Atmasphere OHM generally indicates 6 OHM nominal impedance for their Walsh line speakers.
I have seen measurements and impedance curves on some models that show fairly high impedance >8 ohms over extended ranges with the greatest dip down to almost 4 ohm in the bass region possibly associated with the port.
Users over the years have indicated best results with higher damping amp ratings and I would agree. How high is needed is debatable but I always find the higher the better even if Justas an insurance policy and nothing concrete theoretically to support the need.
If I had to rate them based on what I know and what others report I would say they are moderately tube amp friendly, probably more so than many speakers in their class.
The Dynaudios most likely have lower impedances and are also generally known to not be very tube amp friendly and I would agree. In fact even with SS amps I find results can vary widely with Dynaudios whereas its very hard to find any good quality amp that sounds bad with the OHMs.
Remember also that the OHMs operate totally different than most dynamic speakers ie based on Lincoln Walsh’s transmission line principles. I suspect this may make them very unique in regards to impedance considerations but do not know enough about it technically to say for sure.
I have two OHM models, larger ones with 12" main drivers and smaller with 8". The higher damping in the amps seem to make more difference with the larger models to me than the smaller although I'd say there are audible differences in general with both..
