I have upgraded the stereo but not sure if the black stripe is negative or positive. It sounds bassy but but not sure if its correct.

Does not matter which one you choose as the positive just be consistent across all speakers, generally black would go to the negative.

If the speaker isnt marked a simple visual test is with a 1.5volt battery with some wires attached to the battery terminals will tell you the polarity. Attaching 1 wire from battery onto a speaker terminal and the other touching on and off will make a tcking sound and push the cone either in or out. If the speaker cone pushes out the positive wire from the battery is the positive terminal on the speaker. See pic.

 

 

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ill try the battery test.

thanks

As twason said as long as all the speakers are done the same way it won't make any difference...

It does make a difference especially if running a sub as the low mids will drop out if the sub is at correct polarity and front/rears are reverse polarity.
Another thins is how would one know if they are all the same polarity if they are not marked on the terminals as some factory speakers are not marked. Also most of the time factory wiring does not have a black and red wire but an array of colour codes with a trace colour (Sometimes black) seperating the positive and negative.
The only way to test phasing by ear is to set fader to the front speakers then set balance to left or right and if the bass drops in centre position and the sound is defused the phasing is out by 180 deg. Do the same for the rears and finally with balance in centre then fade from front to rear checking for loss of bass and defused sound.

I think its alot easier testing first up as described in my first post the polarity is correct the first time.

If as I said before that all the speakers are wired the same then that would include the sub!!! If the wiring doesn't have a trace then you need to test, preferably with the 1.5v battery method!!!

thats how i did it the first time but there was minimal difference in sound thats why i wanted 2 know wat the wire colours were..