testing

How do the hell do I see if my voltage is dropping below 12 volts or not? When I use a multimeter on DC on the amp it shows negative when the leads are postive to postive and negative to negative but when I reverse postive and negative to negative and postive it's not negative. And it's also...

I'm curious if there has been any real world testing done on Single Voice Coil subs vs Dual voice coils? What is the SPL gain when using 1 coil of a DVC then when using Both coils in parallel? Difference in using 2x4 ohm SVC's in parallel vs 1 DVC same way. Is there any real gain with a DVC...