Buy High Pass Filter or KAB RF1?

Chakster, On a purist basis, I would question the use of those AT pneumatic isolators under a loudspeaker, because it seems to me that depending upon weight of speaker and stiffness of the AT feet, the speakers might be free to rock back and forth when driven hard. That results in waste of amplifier energy, as some is lost in order to move the speaker, and distortion, because the signal to the speakers is partially diverted.  I suppose it would be on a case by case basis whether it does anything audibly bad.  Normally, you want the speakers to be anchored rock solid, so all the amplifier energy goes to moving the drivers.

Craigert, Re this last post, define "rumbling".  Are you hearing a noise or are you watching the drivers do a dance, in and out?

Craigert,  Based on one of your posts here, do you seriously plan to put the filter between the phono cables and the phono input of your preamplifier?  If so, that's a no-no, if you care at all about SQ.  If you're bi-amplifying the speakers, do you use an electronic crossover?  And do you have separate amps for bass and treble?  If so, put the filter at the output of the crossover that feeds the bass amplifier. Whatever your set-up, I suggest you avoid putting the active rumble filter directly across the very low voltage output of the cartridge.