In the haste of cleaning up the house for Thanksgiving Day company, my wife set seven LARGE books on top my JBL PB-12. When I demoed my system last night using Jurassic Park III something unusual happened. I went to the part where they're taking off in the plane (towards the beginning of the movie) and it crashes, breaks apart, etc. Then a dinosaur appears and the fun starts. Lots and lots of LOW bass. OK, here's the deal: NOTHING on the walls rattled. Everything sounded "tighter". Crisper, cleaner bass. I've had the NSP1's for a year and a half with absolutely no complaints. Then this 'accidental' occurance. Do I need to stuff my PB12 with polyfil? If so, with what kind and exactly how is it done?