Down-firing Sub makes floor rattle

marco, i have tried 1 slab of granite, about 1 inch thick, but that still didn't work...what thickness should work? thanks

thanks for the advice. i will try some more things...wouldn't front-firing the sub be better in my case?

1 more thing....the manual says the crossover on sub should be set at 70% of main speakers lowest frequency...so if my speakers go down to 56 hz, the crossover on sub should be set to 39hz...does this make sense? that leaves a huge gap between where mains leave off and sub picks up...i am assuming martin logan knows what they are doing but this doesn't make sense to me....... what do you guys think?

update........lowered the crossover to 39hz, huge difference, sounds much better...also, kept it downfiring, but put the spikes on, also definite improvement...now just trying to fine tune the volume...gonna listen like this for awhile, then try to front fire...see what happens.....i really do like this sub and may just get another for stereo subs...what do you think?

hey, thanks for the info....i am getting very close to getting this sub sounding very, very good with pretty much seamless integration......i have been playing with the phase, which i just thought should be at 0 because the sub is in line between the speakers...while it gives me the most bass, it is not the best bass...i think this has been most of the problem i have been having....i have neen trying 90 and 180......180 degrees seems to be the ticket...all of the problems i have been having are mostly gone....i am now getting good tight, deep, bass, with no overhang...

zephyr, i do like those stands and may look into it