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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 5 responses by lewm

lewm
12,537 posts
 
Millercarbon, I don’t say that I’m right and you’re wrong, but I am at opposites to you with respect to all the SR products you mention in your first paragraph or two on tweaks. Not that those things can’t make an audible difference, but I cannot imagine a more profligate way to spend money for what could be very tiny results.And none of those items will address the complaint that brought the OP to this forum.
lewm
12,537 posts
 
Since the advent of small, high power, Class D solid state amplifiers and the rise in popularity of home theater, about 20 or more years ago, there have appeared in the market a myriad of small, self-powered subwoofers that typically also have adjustable crossovers and built-in attenuators (so the output can be balanced with that of the main speaker).  Try a pair with your present speakers, which in my opinion are probably excellent, as I have high regard for Focal.  What you are doing is shifting the "problem" (woofer dancing) from the main speakers to the subwoofers, which you can cross over to at very low frequencies, like 50 or 60 Hz.  The result will be a cleaner sound AND more extended bass.  Anyway, that's what I would do in your situation.  I wouldn't necessarily swap Focal for Harbeth, unless you are truly dissatisfied with the Focals for other unrelated reasons.
lewm
12,537 posts
 
newbee, Good point.  But the cure of damping might worsen the disease.  Damping would add mass to the tonearm, and that would drive the resonant frequency downward.  Resonant frequency is inversely proportional to effective mass.  Oil damping, as you mention, might help if it could be applied to the OP's tonearm.
lewm
12,537 posts
 
No. A speaker with extended bass response would not help. Most cabinets are ported in one way or another and therefore don’t exert much control over the woofer motion. However such designs in my opinion offer a natural sounding bass response. What you’d want is an acoustic suspension type, with a closed box.  The closed box exerts some back pressure on the woofer cone which inhibits the phenomenon you are observing. But in my opinion such types are less natural sounding in the base. That’s just my opinion. By the way, there are several Inexpensive subwoofers on the market that would cost you less money than replacing your entire speaker system. And I agree with others it would help your problem. Many such subwoofers, in order to remain small in physical size, do use some form of acoustic suspension cabinet. That alone would help.
lewm
12,537 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.
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