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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?  


o_holter
atmasphere's avatar
atmasphere
7,068 posts
 
@o_holter A simple way to decrease the compliance of the cartridge would be to load it. I would try 50-100 ohms and see how that works out.

Its not a sure bet- if you load the cartridge too low, its output will decrease, and in turn you phono preamp noise will be more audible. But its worth a try.

Damping would probably make matters worse; I would run it without damping and remove the little bit that runs in the damping trough to reduce mass, even if its only a little bit.
invictus005
597 posts
 
@atmasphere Huh?
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atmasphere
7,068 posts
 
@invictus005 To which part do you address the 'huh'?
invictus005
597 posts
 
@atmasphere All of it...
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atmasphere
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