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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
branden_8091 OP
60 posts
 
@millercarbon Thank you!  I've grown up with both, but my earlier systems weren't as high quality (I started at about 6 years old with some crappy BSR changers).  I can understand that a little bit is normal, but this seems a little excessive to me.  At lower volumes I enjoy the extra musicality the comes from turning on the "loudness" function.  I realize many audiophiles scoff at this, but, whatever. I like it.  Since it turns up lower end a fair amount, the woofers really show this problem then.

I have the acrylic platter, but no weight/clamp...I've been meaning to get one and can see how it would improve my situation.  I'll definitely look into a clamp instead of a weight though! Thanks.

Here is a video of the intro to Hotel California, at a normal listening level, loudness on. https://youtu.be/sZG5fL4HwN8


three_easy_payments's avatar
three_easy_payments
2,097 posts
 
It’s sounding like this is probably "normal" performance for this table. With an entry-level table that only weighs 12 lbs, you’re not going to get the performance of a topology that costs more and is focused on design elements such as: high mass in the center of the bearing, incorporation of a low friction bearing, or effective damping that help produce low rumble and smooth operation. I don’t think a clamp is going to help. The KAB will work although many purists feel rumble filters like are sonic bandaids. It just depends on what your goals are and budget you’re willing to spend. It doesn’t sound like you want to spend much if the cost of the KAB is daunting to you.
branden_8091 OP
60 posts
 
@three_easy_payments I see.  I will more likely go the filter route rather than clamp, at least until I get a better system.  If that needs a clamp then no problem.  I do plan on upgrading my system relatively soon, which is why I'm hesitant to spend on a filter I may end up not needing once I've upgraded.  I have another thread on upgrading if you'd like to chime in on that :)
I can't see myself ever having more than a $10 000 system. My current one has cost me about $4000.
lewm
13,264 posts
 
If you do eventually install a high pass (rumble) filter, you might choose a lower frequency roll-off. 10Hz should do it. If your filter has its "knee" at 20Hz, that will affect higher bass frequencies more than is necessary for the effect you desire.

I must say I read your opening remarks, but you went over all the efforts you made rather lightly. At each juncture, I wanted to ask questions. For example, how, after your tapping on the stand caused the woofers to respond, did you rule out an unstable stand as the source of your problem? In the Tascam experiment, are you saying that a recording made from an LP into the Tascam driven by the output of your preamplifier, also induces woofer pumping? What speakers are you using? What is the stated low frequency extension of the speakers? How are they mated to the floor? Carpet or hard surface? Thanks.
branden_8091 OP
60 posts
 
@lewm Sorry about the lack of detail, I didn't want to make it too wordy.  I'm new to forums!  Fair enough about the filter.
I ruled out the unstable stand as the problem by putting the turntable right on the concrete (with thin carpet) floor.  And yes that's what I did for the Tascam recording!...speakers are Focal Aria 906.  It seems (based on all the input I've received here and other forums) that this behaviour is normal for ported, bass reflex speakers such as mine.  Especially with a (in the world of hi-fi) an entry level TT.  I bet if I spent the same on my turntable as I did on speakers I wouldn't have this issue (better bearings, motor isolation, etc.).
The low freq of the speakers on the spec sheet is 55Hz, this is well below that though.  They're both on hard surface with focal stands (which have spikes).
Thank you!


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