Yeah that’s mostly my understanding (see previous post.) With AC you could mitigate the huge transmission loss you get with direct current, but as you increased the frequency you start to have higher and higher inductance losses in the windings of a DC motor. 60 Hz was too high for those motors. 25 Hz was a trade-off point between internal losses and line losses.
Thank you gentlemen.
I assumed that there would be a FReeper who actually knew the answer.
Two is an unexpected bonus.