I agree that MDF is probably better for home stereo, or permanent theater or PA speakers. Speakers should not add their own colorations, but reproduce the signal coming to them faithfully.

But a working musician has to move on down the road. MDF is not as "roadworthy" as birch ply. A few bumps and first thing you know, corners are knocked off, dents all over the place. Anything screwed into it is likely to pull out a big chunk of MDF when bumped. If they get wet (rain, some *&^#% spills his drink on MY expensive speaker), the material swells.

I have rebuilt speakers for other musicians, copying the original MDF cabinets over in ply. Not ONE has complained of any resonances or such. But all like the sturdier ply cabinets.