Yamaha Stagepass 500 with powered Sub?

Yep, very clear why that didn’t work. You are trying to power the subwoofer with a line level signal on a port designed to take loudspeaker level input.

Only one correct way to hook it up:

• Stagepass monitor output (1/4″ Jack to XLR male) to input on the JBL (doesn’t matter which one, they are linked). Be sure to use the monitor control knob on your Stagepass to set the subwoofer level (just turn up the level knob on the JBL to 0dB or when in doubt to max).

That should do the trick.

Greetinx,
C.