Technical question re: Dahlquist LP-1

I own aone of these too and so does a friend who asked me the following question..
"I have received a Dahlquist LP-1 crossover and was curious as to the equation
to determine the 3db down-point.
My amplifier has an input impedance of 10K ohms and the freq is 80hz.Can anyone
help me find the correct value and furnish said equation.
Any information is truly apprciated.Thank you."

I have no clue as to how to respond to this...and I probably won't understand the response...but I'll pass it on... Thanks