Help troubleshooting: 1 speaker is playing significantly lower

Greetings all-

So I connected my Sonus Faber Concertinos and for no apparent reason the left speaker is playing at a significantly lower volume than the right (with no distortion) Fyi- I never drive them hard and I meticulously power down my rig when swapping speakers. I rebooted the rig and same issue. I then swapped the SF with my Vienna Acoustic Hyden’s and they played perfectly. 
I haven’t had time for further troubleshooting, I’m curious as to what possibly could be the issue. Also, if the speaker is shot, where does one turn to for repairing a SF vintage speaker? 

thanks in advance!