Do headphones requiere break-in?

Hi all! I just got a set of Grados SR60i headphones following some very good reviews about them, but I not happy with their sound: dark sound, rolled-off highs, bass wimpy, but the mids are ok. Do they need some break-in time to sound at their best? If so about how much time? Thanks!
My AKG's didn't open up until a couple hundred hours.
Yes, same for Sennheisers. Huge difference as they open up, especially highs.

Hi Tiofelon

From perusing threads in HeadFi various headphones do benefit from break-in according to the users there. With each set of cans it is different. I say give it about 50 to 100 hours. There is a video on youtube of 12 hours of white noise. I've used that to break-in my headphones when I'm away from the computer.
Absolutly Yes. Good rule of thumb is 100-300 hours. Depending in the phones. Don't just leave them on 24/7. Give them a break every 4-6 hours.
What Nglazer said. I almost sent back my Sennheiser 650's because they sounded horrible when brand new. Like your Grado's, no bass or highs. Then they just opened up and sound glorious with hours on them.
Give them some time, they'll come around.
My Sennheiser HD800 took a long time to sound their best.
Hi Dmacg

I'm curious. Why the pause every 4-6 hours on headphone break-in? Also does the volume matter? The reason I ask is that during the off hours when I'm not listening I play white noise at a pretty high level on my headphones to break them in. Then when I do listen I turn it down and play at a normal level.
Yeah they do, usually about a minimum of 20 hours playing nonstop at least. But there are a lot better phones out there if you have money, from $700 for the Hifiman HE500 (awesome to me and a bargain) to the $2000 Fostex TH900. It sounds like both of these would suit your taste. Check out head-fi (with a great thread on 50 flagships compared).
Hi Jedinite24;

A few years back in conversation with John Grado about breaking in headphones his suggestion was to use music (choosing something with good dynamic range and across the spectrum from lows to highs), give them a break every 4-6 hours and set the volume a bit higher than your normal high ideal listening level. To be honest, I didn't have the gumption to ask him to explain the whys and wherefors, just thought he knows what he's talking about.
Cheers; dmacg
My HD650 and AKG 702 sounded great from the first day til this day. My Grado SR60 sounded bad from the first day until this day. They are not very good. And they are uncomfortable also. Another high-end legend. Same category as the Sony 5400 entry level Vandys and the Oppo stuff. Does not mean they are all bad, just over hyped. Anointed 'Giant Killers'.
Hi Dmacg

Thanks for sharing again. Wow info straight from John Grado. Very cool. I don't think I would have the gumption to ask him why there should be a 4-6 hour rest between break-in either.
"I didn't have the gumption to ask him to explain the whys and wherefors, just thought he knows what he's talking about.

What a wasted oppourtunity. One of THEM actually stepped down from Mt Olympus to speak with us mortals, and you froze!!! How could you not have asked him!
It was many years ago at an audio show. Maby next time.
Oh, and Jedinite24, What I meant is to give them a break (an hour or two) after 4-6 hours of playing music. I should have been more clear.