Do headphones requiere break-in?

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.

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

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.
Cheers