Proac Response 3.8 stereo imaging is not centered

Thanks for all the good suggestions.

Yes, I have covered the speakers to determine if they are working but have not measured with an SPL meter. Will investigate the latter possibility.

I don't think speaker placement is the culprit as the problem moves with the speaker position, i.e. the loud speaker is louder in either position.

I will try the out of phase speaker wire reversal, but f I haven't experienced this with other speakers, then I assume the out of phase miswiring would be internal to the speaker itself. 

Unfortunately I don't have any balance controls on my integrated amp so I can't try this test comparing a mono signal.

I can measure speaker coil resistance and look at the crossover connections. I can also solder but delving into the crossover network and measuring/replacing individual components would be a last resort.

Will report back!

OK, changing the phase had no discernable impact. HOWEVER, it appears the midbass driver is not making noise on the weak side DOH! It was moving with the music (maybe sympathetically given the sound waves inside the enclosure?) and the bass and tweeter were filling in around it but it is noticeably silent.

I checked the connections, cone, surround and spider. All appeared good. I pulled the crossover out and all solder connections were good and couldn't detect any loose parts. Unfortunately everything internal to the speaker from the driver connections to the board connections are soldered.

What is my next step? Unsolder everything and check component values? I can't check speaker resistance as long as it is soldered into the circuit. If everything is intact in the driver assembly can the driver still be faulty? A search online yields no used replacement drivers, but apparently a Scan-Speak 8545-01 is an "improved" replacement. Anyone have any experience with this mid driver replacement in the 3.8?

I contacted the Sound Organization (Proac dealer) who will find out if the original drivers are still available. I'd like to stay original but $800 is a lot of money for one driver! I read the same thing about the Proac drivers being "modified" Scan Speaks but I have my doubts. Guess I'll pull the driver out tomorrow and unsolder it to perform the 9V test and go from there. If the caps on the crossover are electrolytics then they should be replaced anyways, so maybe a crossover overhaul is in my future. Fortunately the PC board is large and simple and the components are discrete and easily removable; the most uncrowded crossover I have ever seen. The components are pretty good quality for a 25 yr old design, with large gauge iron core inductors. Can't tell what caps were used, they appear to be Proac branded. I have requested a schematic form Proac to assist in identifying nominal values.

OK, driver removed. It is original with the ProAc logo on the chassis/basket. Measured across the terminals and got open circuit. 9V battery test is moot if I've got an open circuit voice coil. I confirmed I am able to purchase a factory replacement through ProAc. They claim it is different from the Scan Speak replacement because it has a different chassis. A Scan Speak replacement 18W-8545 is about $225, the factory replacement is $500. Think I will stick with factory to stay as close to original as possible. BTW there was a lot of information on line since the DIY'ers in the early 2000's spent a lot of effort trying to reverse engineer and replicate this speaker. Thank you to all who participated in the dicussion!