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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
lewm
14,707 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!


yogiboy's avatar
yogiboy
6,203 posts
 
Does that table have a dust cover? If it does you should remove it and see if that helps!
mijostyn's avatar
mijostyn
8,570 posts
 
Branden, this is called rumble. It is worse in your instance because of your speaker's design, little ported woofers. The enclosures are designed to push those little woofers as low as they can go. The end result is that they have to move farther to have any output down low. 
You have two fixes, a rumble filter or using a subwoofer with a high pass filter for the satellites. The subwoofer is a better solution. With a high pass filter on them your speakers will sound MUCH better and you will get better bass with a subwoofer system. Two subs or more will work best. You have to have a high pass filter for this to work. 
mijostyn's avatar
mijostyn
8,570 posts
 
And Branden the low frequency limit is 55 Hz because the woofers are too small to have any significant output below that that you can hear. It does not mean that they do not try to follow the waveform below 55Hz. They will unless you have a low pass filter on them.

Mike
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