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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?  


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Showing 1 response by browndt

browndt
97 posts
 
I am no expert but I had the same problem with a VPI Prime Signature
and a very sensitive Van den Hul cartridge. I moved the cartridge to my
other VPI Prime Signature (identical) and the problem stopped. Turned out it was a acoustic feedback loop being caused by low level sound waves bouncing off the corner of the room.  VPI turntables are well isolated but the VDH cartridge is very sensitive. So I agree with those who suggest isolating the turntable. That said, some cartridge tonearm
combinations don't work, usually low mass cartridges on high mass arms. 




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