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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

Showing 2 responses by audiotomb

audiotomb's avatar
audiotomb
1,112 posts
 
I had significant woofer pumping

https://forum.audiogon.com/discussions/rumble-issues-see-old-thread-update#1559764

Tried everything

then did the feather test

a light feather should be able to move a tone arm

the bearing in my tonearm wasn't moving vertically

all the movement was the cantilever going up and down creating the woofer pumping
audiotomb's avatar
audiotomb
1,112 posts
 

one thing to try

play a record Try to move your tonearm on the record sideways with a light feather

if the tone arm doesn’t move sideways
chances are the bearing in the tone arm is rigid causing It to not move correctly

if the bearing is locked up
all the up down motion of the cartridge to the record is occurring via the cantilever not the arm bearing

the cantilever going up and down produces woofer pumping



Best wishes
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