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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
krelldog
323 posts
 
I think it was the KAB filter....or something similar to that.

I'm not saying its not a good product....it just didn't work for me.
helomech
1,713 posts
 
@o_holter

It sounds as though your setup adjustments might have reduced some cartidge resonance. I’m thinking that was likely part of the problem.

And in answer to one of your questions, yes, sometimes subsonic noise is actually pressed right into the grooves. It can result from multiple steps of the vinyl manufacturing process. It can also result from warps but that is a problem more often associated with stable balance tonearms, such as some uni-pivots, as their tracking force changes when they traverse the warps.

So there’s many factors that can lead to woofer pumping, but only one ironclad solution: a rumble filter. It will only be a detriment to the sound if that is your expectation. For every one who claims they alter the sound, there’s probably a dozen who claim otherwise.
stereo5's avatar
stereo5
6,430 posts
 
I own the KAB Rumble Filter and I am one of the ones that claim otherwise.  (No change in the sound!)
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rauliruegas
13,103 posts
 
@o_holter : Again:

https://forum.audiogon.com/discussions/why-are-my-woofers-pumping/post?postid=1551771#1551771

With all respect to those gentlemans that insist on the KAB filter or the like please ask you: who of them owns the Atlas or even listen that kind of very high quality performance levels?

Seems to me that no one of them because they are not taking in count what really means: quality level performance at the Atlas levels- They say that with the filter they almost did not listen degradation and this just makes no sense.

R.
almarg's avatar
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almarg
9,670 posts
 
Almarg 4-24-2018
... given the unusual design of the turntable’s drive mechanism (comprising six belts, three of them driven by what is apparently a synchronous motor on one side of the table, and three of them driven at a different height by a similar motor on the other side of the table) ... the platter might be being driven in a slightly uneven and/or not perfectly level manner. Perhaps simply due to the condition of the drive belts differing slightly between the two sides.

And I note from your system description thread that the table appears to be around five years old. Perhaps all that is needed to resolve the problem is a new set of belts?


Cleeds 4-28-2018
That actually sounds very much like a drive problem, such as a bearing issue or bad belt.


Atmasphere 4-30-2018
Boy, that sure sounds like a drive issue to me!

Consider replacing the belts!

Best regards,
-- Al

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