I thought I understood the basics of speaker wiring, parallel vs series and I was hooking up my speakers, but math is not agreeing with reality. I have two 8 ohm speakers and one 4 ohm. I wired the two 8 ohm speakers in parallel, then tied those to the 4 ohm in series (notice the sign change in the graphic). I expected the total impedance to be 8 ohms, but I measure 2 ohms. What am I missing?