[Wayner]

I have ported speakers, Dynaco A25XL Modifieds, and have no woofer pumping. 91db efficient to boot. I also have a pair of Paradigm Studio 40v.3s and do not have woofer pumping.

If you have occasional pumping, it probably is from a warp in the record. If you have pumping all the time, your platter is not perpendicular to your platter shaft. In effect, the platter is spinning like a top that's running out of inertia.

Also, expensive turntables are not immune from these kinds of errors (or should I say, manufacturing tolerances). If one were to have access to a digital feeler gauge, you might observe a +/- 3 to 5 thousandths of an inch in deflection, tho I'm not sure how much defection will become audible, but the more, the worse.

Don't feel bad, even hard disc drives' discs are not flat and the suspension (tonearm, if you will) that holds the reader head must have "air foils" built into it so that it can maintain the millionths of an inch gap between reader head and surface, along with a platter that is spinning at 7.5-12,000 RPM.

Wayner

[Wayner]

Of course, there is the other evil gremlin for you belt drive lovers, and that would be sub-sonic noise introduced by the belt or motor.

 

[BaMorin]

Of course, there is the other evil gremlin for you belt drive lovers, and that would be sub-sonic noise introduced by the belt or motor.

 

The 1st fundamental resonance of my BD motor falls in @12.5 hz.........well below audible range
My BD table parked both of my DD tables, due to the background noise the DD motors stuff into the platter. The subsonic filter on my preamp wouldn't address that due to being above 18hz in its first fundamental.

[vinyl_guy]

I've never had a need for one.

Laura