Sean: interesting on your Dad's speakers. I also have speakers with a downloaded (or is that uploaded) woofer, and have had excellent results with vibrapods (my speakers are floorstanders that weigh about 45 lbs. each). I have a suspended wood floor with a low pile berber carpet. Here's a suggestion for your Dad: have him buy two pieces of laminated or security glass (very dead and does not ring-two pieces will cost him about $40 max) slightly larger than the footprint of his speakers then go: carpet/glass/pods/speakers. I have had no twisting or leaning issues this way and the speaker will also be less raised off the floor than with his MDF sandwich. For what it's worth, I use a one number higher pod at the front corners of the speakers than I do at the back as most of the weight internally is closer to the front of the speaker.
Ernie: here's a cheap ($25) experiment for you. Play a piece of music at relatively high levels with your speakers spiked. Place your hand on the top of the speaker cabinet. Take the spikes off and put the proper pods under the speakers. Play the same piece of music at the same level/put your hand on top of the speaker cabinet. Presto: Much less vibration! You can bet your life if the cabinet is vibrating, all the drivers are too. In my setup definitely sounds better too.
Ernie: here's a cheap ($25) experiment for you. Play a piece of music at relatively high levels with your speakers spiked. Place your hand on the top of the speaker cabinet. Take the spikes off and put the proper pods under the speakers. Play the same piece of music at the same level/put your hand on top of the speaker cabinet. Presto: Much less vibration! You can bet your life if the cabinet is vibrating, all the drivers are too. In my setup definitely sounds better too.