Not urban legend at all! Anyone with enough years in speaker restoration will have seen this problem. I have a variation on the sag problem: A friend and I are restoring a pair of Fulton J Modular speakers. The 12" subwoofer drivers face downward, firing into a slot. 30+ years of continuous 1G force has pulled the cones downward by maybe 3/16 of an inch, even when the drivers are held facing "forward" or "upward", resulting in measurable changes to the Fs and Qts, compared to a new old stock driver. And this shift has also reduced the symmetrical Xmax. The cones are still centered properly and there is no voice coil rub. We plan to "exercise" the drivers for a few days on a table top with an amp driving them at high excursion at the free-air resonant frequency (to keep power in the voice coil low). Hopefully this will loosen the spider and pleated-cloth surround and recenter the cone at the mid-point of the excursion range. If not, then scary combinations of heat and amateur chemistry will be attempted. Any advice based on real experience would be appreciated.
Thanks, Brian
Thanks, Brian