Billy, grasp the headband and push in with your thumbs (on the outside of the band, of course), bend until they loosen up enough to fit well. It'll take a good bit of force but they seem to be quite well made, so I wouldn't worry about breaking them. Or, you can just stick them on a bowling ball for a week, that works too.
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For the Mikros 90 mod you'll need:
a precision Phillips screwdriver
(2)
cotton facial pads
scissors
x-acto knife (or similar)
small amount of blue tack or putty
glue stick
a beer
1. Disconnect headphone cable.
2. Remove earpads, they pull right off.
3. Starting with the right side, remove the 3 screws holding the baffle to the cup. (Put the screws in a safe place, don't lose them!)
4. Carefully lift baffle and metal ring away from cup, don't break the wires going to the driver
5. On the back of the baffle, locate the center, there you'll find a small cellulose dot ~2mm wide. Using the x-acto knife carefully remove that dot, then stick it somewhere on the back of the baffle (just in case you ever need it again)
6. Inspect the small hole that was under the dot, that's the driver's lone bass port. What you'll want to do is to cover 2/3rds of that hole with a very small amount of tack or putty, if you want more bass you can cover it 1/2 way, but to me 2/3rds coverage sounded the most balanced.
7. Inspect the inside of the cup, you'll see there are 3 standoffs where the baffle mounts on to the cup. Using the scissors, cut 3 slits in a cotton pad that match to the standoffs in the cup, each slit will be ~1/4" long.
8. Thoroughly apply glue from glue stick to the back of the cotton pad, then while aligning the cut-outs you made for the standoffs, attach the cotton pad to the back of the cup. Mind the tiny speaker wires, be careful not to damage them.
9. Carefully place baffle and metal ring back on to the cup, aligning the screw holes with the standoffs. This may seem a little tricky the first time, just be patient. Again, mind the cable going to the speaker.
10. Reattach the baffle and metal ring to the cup with the 3 screws you previously removed.
11. For the left side, repeat the same steps as with the right side. In the left cup, however, you'll see a small PCB for the cable jack (be careful with those wires), you'll want to cut a little more of the cotton pad to fit around the cable jack PCB, but otherwise it's the same process as the right side.
12. Reattach earpads.
13. Pop open beer and enjoy the headphones with your favorite music.