History on ohm A's and F's.

I do believe that unlike the current Ohms, the original Ohm Walsh's were bending wave drivers, and the German Physiks DDD is just an update of the original Walsh concept. The "inefficiency" of the original Walsh drivers might be due to other factors.

I think the Ohms were both bending wave and pistonic using a voice coil and foam surround.

Sounds like the drive mechanism for the DDD is different as described by Csommovigo as like "striking a bell", but honestly the exact difference is not clear to me.

The difference in basic operating principle between the DDD driver and the Walsh driver on original Ohm F and As is not apparent to me. The drivers are different sizes and cover different frequency ranges for sure, but both seem to operate similarly in principle in a manner one might chose to describe as pistonic or not...not sure what difference it makes because it appears to be the same. Whether pistonic or not, the bending wave principle for producing the sound appears to be the same.

I would also add the the Walsh portion of the newer Ohm CLS drivers also operate on the same bending wave principle.

That doesn't mean that old Ohm Walsh, newer CLS and GP DDD drivers necessarily sound the same. I am certain that they do not just like three different conventional cone driver designs that operate on the same basic principle sound the same.

Mapman, I could be wrong but, I believe you are mistaken on every count.