Ring-Modulated Sound from Vintage 12" Magnavox Driver

[SlunkBoy]

As stated in the title, I'm having issues with a 12" driver salvaged from an old Magnavox hi-fi console. The bass frequencies suffer from a pronounced ring-modulated sound that, while noticeable at full volume, is very prominent at lower volumes. Deep male vocals have a tendency to set it off more than anything else.

I have tried two different known-good amplifiers, a variety of sources, high-impedance drive, and zobel filters - all to no avail. An adjustable second-order active high-pass filter was effective at eliminating the buzz, but at the expense of so much bass content as to render the whole enterprise pointless. I even polished the contacts, thinking that corrosion might have had some sort of intermittent diode effect at low volumes. Additionally, the driver passes a visual inspection with flying colors.

I don't recall this being a problem prior to a recent move, but I didn't have a chance to do enough critical listening beforehand to say definitively that it is a new issue. The only thing I haven't thought to try is rotating the driver, but it doesn't really sound like anything is rubbing.

Has anyone ever encountered a speaker acting as a ring-modulator? To misappropriate a Radiohead lyric, "it's buzzing like a fridge, it's like a detuned radio." Call the Karma Police, indeed.

[DSP_Geek]

Sounds like a few turns of the voice coil have become unglued from the former.