I would think that if anything the UFW is harder to drive than the MFW driver as the UFW driver is very stiff excursion wise
The suspension has little to do with how hard a speaker is to drive. The impedance curve and the spectral content of the signal used matters much more. From an amplifier's perspective, the UFW-12 is a very easy load to drive, especially between 25-50Hz. With most of these types of amps, at high output the amps are happier as more of the power gets dissipated across the load and not the output devices. It would be more useful to test in an MFW-15 box at moderate level as the small chamber is what likely highlighted this weakness in the amps. There were a few sources of hum which had been noted over time. One was related to the umbilical up to the control panel and its proximity/orientation to the power transformer (a few ways to reduce this). Another was a matter of grounding and ground loop issues, and the third was only loosely documented, but seemed to be a progressive problem as the amp died and was likely related to some of the parts with poor tolerance combined with sensitivity to heat. I am still pursuing a few promising options from different suppliers to insure we'll have a solution sooner than later.
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