Hello, I am Silvano from Italy.
I have buyed a THRESHOLD SA/3.9e and a THRESHOLD S/350e amps. I have also an AUDIO RESEARCH EC-21 electronic crossover.
What I need is the Input impedance of the SA/3.9e and S/350e to set my EC-21.
I need the value of unbalanced input impedance for calculate the 450Hz cut to my EC21 crossover.
Audio Research suggest to use 30K input impedance as treble amplifier.