I just had an email exchange with a tech from S&P. He said the best way to control the speed of these or any fan of similar design is to use this speed controller:
It's essentially the same as an S&P, except with more options. I've had an email exchange with them too and same story as the S&P as far as speed control is concerned. The nice thing is the fan is prewired and there is a "high/low" switch installed from the factory. Reviews look good as far as I can see.
EDIT: The guy just called me. He's been working with growers and hydro shops in San Francisco putting together a line of fans for our applications. I think it's the best selection I've seen...
I could always pay a guy lol.
