Step 1: The Quarter Mod
This is the easiest and most benign mod, and can undone by purchasing new pads if it goes wrong or you decide you do not like it. Pads can be found online or can be purchased through Grado. What this mod is is pretty obvious from the pictures-it's a hole in your pads. Cutting this hole, however, offers the second greatest change in sound quality of the mods listed here. Cutting the hole makes the music come across much more clearly- cymbals sound crisper, rim shots have more snap, and kick drums are more percussive. Vocals also sound more natural, with everything in general sounding more airy and open. If you find Grados to be too bright, I would recommend doing this mod along with the venting and dampening mod. If you find the balance fine, then you could get away with doing this mod as a stand alone mod.
The same basic results of this mod can be achieved by purchasing Grado 'bowl' pads, which have a hole in the center anyway and offer more of an around-ear fit. But that costs money. The point of these mods are to use what we have to make the Grados even better.
And on another note- Don't cut too large of a hole in the pad. Too large and there won't be enough cushion between your ear and can, and the headphone will be uncomfortable.
The steps are pretty simple. You will need:
3/4" socket or quarter (This is why its called the quarter mod)
1)Remove the pads from your headphone
2) Place the socket or quarter in the center of the back of the pad and press down hard
3) Cut around the circumference of the socket
And that's it....
Remove the circle you just cut from the pad and save it. It is going to be used later on for the dampening mod.
Now just reinstall the pad on your Grados and enjoy!