Please help, obsessive audiophile question

Some good comments above.

A small amount of channel imbalance that varies with volume is quite normal. Most mass produced potentiometers don't track both channels identically and will "wobble" back and forth slightly as the value is altered. If you want to fix this, get ready to install precision built hand assembled stepped attenuators.

The fact that you showed even voltages at the speakers says that the signal amplification chain is working relatively linearly. This leaves only three reasons for the imbalance that you are experiencing.

1) Room loading conditions are causing image shift due to various reflections and cancellations

2) One of your speakers is working differently from the other causing a variance in frequency response / imaging.

3) Both you and your wife have similar hearing disorders.

My guess is that it is probably either 1 and / or 2 with 3 being a WAY distant third. There is a very easy way to narrow this down. As mentioned above, you can try swapping speakers from side to side. If the balance remains tilted in one direction, it is the speaker / room acoustics interphase that is creating the problem. If the image shift reverses itself, you've got a problem with the speakers.

If the speakers are too large to move around and easily position by yourself, you might want to try doing a nearfield measurement using a frequency sweep to verify relatively even output across the audible band. Taking readings further into the room and away from the speakers may confuse the issue by the reflections / cancellations coming into play. Obviously, small variances from one speaker to the other are to be somewhat expected due to non-precision microphone placement from speaker to speaker. Rather than look for huge abberations, which you hopefully won't run into, keep an eye out for specific trends.

Until you can get things straightened out, i see no problem with using the balance control to maintain the proper center image. Just bare in mind that if you are running any tubes in the system, one side is getting more of a work-out than the other. This can be somewhat alleviated by swapping tubes from side to side after a given period of time, etc.... This is not that big of a deal for SS gear, but you could always swap cabling around in order to try and achieve "more even wear" if a long term situation.

If it turns out to be the speaker / room interphase, sound treatment panels can work wonders when properly applied. I just got done doing some major work on my Dad's system / room. I have gotten no less than three phone calls from him in two weeks just for him to say "THANK YOU" for all the work put in and the results achieved. I've still got a ways to go with his system, but now he understands why i always complained about how bad his system sounded, especially in certain aspects of operation. Not only did these efforts get him far better results with more consistent sound, it bought a lot more respect for my opinions and ears from him. Before this, i was just his big-mouthed older son. Now i'm his big-mouthed older son that should have taken care of these problems years ago. I might have done so if he wasn't so "pig-headed". To be honest, i was only able to make the changes that i did because he was away from the house for an extended period of time : ) Sean
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PS... The type of investigative research that you are doing is the first step towards obtaining truly excellent in-room response with great leaps towards transparency and improved sonics. I am glad to read of someone putting forth the time and effort that you are. I just hope you continue down this path as you will not regret it. Nor will your wife, even though you may drive her crazy initially : )

Believe it or not, i've listened to systems and found major problems that the owner's were completely unaware of. One system had a blown midrange driver in one speaker and another system had one of four woofers dead ( two woofers per speaker ). Neither owner was aware of this until i pointed it out. As such, it is quite possible that you could have a driver(s) that is completely dead or "softer" than the one in the other speaker. Someone else i know ran into something similar to your situation and after doing some testing, found that one of the tweeters, even though it was still working, was -3 dB's down from the other tweeter. Needless to say, he was quite shocked to find this out. Sean
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Sorry, i didn't take notice that you had your system posted with pics and that you were running stat's. You have a very clean looking installation.

It is quite possible for one panel to have higher output than the other. Running a mono disc and facing the speakers together won't be of much help if the non-linearity from speaker to speaker varies with frequency. Just as one speaker is louder in a specific frequency range, it might be quieter in another. Depending on how wide the variances are from speaker to speaker, the frequencies involved and the volume that you perform this test at, finding where it nulls might not give you the results that you think.

As a side note, do you sit dead center in the sweet spot? My Father has a tendency to sit off to one side as he finds the corner of the couch to be more comfortable than the middle. Some people wouldn't think twice about something so obvious, so i ended up having to pull the couch over to one side to counter-act this. He knew that he wasn't getting all the imaging and soundstage that he could by sitting off-axis, but he didn't think it was as drastic as it really was. Sean
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Glad that you were able to work things out and come to some type of a conclusion.

Personally, i would not let Martin Logan off the hook without having the problem corrected no matter what. Not only are the speakers not performing correctly in terms of balanced output between them, it is quite possible that one or both is skewing what you are hearing in terms of frequency and transient response. If both speakers respond to the same signal in varying manners, they will excite the nodes in the room differently. This is true due to the non-symmetrical loading characteristics that are present in most rooms.

Given that swapping sides with the speakers helped to balance things out tells me that the speakers are not loading up the same due to variables in the room. Changing the loading conditions changes the nodal points in the room, which will in turn highlight or minimize output in specific regions. The fact that moving the speakers allowed you to achieve proper balance confirms that there is both a problem with the speakers and that the room isn't quite as linear as you think. Believe me, you are NOT alone in this, even with room treatments.

A good test for something like this is to play a slow frequency sweep as can be found in the Ayre Acoustics "Irrational But Efficacious" CD or on the Cardas LP. Sit dead center in the sweet-spot, turn off the lights and listen to the frequency sweep with your eyes closed. In a perfect world, the sound will remain perfectly centered between your speakers if room acoustics / speaker loading are optimal. In the real world, you will hear the image shift from from side to side as frequency varies. The more consistent that the image stays centered, the better your room / speaker interface. My guess is that ANYBODY that puts their system through this test WILL hear the image walking around. At some points, you can literally hear ( it almost seems like you can see & pinpoint ) the image as it moves around the room. In some systems that i've done this in, the sound is literally flying around the room like a helicopter bouncing off the walls. Cool for special effects but horrid as far as audio goes.

Not only will the image walk around, listen to how consistent the volume of the tone remains. My guess is that you'll hear some spots that are "hot" and others that drop out quite noticeably. The nodes and reflections in the room effect every aspect of the sonics that you hear, both in amplitude and in phase. Doing this test will tell you just how non-linear your room / system is in terms of both amplitude linearity and frequency response. Bare in mind that the results are only valid AT YOUR SEATED LISTENING POSITION. If you want to see what i'm talking about in terms of listening position, run the test several times and then scoot over a few feet in either direction. You'll get completely different responses with each move.

Once you've done this in stereo and you're very disappointed, try doing the same test in mono. You'll be amazed at how much smoother the response is, both in terms of amplitude and frequency response. The image will remain centered most of the time and the peaks and dips in amplitude will have evened out quite a bit. This is the type of response ( or even better ) that you're shooting for in stereo mode. All i can say is "good luck" when trying to achieve this : ) Sean
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Geoffkait: Different room acoustics will require different speaker placement for optimum results. Having optimized the speakers for the acoustics of the room with the panels and then pulling the panels will change the entire presentation and in-room frequency response. Therefore, you're suggestion would entail a LOT more work for most installations if trying to keep things on an apples to apples basis. Doing anything less than the above would provide skewed results that aren't worth the time or effort. That's because they would only lead to further confusion in most cases. Sean
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