Driver Testing - reduced output

Remove the driver from the crossover before you can say you tested it.  You could have a bad crossover component, and testing with a battery won't help tell the difference.

Use a multi-meter to measure the resistance across the speaker terminals. Normally, the resistance should measure around 3 to 6 ohms. If both measure exactly the same in this range, it's probably not the crossover and instead a driver issue.

I noticed volume differences between my Proac 3.8's . Ended up replacing all four drivers to correct the problem. Sound Organization had them in stock. I forget how much but I remember they were expensive. It was worth it. 

@cdtd   You do need to completely disconnect the woofer before testing. The battery will tell you if the coil is good, If it pops/moves, you really should still check it with an ohm meter...... I’ve never been inside of this speaker, but I’ve been in many. I don’t know this, but just by appearances, looking at pictures, this driver appears to be an Usher 8945 woofer. I don’t know for sure, but if you need to replace, start looking there.

Thanks for everyones response.

I disconnected the driver and it is dead, no motion no sound.   
Im likely going to replace the mids on both speakers to keep each side balanced.

Hopefully the crossover doesn’t have a fault as well.  

Happy New Year🎊