During a brief trial of a Thorens semi-auto turntable, I discovered that while footfalls didn't cause skipping, they did cause significant woofer pumping on my ported speakers. Which freaked me out, to the point that I returned the turntable. Still haven't replaced it with another one. So here's my question. It's not about whether I could isolate the turntable better--I know I could. It's about whether woofer pumping is anything to worry about. After all, if I'd had the grills on the speakers, I'd have never seen that scary rapid in/out of the woofers, and might be listening in blissfully ignorant contentment to this day. On the other hand, maybe I was right to be concerned. If I can't locate the turntable in a place where it's more isolated, do I need a phono pre-amp that has a rumble filter? Do I need sealed-box speakers that won't pump? Or should I just relax and let the pumping begin?