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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 almarg

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almarg
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O_Holter, while it indeed sounds like the problem is a consequence of the arm/cartridge resonant frequency being too low, I’ve been thinking about what might be exciting that resonance, since based on what you’ve said it seems that the excitation is probably unrelated to record warps. And the one thing that occurs to me, 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), is that 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?

Regards,
-- Al

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almarg
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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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