Is there a way of setting gains of a 4 channel amp with a multimeter? I want to acheive EXACTLY the same gain for each side after i have bridged it into 2 channels.
I thought testing the voltage of each speaker terminal using a test tone would work but i get very different results from each of the 2 bridged channels.

Also when i test the speaker terminal voltage one speaker terminal reads negative voltage when i have read test lead on + and black test lead on - , does this mean my amp has a polarity isssue?

What tests can be done with a multimeter with respect to car audio? (bridged amp gains?, voltage drop etc)
And in particular what tests can be done to help SQ?

you should set the gain with the speakers disconnected.

and use a test tone, e.g. for subs, around 50Hz or less.

you should have the meter on AC volts, not DC volts.

there is no + or - on AC