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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
rdk777's avatar
rdk777
577 posts
 
I had a very similar issue occurring at higher volumes and and only at the beginning of the track as soon as the needle dropped (before the music played) - the woofer seemed normal once the track started playing. Brand new Stabi R - so it bugged the crap out of me. After much fidgeting, I narrowed it down to my Google Wifi router which was in proximity to the turntable. After moving the Google Wifi to a lower platform on my rack, most of the issue seemed to go away. Loudness on my ARC Ref 2SE is on - there's no other way to listen to it. Any chance you have a router nearby?

Currently, the acoustic feedback (that's what I'm calling it) is 95% better.  HRS suggested that I try replacing the regular feet on my platform with low frequency feet. I just got them today - I'm hoping they'll work.
branden_8091 OP
60 posts
 
@rdk777 Very interesting...I think I've removed everything from the proximity of the TT that may cause that.  Someone told me it could be a dimmer switch on the same circuit.  Turned out to not be that.
Just looked up your ARC Ref 2SE, that's one hell of a phono stage!


lenmc2964's avatar
lenmc2964
240 posts
 
I had the same problem. I have a Rega 3 TT with Exact cartridge like you I tried everything but nothing worked. I even added two subs to my system. I broke down and got the KAB filter and problem solved. I’ve listen with and without the filter and there is no loss of sound quality. Well worth the money. 
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.
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