And... here's the moment you've been waiting for: [COLOR=B22222]
a real way to noticeably reduce the treble of the DT770[/COLOR] (and may also apply to many other headphones).
What you'll need:
Bounty Paper Towel. Specifically, this kind:
http://www.amazon.com/Bounty-Paper-Towels-Prints-Count/dp/B00I4F1W78/ref=sr_1_2?ie=UTF8&qid=1428367432&sr=8-2&keywords=bounty+paper+towel
(note: it has to be exactly this kind. No other kind of napkin or tissue I have tried would work)
Felt: (any color is fine)
http://www.amazon.com/Darice-FLT-0499-Felties-Sticky-Primary/dp/B004N5L1ZQ/ref=sr_1_2?ie=UTF8&qid=1428367542&sr=8-2&keywords=felt
Shelf liner: (any color is fine)
http://www.amazon.com/Duck-1100731-Non-Adhesive-12-Inch-20-Feet/dp/B002AS9NAI/ref=sr_1_1?s=home-garden&ie=UTF8&qid=1428368182&sr=1-1&keywords=shelf+liner
All of those can be gotten for cheap, so I'd recommend group buy or something like that to reduce cost if you have to order from Amazon. Bounty is probably already in many American households.
Instructions:
Open your DT770 up and remove the retaining thing, then remove the foam piece covering the driver to reveal this papery surface:
Cut out some circular pads of the Bounty paper towels, then lay them over the driver like this: (my DT770 needed 3 layers, but yours may need less)
Then put one layer of felt on top:
And finally, put one layer of the shelf-liner I mentioned:
Then... close the headphone up and enjoy!
Measurement of frequency response before and after:
Notice how treble from 6KHz and above dropped almost 10dB. This made the DT770 much more linear to me. Bass also seems to have increased slightly.