SSxx - Q. What's the difference between the two two-way parallel loudspeaker switches?

SSxx - Q. What's the difference between the two two-way parallel loudspeaker switches?

Answer:

The two are identical in terms of what they are doing, switching 2 pairs of loudspeakers in parallel, but the terminations on each are different.  The SS20 uses standard screw down terminations, whereas the SS21 offers 4mm binding posts for termination purposes.