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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 helomech

helomech
1,761 posts
 
Whatever you do, don’t get a subsonic filter, unless of course you want to kill good sound.
This is nonsense. I use the cheap DB Systems filters and the loss in fidelity is barely perceptible.

I also discovered that, indeed, "silent" record grooves are not the same.

You discovered that subsonic noise is often cut into the grooves. This is why you're not getting pumping in the runout grooves. I once believed warps were the major culprit. They’re not. It’s usually acoustic feedback and poor album cuts

Read some of the reviews on these:

http://store.acousticsounds.com/d/60042/DB_Systems-DB_Systems_Subsonic_Filter-Turntable_Accessories

At only $20, it can’t hurt to try them. If you like the result, consider investing in the DB-12 or KAB filter.
helomech
1,761 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.
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