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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
raindance
56 posts
 
You need a subsonic filter. In the past many phono stages had them built in with no bypass switch. No idea why they have become optional. 

The pumping is the vertical movements of the cartridge being translated into low freq audio and then being massively boosted by the RIAA Eq. You have a fairly light arm and a high compliance cartridge so it's unlikely to be a cartridge/ arm mismatch. 

If you added speakers with more bass response the pumping would not change. 
joey54
434 posts
 
I had a similar issue with a Pink Triangle turntable using a Moerch tonearm and a Benz Glider. It turned out that my TT was just too close to my speakers. I changed my system layout and the problem disappeared. Good Luck sorting this out.
branden_8091 OP
60 posts
 
@lenmc2964 It seems to have settled down a lot dependent on the record I choose, and my bass settings, but I will still likely consider the rumble filter in the future :)
@raindance I have no idea either, it should really be a no brainer to include IMHO.
@joey54 thanks!
agp46
2 posts
 
branden_8091, let me ask if you have tubes in the phono preamp or elsewhere
glupson
7,842 posts
 
As raindance said (and I implied, too), subsonic filter is what you need. You even mentioned that the issue resolved when you applied subsonic filter. 1+1=2. Now, you can try to figure out why subsonic filter is what you need.
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