Used the YAPO function and it told me one of my rear right surround speaker was out of phase??? I checked the wiring at the AMP and the speaker and it was OK??? So using a 1.5 volt battery I checked the movement of the voice coil and WOW, it was reversed. Opened up the speaker and found the black and red wires were Reversed. I am the original owner and never opened them up, So this was a factory defect issue. I used these rear book shelf speakers, JBL, for 5 years as my Front speakers before I upgraded my system. We all know what out of phase speakers will do to the sound, but my ears never picked it up!!