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Unsolvable Woofer Pumping (Phono only)

I'm at a loss for trying to find the source of my "woofer pumping."  It's most noteworthy when playing something that is mostly/all treble, and the woofers of my Focal Aria 906s are going nuts (inaudibly, of course).  Turntable is a Debut Carbon with Ortofon 2M Blue.

Initially I was told it's an isolation problem, so I better isolated my TT, even put it right on the concrete floor to test!  Next I thought maybe a problem with the TT itself, so tried a couple others, no change.  So I figured it must be acoustic feedback, as with the TT stopped and stylus on a record, I could produce woofer pumping by tapping on certain parts of my stand...but it is also not this! I turned off my amplifier and recorded from the pre-out to a Tascam digital recorder and played that back afterwards and the pumping STILL happened! So I tried an Schiit Mani phono stage, no change in woofer pumping...I was sure it had to be my pre-amp...

So a local audiophile came over with a couple of pre-amps and we tried those.  The only time the problem went away was when the subsonic filter that one had was engaged.  So, I've ordered some Harrison Labs "FMODs" (20Hz high pass) to see if they will help.  If they do, I may order a KAB RF1 one day...but don't want to spend that much if I don't have to.
Any other ideas on what could cause this?!

tl;dr: Woofer pumping not caused by isolation, acoustic feedback, phono/preamp or a compliance issue...what's happening?!

branden_8091

Showing 1 response by audiorusty

audiorusty
267 posts
 
The fact that a subsonic filter eliminates the woofer pumping indicates that there is an isolation/feedback issue of some sort. Figuring out the sort is the trick. The problem may not be acoustical.

Your cartridge is picking up some low frequency vibrations form somewhere and creating sometype of feedback loop within in itself. A subsonic filter does not eliminate the problem it just keeps the problem from being amplified and sent to your speakers.

Is it possible that there is some electro magnetic interference being created by something not system related or possibly in your power grid that could be causing the problem? Have you tried a power conditioner?

Where's Ralph and Almarg when you need them?
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