Removing the cloth inserts that cover the drivers opens up the high end nicely and IMO results in a more balanced sound from the K81DJ. If you don't like it you can just stick 'em back in.
Exactly! With the cloth covering on, the midrange sounds recessed, the treble is muted, and the bass is ridiculously dominant. Removing the covering moves you much closer to a balanced sound, with the midrange becoming more prominent and the treble opening up more. The bass still remains dominant enough to please many a basshead. Finally, if one executes the blue tak mod to cure resonance issues, you should end up with a decent low-priced "fun" phone.