Unstable Imaging - Causes?

OK, I've listened to the Stereophile Test CD 3 and have learned the my room has some major issues with acoustics. I am going to build some acoustic paneling using some 2-inch thick mineral wool, 2 layers, to create a 4-inch thick panel, measuring 2' x 4'. I will make 6 of these; one will be positioned behind the right speaker, a second one will be in a stand, just to the right of the right speaker to catch that first reflection point, two more panels along the back one, and one panel on each side back wall. Here are some pics of my listening room:

http://i166.photobucket.com/albums/u100/jsplice/listeningroom002.jpg
http://i166.photobucket.com/albums/u100/jsplice/listeningroom003.jpg
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http://i166.photobucket.com/albums/u100/jsplice/listeningroom001.jpg

“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.”

I believe that originally, the azimuth was off, causing a shift to the right. I then made an adjustment which now causes things to be centered for the most part, but I’m still getting a feeling that the soundstage is more open on the left. It’s been driving me crazy because it’s hard to adjust azimuth when you haven’t isolated all the issues with room acoustics. But that’s what I’m trying to address now, using CDs which I know are balanced evenly between the channels.

“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.”

That’s very true, and I have noticed that myself. A piano is one of the hardest things for a system to reproduce. The problem that I was noticing was simply that the reverberations of the recording venue seem to be causing the illusion of a shift. The reverberation of fthe left wall in the recording venue sounds stronger than the reverberation on the right; this makes it sound like there has been some kind of shift when notes are played louder, because there is more reverberation in the recording coming from the left.

I have done some experimentation with speak placement. I’ve tried moving them closer together, adjusting the toe in, etc. I’ve been able to get the sound to be a little bit better, but still not perfectly even. My speakers are Paradigm Studio 60 v3’s. They haven’t been as particular about placement as much as other speakers I’ve heard. I will try your suggestion and experiment with toe in even more. I’ll report back this evening with any progress. Thanks.

Stringreen: I may have to consider some drapes. I do, however, have sliding vertical blinds, which I usually leave half open so that the blinds are either perpendicular to the glass, or at an angle. I figured this may help to break up those sound waves, but it doesn’t seem like it does a whole lot.

I have just moved into a new house, and the very same system which sounded pretty good in my old house sounds pretty bad here. I called in an acoutic engineer who did frequency, phase shift, etc tests of my now current room, and advised many things. The right side of the room is almost totally glass leading to the back garden and pool. He told me that lows go through glass as though it wasn't there at all - "did you ever notice how loud a big truck going by the house can be?" Highs however, are reflected from glass. All together, all that glass can play havoc with good sound. You might try some draperies, natural(not artificial) plants, etc. to balance the sound.

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! :-)

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

I have a similar setup, with a wall on the right and an open space on the left. The way I fixed it was to get some GIK panels. I put one on the right wall at the first reflection point. I then took the second one and mirrored it on the left, simulating a first reflection point. That centered and locked in the center image for me.

Good luck,
Bob

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

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

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

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?

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...

One more possibility: detach and clean all the connections in the analog portion of your system. Dirty connectors can lose conductivity in ways which vary with the frequency and amplitude of the musical signal.

That sounds like what your experiencing. We've experienced it too and cleaning our phono cable leads and phono stage inputs solved the problem.

Jwglista: The MMf 5.1 as the bellari are un-familiar to me, anyway here are my thoughts about:

+++++ " The entire soundstage will sound evenly distributed until there is a part in the song with a lot of trebble (i.e. sibilance, cymbals, higher octaves of instruments, etc.) at which point the treble shifts slightly to the right. " +++++

Other than you make exactly what Newbee already posted ( on the VTF subject you could try to set-up at the upper VTF limit of your cartridge specs and obviously that the tonearm is flat leveled. ) ) is to check that the tonearm/headshell wires are connected in right way to the cartridge: red one with red cartridge pin, etc, etc, then check if the RCAs tonearm outputs coincide with those tonearm/headshell wires: red wire with right output signal, white one with left output signal, green one with right ground output, etc, etc.

Other than these could be on a cartridge out of target or something wrong on the Bellari.

Regards and enjoy the music.
Raul.

..an easy way to check for proper azimuth is to use a small mirror (preferably one with the reflective side on the viewing side - a camera repair shop is one place to get such a mirror). Set the mirror on the turntable with the arm resting on the mirror, close one eye... Looking STRAIGHT AND HEAD ON, adjust the headshell to be as perpendicular as possible to the reflection. You're really trying to get the stylus perpenducular, but oft times, its hard to see, and mostly, cartridges are manufactured close enough for you to use the cartridge body as a guide.

A headshell is the unit to which the cartridge is mounted. Some tonearms have detachable headshells, allowing for quick cartridge swaps using mutliple headshells.

-RW-

have you taken care of your first reflections? can you post a pic at your listening position

I am certainly not an expert, but I have noticed profound imaging differences between digital and analogue. Analogue is (for the most part) deeper and more spacious in its effects. It sounds like your room is posing reflections off of surfaces that only the deep analogue imaging gets at. I have noticed this too, betwen my Meridian 24 bit CD and my Linn LP12, both are very good, but sound very very different. If I were you before I spent any $$$ I would simply play around with speaker placement and the furniture in the room, including pictures on the wall (beware of glass!)

From what I've read in the manual for the MMF-5.1, adjusting the azimuth can be a pain. What is a "headshell?" Is that a particular tool for measuring azimuth? Cause I'm wondering how anyone could get it perfect without some kind of tool to tell you if it's out of adjustment...

I'm not saying it *is* azimuth in your case because there are so many variables, but azimuth isn't a bad place to start.

I had a similar problem, and when I got a headshell with azimuth alignment (for a Technics DD TT) and adjusted it, the channel balance and imaging snapped into place.

Well I haven't noticed the issue when listening to CDs, which is why I'm suspecting the TT setup. I will try these suggestions to see if anything helps. Maybe it could be an issue with azimuth?

Thanks

Couple of simple things - perhaps the tweeter on the right side is revealing the effect of reflections from surfaces around the right speaker that are not like the room reflections from the speaker on the left side. The first thing I would do is to simply reverse channels at the amp and see if your highs still shift to the right.

Is your listening position equal distance from each speaker and are you sitting dead center? If not carefully create that condition and see what happens.

You don't mention your electronic's but if you have tubes try reversing channels to insure that you don't have a 'hot' tube on the right side.

If all that is of no effect, time to carefully revisit TT set up issues, VTA, VTF, as well as anti-skate.

Hope that helps a bit.