I bought a 610 cab not knowing what the heck it was, I finally opened up the back, it's a yamaha. Now the speakers are all 8 ohms and say 30w on them. The cab is 4 ohms. What is the power handling for this? And could you show me how the equation works so I can do it myself in the future? I know it isn't rated at 180w because I've been running it at 350 no problem.