2. analog
  3. 1033049624

Woofer pumping - what gives?

Some years ago I noticed that regardless of the speakers, cartridge or preamp in the circuit my woofers pump wildly out of control the more I advance the volume while playing an LP. They don't seem to be responding to the musical signal but something else. The sound is fine. My humble rig is a Dual 1219 with a NOS Shure M91ED cartridge. Tapes made from the same LP's do not exhibit this odd behavior. Who knows why woofers look like they're going nuts while playing an LP?
rockvirgo
sean
6,231 posts
 
They were either responding to warps or low frequency information that was well below the point of vented resonance or your phono section was leaking DC voltage. None of those are good situations. Sean
>
sktn77a
41 posts
 
The above answer is correct. The reason you don't see this with the tapes is that they don't go below 20HZ. You are seeing arm/cartridge resonance because the effective mass of your arm is too high for the compliance of your cartridge. This sub-sonic "signal" is actually using up a lot of your amplifier's power reserve. You could reduce this by buying a lower compliance cartridge or, if it doesn't bother you and you don't notice it, just live with it.
jetter
3,058 posts
 
Skn77a, I have the same situation but to a lesser degree. Please explain what you mean by the effective mass of the arm is too high for the compliance of the cartridge. I would like to eliminate this woofer excursion.
Thanks,
aboldor
49 posts
 
Ditto Sean. This is why some (esp. older) integrateds/pre's have a "low freq filter" or something similar (they all are hi-pass filters attenuating the signal from ~ 20 Hz and below). If you're sure your cartridge is OK, maybe your rig has this feature - use it. If not, you may want to add such a filter, although its proper implementation is yet another entire story.
More to discover