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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
mijostyn's avatar
mijostyn
8,224 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
8,224 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
branden_8091 OP
60 posts
 
@yogiboy Yes it has one, I’ve tried removing it, no change. Of course, I always play with it up anyay.
branden_8091 OP
60 posts
 
Mike,
@mijostyn Ahhhh thank you! Little pieces of this puzzle keep coming in. I can’t afford and don’t have the equipment to drive a subwoofer...but would a more full range (i.e. floor standing) speaker be a better choice when I do decide to upgrade next? That entirely makes sense about the frequency limit as well.
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.
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