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

Showing 1 response by rockvirgo

Thanks to all for the responses. Mike's description of the exponential phenomenon is spot on. I ran some comparisons tonight and the dramatic looking woofer-wubbing occurs only at rock-approved levels or slightly below; equally with the dustcover on, up or off; equally between music cuts or during them; and not at all, regardless of volume setting, with the stylus out of the groove, the platter spinning and the tone arm cued up. The stylus rides flat on the test LP's so I doubt warping is the issue, unless you consider a record groove to be a warp of the vinyl blank.
I never noticed the wubba effect with the grills in place. Though I have new admiration for their wubba hiding properties, I'm leaving them off anyway.
The whole rig's fidelity to the suggested subsonic signature even with no recorded signal present makes me wonder: is subsonic woofer wubbing inherent by nature in the LP playback process?