Unstable Imaging - Causes?

Well thanks for the all the suggestions, but I still don't seem to have things exactly right. I tried playing with the azimuth, which seemed to help, but it is very difficult to accurately adjust on the MMF-5.1. I also tried increasing the VTF per Raul's suggestion, which didn't seem to help with the imaging. As for the mirror thing suggested by Stringring, I did try that but used the little mirror on the back of my stylus brush; I have it to a point now where to the naked eye, it looks very straight. But who knows if it's exactly correct. I also tried switching from the Bellari VP129 back to my NAD T162 preamp with built-in phono stage. The sound was much more sterile and congested, but the imaging problem seemed to be lessened. I later realized that this is probably just because it was masking the issue, because I could still faintly hear the shifts.

I've noticed that a lot of the imaging shifts also occur when trying to reproduce the room reflections of the recording venue. The unstable imaging becomes most audible when listening to room reverb and those room reflections.

Could all of this simply be the result of owning a budget turntable/tonearm/cart? I've been considering buying a test record, preferably from e-bay because new copies seem to cost a lot...

Does this high frequency shift mainly on loud levels? If so it is entirely possible that your cartridge or the combo of it and the arm is causing a mistracking which causes, for some ellusive reason I can't comprehend, some uneven and excessive highs in one channel OR a reduction in the highs in the other channel which might well cause the same effect. I think getting a test disc (at what ever cost - so long as it is of value) is a far better idea than just getting higher quality TT's, arms, and cartridges, even though I suspect that maybe where you end up.

Forgive me for being redundant, but have you ruled out speakers and speaker placement as being an issue by at least reversing cables at the phono so the distortions which now appear on the right channel will appear in the left channel if the problem is associated with your TT set up?

As suggested by Newbee, swap the tonearm cables into your preamp and see if the imaging imbalance shifts to the other channel. If it does shift, that could suggest its a hardware problem or a speaker alignment issue. If it does shift, fiddle with speaker position (toe-in or move one slightly forward or back.) If it does not shift, it could be a TT/cartridge issue, but I'd also look to possible acoustic issues in your room as suggest by Wwshull. If the latter, read on.

If one has stable/symmetrical imaging to start with, its not that hard to cause anomolies at various frequencies by introducing or changing reflective or absorbtive surfaces in the room. Walls jutting out, furniture, ceilings - all sorts of things - could be a cause of a certain range of reflected frequencies stacking up in phase with those coming directly from the speakers - sometimes called a comb filter (iirc). The result can be an over emphasis on sounds in a particular frequency range and that can cause the perception of an image shift.

You can find first reflection points by sitting in the listening position and have someone move a mirror along the side walls. Mark the spots where you see the tweeter of
a speaker in the mirror - typically there can be two spots on each side wall, one for each speaker. Lay 2-4 bath towels on top of one another and drape that over a big piece of cardboard (or something to hold the towels in place.) Towels should absorb the highs much more so than the lows. Position them to cover the reflection points marked on the walls and listen again. Ideally you'd do this on both sides of the room at the same time. Try moving the towels around the room, including behind your listening position if possible. If the area to the side of one speaker is open and the other speaker has a wall beside it, try putting the towels on the wall to match the open area on the opposite side. You should be able to modulate the imaging in this way - look for the spot where the imbalance you're hearing goes away.

Tim

Newbee:

Yes, the frequency shift does seem to happen during higher frequencies. I think I have narrowed the problem down to TT setup, because I played with the azimuth some more yesterday and was able to improve the imaging. To the naked eye, the azimuth appeared to be good, but since the channel balance still seemed to be favoring the left, I rotated the tonearm ever so slightly in the counter-clockwise direction, which moved things a little more towards the center. While it sounds better, it still isn’t perfect. When the channel used to be REALLY bad, I did swap the RCA cables to reverse the channels, and the problem was then reversed; this is what led me to believe that it was a TT setup issue, and not a speaker placement or room reflection issue.

Tim:

Those are all good suggestions. I may try all of that just for the heck of it, because I do need to work on my room acoustics. It may make a difference, and is pretty easy to try.

I’ve noticed that the hardest instrument to reproduce evenly between the channels is the piano. It seems that if the azimuth is even slightly off, the reverberation that is heard off the side/back wall of the recording venue may sound louder than the sound coming from the actual instrument in the middle, perhaps giving the illusion that there is a channel imbalance. That’s just one of my theories.

John

Ok well I think I may have narrowed it down here after doing a lot of experimentation. I started listening to some classical piano CDs just to make a comparison on how they imaged compared to LPs. My initial suspicions were correct: the "shift" is caused by an unequal reverberation in both channels, which is favoring the left. The reverberation is heard more in the left than the right, giving the illusion of a shift. I think this may be related to my room. To the left of my setup is a wide open dining room, but the right side of my system is about 3-4 feet from a wall and sliding glass doors that lead to the back patio. It seems as though the wide open space on the left is giving the soundstage room to "breath", whereas it is more confined on the right. This is causing the soundstage to sound stronger in the left. Has anyone else experienced this problem and know how to remedy it?

Thanks