Oh, people always ask "What's the easiest way of....". :-)
Sometimes you have to give them the right answer, not the quick fix.

**I agree. Now, you tell me: PRECISELY what is wrong with putting a resistor
in series with an AC fan, to slow it down?

In your answer, you may care to refer to the many thousands of amplifiers,
from dozens of manufacturers, which are so equipped (with series resistors).


Nothing at all.
It was a general comment :-)