Why are my woofers pumping?

o-holter

if you have addressed the turntable, and your amplifier is not blowing its brains out, then it leaves one thing - acoustic feedback. 
what is under the hard wood floors in your room. Do wood beams run under the floor ?   

I have been thinking: the main culprit is the cart-arm combo's low resonance. But is it? Much is in the blue, since the HFN test record is known to be somewhat problematical (e g dont use it to set antiskating), calculators may be crude and we dont even know the exact cu at 10hz for the Lyra. It is 12 at 100 so MAYBE 18 at 10. Or 20 or 22. These numbers make a difference in the calculators.

The basic idea is that the pumping would stop if I change to a lower compliance cartridge - or to an arm with less effective mass. Then the HFN test would presumably show a resonance at ca 10hz - where we want it.

The Kuzma 4point is three grams more mass than the SME V. It should have even more resonance problems than mine. Yet Michael Fremer declared the 4point/Lyra combo so good he could not get over it. It seems that the Atlas sounds good with more arms than the calculators and test record would suggest.

Ct0517 you are right - i’ve installed two beams in the cellar under the rack - I hammered them into place, a horizontal plank on top of each - it makes a lot of difference - i can jump in front of the player without mistracking. This, and separate el to the system, are among my "no looking back" mods / tweaks.

Have you tried solidifying your support table to the wall with an appropriate piece of wood wedged there??  

Since degree of pumping varies with the LP and repeats precisely with the record's revolution, drive problems probably is not much involved - confirmed by cleaning belts and adjusting the player - no big difference.

This comment really suggests an issue with the turntable despite the belt cleaning (which would not address something like this).