2. analog
  3. 135607-5312

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?  


Ag insider logo xs@2xo_holter
invictus005
597 posts
 
@atmasphere All of it...
atmasphere's avatar
atmasphere
11,625 posts
 
OK... what do you want to know?
almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
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

Ag insider logo xs@2x
rauliruegas
12,836 posts
 
Dear @o_holter : According your self research looks like the rpoblem is developed by the TT and not a mistmatch between cartridge/tonearm because even at 100hz the Atlat compliance and effective mass puts the resonat frequency in a " solid " 8hz.

The cartridge is a very sensitive " microphone "/transducer and it's picking up " something that is happening somewhere in the TT.

Normally when  a some kind of resonance/vibration are exiting/coincide with the cartridge/ tonearm resonance frequency in between the pick up jumps more than make a noise.

Before you go for the filter try to " figure " what could be happens in your TT. You are the one that know it, even contact the TT manufacturer and ask for its advice.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.
invictus005
597 posts
 
Your problem is most likely a combination of ununiform belt thickness, not precise pulleys, motor rumble, not precise bearing. They all combine and create a mechanical shimmer in the turntable's suspension. 

While playing the runout groove and watching the woofers move in and out. Gently, but firmly place your hands on the plinth and try to very carefully hold it in place. The woofers should move in and out less.
More to discover