Almost too obvious to mention, but sometimes the obvious is overlooked: Periodically tighten (don't over-tighten) any screws on the exterior of the cabinet! I rebuilt a pair a few years back, listened to them on a regular basis, but never gave them much thought after I set them on their stands. Gradually I was finding them less satisfying, noticing muddiness in the bass, poorer soundstaging, etc, but hadn't gotten around to investigating... It wasn't until a rattle developed on certain bass notes that the lightbulb went on. Every screw had been fully tightened a couple years ago, but between the vibration of the cabinet and the expansion/contraction from temperature every single screw on the driver baskets and the rear connector panel had loosened by at least a half-turn, allowing some air to escape around the caulking. After re-tightening, everything snapped right back into focus: sound staging back, bass no longer muddy! From now on I'll be remembering to include this in my maintenance routine! *Of course, not all speakers will have this problem with fasteners, but mine did. *Be careful not to over-tighten screws, to avoid bending baskets or warping plastic parts. Hopefully someone out there will find this useful.