You shouldn't have to cut the stock felt at all. Leave the factory felt in place, but use black electrical tape to create the covering with the small notch cut out in the bottom of the tape. Then, place it over the vent. If you're looking for some feedback to see if the mod has changed the sound, you could mount the tape on the outside of the cups, so you can adjust the size of the open a bit. When you're happy with a size, you could then open the cups back up, place the tape over the felt / vent and then a slight bit of glue around the tape to secure it into place for a prolonged period of time.
i did use electrical tape to seal the cup openings before putting the pads. does sticking the pads using tape will also make a difference?
I don't mean it like that, doing the same thing again isn't likely going to change anythign. You probably need to make a change. If you're not getting enough bass, first thing to do is uncover some of the cup vent. And if you are pulling the 003 pads around the baffle, just seal them to the baffle instead using tape or rope caulk, making sure there's no leaks. This will give you much more bass.
Edited by Dyaems - 7/18/12 at 7:54pm