Proac Response 3.8 stereo imaging is not centered

You can try experimenting with speaker placement.  Even a small difference in location, toe-in etc. can affect imaging.  If you put the speakers at exactly the same spot as your previous pair, the new speakers and old may interact differently with the room and this might be at least part of the problem.  
 
Have you tried listening very carefully to both speakers to confirm that all drivers are working and sounding the same aside from the volume discrepancy?  Put on a mono recording or switch to mono mode to get an identical signal to both channels fot this test.  Now swing balance all the way to one side to the other to confirm that the speakers sound the same.  I am betting that they don’t sound the same.  If any component—a driver, a part in the crossover is off, the sound would change and not just the overall volume. 

It sounds like an out of phase problem. Reverse the positive and negative on the speaker and see if that fixes the problem. It’s a shot in the dark but you have nothin’ to lose givin’ that a try!!

Presumably you have listened to the tweeter, putting your hand over the mid-bass unit that follows jsut to check? Likewise with the top mid-bass unit?

This might help you single out which unit has lower amplitude.

Otherwise (assuming it's not just a phase issue as mentioned above), you'll need the help of a technician. It may just be a bad soldering

Use an SPL meter and measure mono signals.  Measure close to the drivers and do it at relatively low volumes, say 70db.

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!

I think @yogiboy above, is referring to relative phase, not absolute phase. As in, one speaker is wired with the negative cable going to positive terminal, while the other is correctly. 

This will cause the image to be offset, or diffuse, and not focused. 

The test with an SPL meter is good. There are many decent ones you can download on your phone. 

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?

Hi kb3,

You can get drivers for Response 3.8 directly from ProAc, as I did several years ago. The two bottom drivers are identical. I paid around $800 each. In a review in Stereophile, I think they said these drivers were modified for ProAc, so I did not want to buy them on Internet for much less money.    

Once you make a transaction, you can get them in a couple of days. 

I love the speakers, and I hope this helps.

lectronjh50

You should check the capacitors in the crossover, they are the most likely thing to fail apart from the driver itself.  These have to be removed from the circuit to do an actual test.  If you have an ESR meter (equivalent series resistance) you can do an in circuit test that will give you a rough idea if the caps are good.  I know a lot of techs who think an ESR meter is more useful than a capacitance meter, and it is a lot cheaper too.

You can get a 9 volt battery and connect it to the tabs on that midbass driver to see if it moves in or out; if it does, you know the driver is not completely dead.  
 

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.

If you swap speakers and the problem moves, it’s likely the speaker. Crossover components don’t fail very often while a mechanical thing like a driver is far more likely to have an issue. You could go one more step and swap the effected driver only- take one of the working speaker and put in the non working one and see if its better. If it were me I’d find someone to recone both drivers (in both L/R ) and see what happens. (The reason for both is the visuals, the reconed driver may look slightly different (shinier, less dust) and this may drive some people nuts and convince them they sound different. If you recone both at the same time it's like two new drivers.

As long as you’re looking you might try to confirm that the driver in question is an authentic ProAc driver and not a generic replacement.  Does it have the same identification markings as the other drivers?

You could check resistors if one is failing or someone replaced it with wrong value the output could be lacking or too much could cause what you described. That’s the cheapest place to start then film caps. I’m sure your interconnects are all good and connections are good. I would look for bad solder joints in the crossover and binding post. 

Yes, if it is easy to do, the driver swap will confirm that is, or is not the issue.  I hope it is not because drivers can be expensive.  The ideal would be a driver from the manufacturer.  The original driver may be a custom job.  It is quite easy for even the smallest manufacturer with not much of its own R&D capability to specify and get drivers customized.  A local dealer in my area who makes some of his own speakers to sell in the shop, had woofers customized for his requirements.  He specified some of the basic design elements and performance parameters, and the manufacturer built prototypes.  As a retail shop, which builds a somewhat limited number of custom speakers, the minimum order of 40 appeared to be a challenge, but, about two years later, he is ready for another order of 40.  That was it.  Easy.  If ProAc says their driver has been customized, it probably is a genuine claim.

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!

Congrats on finding the issue — must be a relief knowing what it is and that there is a replacement available.  Great idea to go with factory unit just for peace of mind and especially if you might wanna resell them down the road.

I am sure you have tried this however you might reverse the speaker wires, left.to right and right to left just to rule out upstream  issues.

I am sure you have tried this however you might reverse the speaker wires, left.to right and right to left just to rule out upstream  issues.

This is a very good speaker that is very much worth fixing.  A factory supplied driver is the best approach.  Even if an off-the-shelf ScanSpeak driver would work, you will have some lingering doubts that might hurt your ability to enjoy this fine epeaker.

Are the factory replacement drivers available as matched pairs?