1. Surround the midrange and tweater (woofer and tweeter in a two way) with felt. You can felt the whole front of the speaker, if you like. Cover right up to the surround on the driver....if it moves, don't cover it. If it does not move, cover it. You will get less diffraction and more pure imaging and less bright more focused sound. If the speaker was voiced for the extra diffraction then is could sound slightly dull. You would then have to lower the resistance to the tweeter to bring its level back to flat.
2. Remove the xover from the speaker and place it in a damped box behind the speaker and hardwire all xover connections, including to the drivers. Hardwire directly to the place on the driver where the wire comes from the voice coil...not at the other end of the L tab. Removing the x-over from the speaker box gives much greater clarity and so does hardwiring.....binding posts, be gone...all connectors, be gone!!!
3. Damp the frame on the back of the drivers with constrained layer damping material and the insides of the box with black hole pad 5 or other damping materials. Get rid of any fiberglass...this stuff sucks bigtime...nasty to work with, as well. Use wool behind midranges.
4. If you are making your own speaker or have a two way.....put the tweeter on top of the box, put felt on top of the box and move the tweeter front to rear to find the time align spot (use high frequency sounds like cymbals,etc.). Having the tweeter in space mounted on top of a box gives very open sound. With a two way speaker sometimes it can work to turn the speaker upside down so the woofer will be near the top of the box and near the tweeter that is now mounted on top.
Mods to the Emerald Physics CS-2 speakers and much much more. click here