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Why are my woofers pumping?

The other day, with sunlight direct from the side, I noticed that the woofers in my speakers are pumping in and out, much more than I was aware of, when the stylus is in the groove, even between tracks (no music).  I can see it, even if I don’t hear it. Why does it happen? The woofers behave normally (no pumping) with digital music, and when the stylus it lifted from the groove, so it is not the speakers, amps, preamp or phono stage. 

I’ve read that the typical reason for woofer pumping is that the cartridge / arm resonance is too low.  I tested, with my Hifi News test record, and yes, the lateral test puts the resonance at 7 hz or so – too low (but I’ve seen some doubts about the results from that test record).  It is strange, since the combo I use – Lyra Atlas cartridge and  SME V arm (on a Hanss T-30 player) is supposed to work well. I tried to strip my arm of extras, cleaned the damping trough, etc – but it did not help much.

Anyone has an idea, why it happens, or what to do about it?  


Ag insider logo xs@2xo_holter
stereo5's avatar
stereo5
6,424 posts
 
Again, think KAB rumble filter with RCA to XLR adapters.  Problem will be solved with no detrimental effects.
handymann
383 posts
 
O_holter. As I said and agree with CT_0517-I think it acoustical feedback going back into your cartridge. Today I am trying some new phono interconnects and they’re shorter, so I had to take one TT off my “floating” support platform and placed it beside the speaker.  My TT platform is on my left side wall.  Anyway put on Supertramp Crime Of The Century, which is not that bass heavy. No main speaker woofer pumping, but my two JL-Fathom 113’s didn’t like it at all. I was convinced your problem was acoustical, but I read you experienced almost the same problem with cd’s and that it had a rhythm to it like going over a road with expanders in it. Bump...bump... bump...etc. If this is what you’re experiencing, it has to be TT related-except you said you heard it when playing a cd too. My advice-hire an exorcist. Can’t see anyway you can have the sound in both cd and vinyl playing. If only in vinyl, you will probably need a subsonic filter, as I said before. You can always build an isolated floating table, as I did, or buy a TT platform designed for high tech precision instruments at around $5K😳. Please keep me informed. I would like to know what solved your problem, if you find the culprit.
handymann
383 posts
 
Another thought, you may have a bad crossover in your speaker, but that would have to be both speakers failing and that’s very unlikely, but virtually everything you’ve described makes no sense. Don’t get the wrong idea-I believe you, it just doesn’t add up. You’ve invested many hours in posting and trying suggestions.  I feel your pain. Pls try a filter.  If that doesn’t work, you must be in the Twilight Zone.  No disrespect intended. It’s just too crazy.  🙃
handymann
383 posts
 
If you’re hearing a periodic bump and it’s keeps a perfect rhythm, has to be in your transport, except you said it does it on cd too. 🦄
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o_holter OP
977 posts
 
Yes I will tell, once I find the culprit. The subsonic pumping does not occur with CDs, only vinyl. It does occur when I play digital recordings (rips) of my vinyl. Since these were made with zero speaker volume, acoustic feedback is unlikely. As I've said before, my phono preamp needs balanced out, single ended sounds far less good, so the single-ended KAB would need some kind of cludge to work. If KAB had lived next door I would of course have tried it, but it requires ship across the atlantic, tax etc - for what probably degrades the sound even if it takes away rumble.
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