# Partial wall reflections



## Otto (May 18, 2006)

Well, I created a thread here a while ago about general acoustics, and I'm still working out ideas for treatments. As many of us do, I have a number of other "projects" that are keeping me busy at the moment.

Anyway, frequently, while listening to 2-channel music, I'm bothered by a tendency in my system/room to "pull" me toward the left speaker. Sometimes, sounds that I think should be anchored firmly in the center of the soundstage are smeared toward the left. I have one "audiophile test" track that is to test imaging, and the guy is talking out of the direct center (according to him, anyway), and I can clearly _hear_ him coming out of the left, just enough to be super annoying. All this having been said, my system generally performs very well, and a lot of music _does_ image and stage correctly, with vocals coming from dead center. I have considered the possibilty that, although marked as an "audiophile test CD", the track with the man talking from "center", then "right" and so on, could have something wrong with it.

So, check out the attached image to get an idea for the layout of the room. I have been thinking, for a while, that the "full wall", marked in red, is causing some reverberation, as it's almost directly facing the left speaker. The waves then have an opportunity to bounce back toward the speaker, as well as directly off that wall and toward the listener (indicated by where I've drawn the mess of arrows). This effectively reinforces the sound from the left, while the sound from the right speaker is allowed to go beyond the listener to the far wall, creating much less bounceback and sound reflections from that side.

So, what to do? Cover that whole "full wall", marked in red, with a treatment? I'm definitely going to treat _behind_ both mains, as soon as I can get to it.

I have also considered that the problem could be with any other part of my system. I recently swapped preamps, so I know it's not that. Next step is to swap amplifier channels (EDIT: Swapped amp channels, it's not that), and then speakers, to see if either of those are actually out of spec somewhere.

Am I thinking in the right direction in that the "full wall" is causing me trouble?


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## bpape (Sep 14, 2006)

The non symmetry can definitely be causing the problem. Having the couch right up against the wall is only exaggerating the problem. Is there any way you could rearrange the room to have the speakers up on the North wall of the drawing and the couch out away from the South wall a bit? I think that would help a lot in evening things out.

Bryan


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## Otto (May 18, 2006)

Hi Bryan,

I would love to move the TV to that north wall, but the "box" that's drawn on that wall in the original drawing (not any of the colors I added) is a large five-panel window. If I had a projector w/ roll up screen, I could get away with it, and I've considered it. But for now, with the 52" DLP, I don't have a lot of placement options for it.

Unfortunately, the couch can't move much either (it's actually an L-shape, and pretty large, with the other leg of the couch (the "L") not shown in the picture. It actually takes a turn at the north end of the couch and heads toward that left speaker.

Our previous orientation was much, much worse.

Any recommendations in the mean time?


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## Guest (May 10, 2007)

E:

I blame your couch. I think the end of the "L" is to close to the right speaker and is drawing you off center. Would it be possible to rotate the couch 30 to 45 degrees to balance the accoustic effect that it has on your sound?









You are more than likely still going to have extra reinforcement from the right due to the missing walls on the left side of the room. I still expect better sound field centering if the right speaker is not pointed directly at the end of your sofa.

And, is your diagram mirrored or am I going crazy?

Nick


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## Otto (May 18, 2006)

Hi Nick,

Yeah, I tend to agree about that couch "L" doing some weird stuff with that speaker. But it seems like it would absorb sound, not create it. On the other hand, perhaps it's absorbing bass, making the highs _seem_ more pronounced. Or perhaps it's too stiff and it's reflecting sound back toward the speaker itself and/or the wall behind that speaker. 

I like your idea of rotating the couch, and it give me a good idea that I can do more quickly (that couch is a bear to move!). I'll just remove the "L" segment completely, such that there's no obstruction between me and the speaker at all. I think that would give me a quick and easy way to see if it's a contributor. And I can do it in 1/2 an hour! I will almost certainly try that tonight and see what happens.

Then I swap speakers. I really, really hope it's not my speakers.

You're not crazy -- the diagram is mirrored. I got the layout from the original owner, and thought it would be easier to handle that drawing something myself. I should have just drawn what you did!

Thanks for the ideas. 

Have a good day.


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## Otto (May 18, 2006)

Hi.

I was able to move my couch out of the way of the speakers. I detached the two sections from the "sweet spot" seat. I moved them back about three feet. I also angled the curved part to be at a different angle as I could imagine that it might actually "sweep" or "direct" the sound toward my right ear when seated in the listening position. 

This "problem" continues to bother me. I think I will swap speakers next.

Here are a couple pictures of the actual room in its normal configuration.


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## Guest (Jun 3, 2007)

A question/comment from a newbie: Could the large window be a part of the problem? While windows are normally transparent for low bass, they are reflecting mid and high frequencies. According to your drawing, your listening position is on the reflection path from your left speaker to window to you. This could cause both higher perceived sound volume level from the left speaker and the whole stereo image to be shifted to the left. My listening room has also a big window along one of its sides and I noticed a similar effect. Using an SPL meter I adjust volume level for both speakers to be the same at my listening position but I still perceive more sound coming from the window side. It also feels as if the sound stage was extended into outside my window.


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## Otto (May 18, 2006)

Yeah, could be. Although the picture shows the glass exposed, I normally have a full shade down in front of the glass. It's an accordion type pull down thing. You can't see it at all in the picture; it's hidden inside the valance above the window. It's not really absorbtive, but I think it's better than glass.


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## Guest (Jun 3, 2007)

Well, one way to test it is to remove the windows entirely. This is what I will do this summer, when the weather is good and the neighbors are away :hush:


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