Putting weights on speakers?

I use the same tweeters by the way, and those are phenomenal. :)  It's interesting the woofer is crossed as high as it is.  1 kHz... Hmmmmmmm...

I have to say I'm surprised that helps at all.  Those cabinets being that heavy and the woofer being low to the ground (relatively) I would not think that was an issue.  I'm curious, when they play, can you feel vibration from the top of the woofer cabinet, or the top of the mid/tweeter frame, without the weight?

I'd be interested to know what speakers this works on.

I've always assumed this had to do with the woofer rocking the cabinet back and forth, but didn't think a 150 lb speaker would have this effect. 

OP:  What speakers are you using??