If there's one thing I've learned about EPI speakers (I have 7 pairs currently), it's that they MUST be as air tight as possible. I've tried several different remedies for woofer and tweeter gaskets, and I found the thin foam you get at the hardware store for sealing around windows and doors works well. A roll will do quite a few woofers and since it's adhesive only on one side, you can remove and reinstall the woofer again without issue. It also adheres right to the woofer, so there's no repositioning or guessing if it's sealing.
Another thing I've found to additionally help performance, if you want to go even a step further, is working with the damping materials inside the cabinets. I've yet to have a pair of EPI's have the same amount of damping materials in them. What I like to do is remove the damping material from the pair and then divide it up equally between the two. When I reinstall it, I will position it against the interior walls of the cabinet. Since most cabinets are quite under filled, this leaves a large gap in the center of the speaker, behind the woofer and tweeter. I will fill this area with poly fill. It sounds silly, but I will talk into the speaker as I'm adding poly fill. You'll notice a slight echo at first, but as you add poly fill (Do it evenly, not packing it tight, and not leaving any unfilled areas), you'll notice the reverb/echo slowly start to go away. As you fill, you'll get to a point where your voice actually sounds muffled. Stop and begin removing small amounts until the muffling stops but there is no echo. Yep, sounds crazy, but I've done it to 4 of my pairs and it's made a noticeable improvement in sound, especially deeper bass tones. It also seems to add a little more defined punch to the lower mids. At any rate, the cabinets should at least have equal amounts of damping material in them at a proper fill level.
