Unstable Imaging - Causes?

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

Bob,

Thanks for the help. My question is, if you put one of those panels on the left, did you have to buy/build a stand for them? I'm not sure that would work in my apartment; a panel to the left of my system would make it very hard to get around inside the apartment. I suppose I could always just move the panel into place while listening, then move it when I'm done...

Thanks,

John

Couple of comments, a suggestion, but not necessarily any solutions though. 1) Your original post talked about a shift in the highs to the right. I think this is consistent with your description of your room and speaker placement. I'm a bit confused by your now referencing a drift to the left.

2) Use of a solo piano recorded and played back in stereo is not a good test for judging imaging. Usually they are multi miked and in many recordings the engineers have tried to re-create a life size piano (one that spreads over much of the stage between the speakers) and the dominant sound often is left of center, depending on where the recording mikes were placed and how they were mixed.

If you want to see what happens with high frequencies in your room get some recordings of solo instruments, typically reed instruments. They are much more capable of giving you a pin point center image to judge and hopefully balanced reproduction of room acoustics.

A CD/LP which has been of significant help to me in setting up and evaluating music (not test tones) in my rooms is "Depth of Image" by Opus 3. This was originally one of a series of LP's and is now incorporated into some CD's with additional cuts from other CD's such as Timbre. It is minimally miked, small, medium, and large sized groups and vocals of classical and jazz performed by some Sweds. It has been my touchstone for over 25 years regarding timbre and imaging. Each cut is accompanied by a description of what you should hear, and some of the instruments are very revealing of limitations/faults in your system in the high's such as a recorder and an organ but will also show what your system is doing right. A facinating exercise I think.

BTW, you haven't addressed your set up specifically, but don't forget that ceiling reflectons can be as much of a problem as side wall/floor 1st reflection points and are just as much influenced by toe in the effect of which is much overlooked. You haven't (at least I don't recall) ID'd your speakers, but assuming they are cone speakers here is a suggestion for you (one that initially appears counter intuitive) that is often used by professionals in difficult rooms.

Set your speakers up so that the axis of the speakers cross well in front of your listening chair. For example if you are listening in an equal lateral triangle with your speakers pointed straight ahead you have created a 22 1/2 degree angle. Try toeing in your speaker until you have passed your listening position 22 1/2 degrees and then gradually toe it back towards the listener position until it locks in. You will be changing (minimizing) the effect of lst reflection points on the wall, you will also be changing the effects of the reflections from the ceiling and floor. Give it a try before you spend any time or money making panels, drapes, etc. It's FREE. And you can get used to looking at cross-eyed speakers! :-)