Here's a weird thing, I got 2 of these in for repair today!
Both speakers worked at very low volumes, but any increase and the amp cut out.
Took out both drivers, and both measured around 0.3 ohms.
Clearly the voice coils here have shorted turns, yours have less shorted turns than mine, but even a couple of working turns would be enough to get some sound out of the driver.
The amp will cut out once it exceeds its current limit, it doesn't sense low ohmage.
And yes I have worked on these before, there are lots of them out there and people break them.
My customer claims they were fine before he stored them in the garage for a long time, so maybe the voice coils have corroded into shorted turns.
I will have to cut them open and have a look.
And yes, I also offered up an old 15" driver to check if it would fit, and it does, so it looks like Mackie decided not to go the unobtanium route on alternative drivers and sourced more generic ones.
The SRM models I mentioned are around 12 inch drivers, but not quite.