheisers are a solid, comfortable, and good looking set of headphones, which is more than can be said for other brands like the Grado SR 60s.
Check the right sidebar for the technical details. Just to go over a few highlights, the frequency response for these headphones ranges from 12Hz to 38,000 Hz. That is, these headphones can produce sound all the way across the sound spectrum from those two points. I thought that was interesting because humans are only supposed to be able to hear up to 20 or 22KHz. Perhaps only your dog can fully appreciate these headphones ;) Also, the total harmonic distortion is under a tenth of a percent. Yowzaa! That's some accurate sound reproduction!