Assistance with an odd acoustic phenomenon

[heboil]

Hi guys -

Maybe the title is a little dramatic, and maybe it isn't that "odd", but I have my room set up, wall treatments, Audyssey has been run, speakers are in a good spot to my seating and I get very good imaging. However, my center image in stereo music appears to just be slightly off center to the right (just slightly... but enough that it makes me feel like my MLP is not in the right spot - tested with lost of music and mono music as well). I am including a photo of my room from just behind the seating position. I have also included a rough bird's eye view of my room. To the left of my theater/sofa is a narrow aisle to walk from the back of the room to the seating. Also, directly on the other side of the aisle is a 5" jut out to hide a telepost. I "think" that might be what is making the centered image off-center (again, very slightly).

When I sit forward in the MLP, the centered image snaps into a dead-center focus. When I move my head back 8-12", it just drifts a very slight amount. What do you suggest I do to solve this? Moving my seating is not my first choice (in fact, not a first, second, or third choice). I like the distance I am from the screen, my surrounds are in a good spot based on my seating and the wall treatments are also in a good spot. So, my big "question" is move the speakers closer to my seated position, move them farther apart, move them back closer to the wall etc?

I am 9' from the speakers in my MLP, and the speakers are ~8' apart from each other (the back of the speakers are about 20" from the front wall and about the same from the sides... at least the front with the toe-in). Now, I can move them wherever I need to (within reason), but this is my basement. Under the FR speaker is a floor drain under the carpet and underlay. Because of the slope on the concrete in that area, it isn't so easy to get that speaker level. So moving is not a problem, as long as I have an agenda for the move. Moving it around in a trial-and-error approach is a royal pain just because it can take me 5-10 minutes to level the speaker based on the drain below.

Thoughts? Suggestions? TIA!

 

[Count Arthur]

If you can't move the seating, how about moving the speakers.

Having said that, your seats appear to be at the dead centre of the room, which may not be ideal.

Take a look at this:

 

[sam_adams]

Without knowing anything at all about the room—no measurements or dimensions, from the posted picture, the right speaker appears to be closer to the MLP than the left.

 

[heboil]

The room is 18'2"L x 12'2"W. Ceiling is about 7'. The FR and FL are exactly the same distance from the MLP (within a 1/4"). My ears (when seated) are 12' from the front wall (so 66% of the room length).

 

[Pareto Pragmatic]

Also, directly on the other side of the aisle is a 5" jut out to hide a telepost. I "think" that might be what is making the centered image off-center (again, very slightly).

When I sit forward in the MLP, the centered image snaps into a dead-center focus. When I move my head back 8-12", it just drifts a very slight amount.

Likely it. The problem sounds like it shows up as you get behind the leading edge of the jut. You can try leaning a board in the leading edge at an angle and see if that changes things for better or worse, as a check. A more finished solution can follow. Or you can try bumping the left speaker up 0.5db or a bit more, that could help for normal seating. And obviously moving the seat forward 8" would likely work too. A very slight toe out of the left speaker might also work. Even a slight toe in could work.

I'd move the couch myself, given a known position where there is not a problem so close to where it is now.

It could be something behind you, are there any asymmetries there?

 

[heboil]

Likely it. The problem sounds like it shows up as you get behind the leading edge of the jut. You can try leaning a board in the leading edge at an angle and see if that changes things for better or worse, as a check. A more finished solution can follow. Or you can try bumping the left speaker up 0.5db or a bit more, that could help for normal seating. And obviously moving the seat forward 8" would likely work too. A very slight toe out of the left speaker might also work. Even a slight toe in could work.

I'd move the couch myself, given a known position where there is not a problem so close to where it is now.

It could be something behind you, are there any asymmetries there?

Thanks. Behind the seating is a kallax unit that is lower than the seating. Back wall is shelving with records, Blurays, comics, toys etc. Could be some reflections off the comics at the back? No asymmetries back there.

 

[HarmonicTHD]

I think there is another thread here describing this problem so you might have a look for additional ideas.

Meanwhile make sure that the mic positions were very precisely measured. I usually use one of those laser distance meters. If that doesn’t help check the gains Audyssey sets. If these are off and would explain the off center, just adjust them manually (eg if the image is left, than increase the left channel). ….

 

[DJBonoBobo]

I had problems like this in a room which wasn't a perfect rectangle (i thought it was, but it wasn't). i measured from the walls to the speakers thinking the walls would be parallel and even, but in the end the distance to the LP was not the same.

 

[heboil]

Likely it. The problem sounds like it shows up as you get behind the leading edge of the jut. You can try leaning a board in the leading edge at an angle and see if that changes things for better or worse, as a check. A more finished solution can follow. Or you can try bumping the left speaker up 0.5db or a bit more, that could help for normal seating. And obviously moving the seat forward 8" would likely work too. A very slight toe out of the left speaker might also work. Even a slight toe in could work.

I'd move the couch myself, given a known position where there is not a problem so close to where it is now.

It could be something behind you, are there any asymmetries there?

Wow. I had some unused wide baseboards and positioned them in that little jut as you suggested. It isn't pretty and it certainly doesn't look stable, but after a few minutes of positioning and some painter's tape to hold them up, I played back the same tracks that seemed to be tilting to the right and those tracks snapped 100% to center. I can't scientifically explain what is happening, either before the fix or after, but it seems to have "fixed" it.

So, does that mean I should build some addition onto the wall and if it is good, leave it as it is? Or should I re-run Audessey after I put the fix in place?

 

[Pareto Pragmatic]

Experimentation triumphs again! I'm glad to hear you had success.

So, does that mean I should build some addition onto the wall and if it is good, leave it as it is? Or should I re-run Audessey after I put the fix in place?

I re-run room correction for my AVR any time I change the room. But I usually work on such issues without room correction, then fix them as best I can, then room correct. For you? If this does not create different problems which you might not notice right away, then leave it as is, because the baseboard worked with the current correction in place.

Given what you tried worked, I would just attach a board or drywall in the front corner of the jut and paint. Or just use wood/finish plywood and let it be a wood accent.

You could do the front and back corners and the third side as well, make it look like a hexagonal post that you can see half of. That would be fine in drywall, or wood.

Or you might try hanging an acoustic panel on the jut. It would be off the wall, and should have the same effect, but might stick out a bit too much for foot traffic.

I would also confirm the effect a second time before building. I would make sure that a 45deg angle is right, maybe try a bit steeper and shallower, because if a few degrees off is bad, I would need to be very careful. If a few degrees changes nothing, then I would charge ahead.

Enjoy!

 

[heboil]

Hey everyone -

Dropping in to give an update.

So, the "fix" wasn't entirely a fix. It helped but didn't solve it across all the tracks that were a problem. So then I spent every evening this week moving speakers, re-running the same track over and over and over again listening all over the room, and moving the speakers a mile along the journey (even with the tough-to-level spikes). So, the good news - I think I have fixed the problem. I needed to bring the speakers closer to me. Much closer than they were. I was about 9.5' from the L&R, but now I am just over 8'. This is no longer ideal for HT due to the speakers being closer to the off-center viewers, but selfishly, I watch and listen by myself 65+% of the time.

One thing I neglected to mention in my first post in this thread, was that the center image wasn't ALWAYS pulling to the right. It was, and it wasn't. It depended on the song. I am guessing it was a frequency thing (but again, what do I know?). But moving everything closer to my listening position gave me the centering of the tracks in question. But it didn't JUST solve the centering issue I had on select tracks. It also opened up the soundstage (width and depth). Things sound much better now.

I am still leaving the fix to the jut-out. And, the silver lining here is that I have moved the speaker away from the drain so now leveling on level concrete is a relative breeze.

Here is a pic of where the speakers ended up. You can see a grid of masking tape I was using to keep my speakers close to each other's distance and angle during the experimentation.

Thanks again.

 

[Chrispy]

Adjust levels on the channels until it seems better where you usually are....is the seat back perhaps interfering too?

 

[heboil]

I don't think the back seat is interfering. But, I am losing my mind .

I moved everything, spent hours re-setting everything, and then back to that original track, centered image feels ever so slightly off to the right. I am thinking less than when I started, but still there. When I increase the dB on the LF speaker by .5, 1, or 1.5 dB it seems to snap back to center. The infuriating part is I was moving everything around and testing and retesting without STEREO... just pure direct. But after running Audyssey and coming back and listening to it again, it just seems a touch off.

Speaking of Touch... that is the track I keep listening to (Daft Punk). When Paul Williams is talking, he just seems ever so slightly off to the right. Nina Simone's Feeling Good exhibits the same problem. However, other tracks of Nina don't really exhibit that problem. Mono records and CDs that I test sound perfectly centered, as do many other audiophile-grade vocal tracks. But, my guess was something about the frequencies was playing tricks on my ears with the room.

And, another thing I never mentioned, is my theater is a six inches off-center (to the right)... which is also where the slight pulling on certain tracks is (the right speaker is closer to the side wall than the left speaker is). I should have thought about it and stated that up front, but I have been in the room for 20 years and think of it being perfectly centered, but the room is essentially centered on the ceiling, not the floor/walls (the ceiling is a few inches short from total floor coverage because of a beam).

Now that I am rambling on, should I change up the absorption behind the fronts (on either side of the screen)? Should I opt for diffusion instead? What about diffusion above the panels on the sides? I have tried hanging blankets on the walls above the panels, but that didn't seem to make any perceptible difference to my conundrum.

Sorry about the blathering. And sorry that I thought I had solved it a couple of times only to "discover" it days later again. The silver lining is still there though, as things are sounding better each time I am adjusting.

And a more to scale drawing of my room:

 

[Matt_Holland]

After all that you finally mention your right speaker is closer to the wall than the left speaker. If that’s not the issue then it could be your hearing. Assuming you’ve tested the system with a mono test track with zero room correction and channel calibration, if the image is still pulling to the right with both speakers equal distance from the side walls the I would get your hearing checked.

Nice setup though.