How to treat a difficult listening room with four dissimilar walls?

[MickeyBoy]

Below is a graphic from REW Room Sim giving an outline of the room seen from above.

The front wall faces a walk-out exterior concrete wall. The back wall is typical finished interior made of sheetrock, likely with no insulation within. There is a door.
The left side wall faces the backyard and is heavily insulated. It has a fairly large window of double pane glass. The right wall separates this room from a typical unfinished basement; there is only a single facing of sheetrock.

If we go from front wall, to left side, to back wall, to right side, there will be declining acoustic losses from solid reflectivity down to virtual acoustical transparency.

This room has always resisted accurate stereo imaging, tilting the balance to the right. A few questions to help me start an empirical journey with better chance for success. I have the newest editions of Everest and Toole.

Why the balance shift toward the nearly transparent right side?

I have a number of large 6ft x 2ft book shelves I could place in various places anywhere. Would their reflections and diffusion be better off in certain locations?

I could buy or make some free standing acoustic panels - gobos. Any type or placement suggestions?

Thanks for any and all comments.

 

[thcdru2k]

None of my rooms are symmetrical, my wife doesn't allow room treatment, and there are difficult reflections from things like patio doors, fireplaces, windows, closets, furniture, and open spaces that I've had to work around. I'm not sure I've completely solved everything myself, but this is the process I've settled on.

I measure L and R separately before and after every change and only change one thing at a time so I know what actually caused the result. A simple balance adjustment usually isn't enough because each speaker interacts with the room differently. For listening tests, I like tracks with a centered mono vocal because image shifts are easier for me to hear. My wife actually has a better ear than I do, so I sometimes ask her to double-check what I'm hearing.

I experiment with speaker placement and toe-in independently for each speaker. Sometimes I end up with asymmetrical toe-in, sometimes I don't. I just keep whatever gives me the most stable phantom center and the best combination of measurements and listening results. Since I can't find spinorama data for my speakers, I'll occasionally swap them left-to-right to see if a tonal difference follows the speaker or stays with the room.

If I see broad tonal differences between channels, I'll use a little per-channel EQ and remeasure. I try not to chase narrow dips. I also accept that the speakers will never measure exactly the same in an asymmetrical room. My goal is a stable center image and acceptable sound.

 

[Cote Dazur]

Looking at your drawing, it would help you get better stereo if you used an equilateral triangle. I would keep the seating position where it is and move the speakers closer until you reached equilateral.
Place the book shelves on the right wall.
Place a carpet between you and the speaker, nothing else. Keep the space behind the speaker free as well, if possible.
Nothing immediately behind you is better.
You should get a balance and deep stereo image with that arrangement.

 

[Keith_W]

If you want to work out why the balance is tilted to the right, take a look at this website which lists acoustic absorption at different frequencies for different construction materials. The table lists different alpha for different materials. If alpha = 0 it is 100% reflective. If alpha = 1 it is 100% absorptive.

Left wall = glass: according to that website, it is 18% absorptive at 125Hz and 0.02% at 4kHz.
Right wall = sheetrock: not directly listed, but I would probably look at one of the plaster or plywood listings and decide which one applies in your case. Some of them seem to match the absorption spectrum of glass, and some of them are more even.

Why the balance shift to the right: ASSUMING both speakers are outputting the same SPL, the reflections are either louder or arriving earlier. We can not assume that your speakers are outputting the same SPL! Sometimes channels in amplifiers go bad, sometimes speakers are manufactured incorrectly, etc. If you don't have a measurement setup (microphone and REW), I would listen to the L and R speakers individually (unplug or mute the unused speaker) and decide if they are the same SPL subjectively. You will need some way to do the switch quickly, preferably instantaneously because of poor auditory memory.

Personally I think that everyone on ASR should own a microphone. It really helps to diagnose audible problems. Without proper measurements, you are flying blind. You don't know the cause, and you might apply the wrong fix. What if it turns out that you have fried your tweeter and you try to fix the problem with room treatment?

 

[Flaesh]

I would listen to the L and R speakers individually

And\or swap the speakers and listen. If there's a problem with the speaker(s)\amp\cables, the balance will shift to the left.
It reminded me of an old real anecdote: a group of audiophiles were listening to a new DAC and they were experiencing varying emotions from the unusual soundstage. Then it turned out that one of the speakers had an inverted tweeter.
Of course, normally all these possible malfunctions should be excluded before discussing the soundstage))

 

[MickeyBoy]

Below is a graphic from REW Room Sim giving an outline of the room seen from above.

View attachment 539441

The front wall faces a walk-out exterior concrete wall. The back wall is typical finished interior made of sheetrock, likely with no insulation within. There is a door.
The left side wall faces the backyard and is heavily insulated. It has a fairly large window of double pane glass. The right wall separates this room from a typical unfinished basement; there is only a single facing of sheetrock.

If we go from front wall, to left side, to back wall, to right side, there will be declining acoustic losses from solid reflectivity down to virtual acoustical transparency.

This room has always resisted accurate stereo imaging, tilting the balance to the right. A few questions to help me start an empirical journey with better chance for success. I have the newest editions of Everest and Toole.

Why the balance shift toward the nearly transparent right side?

I have a number of large 6ft x 2ft book shelves I could place in various places anywhere. Would their reflections and diffusion be better off in certain locations?

I could buy or make some free standing acoustic panels - gobos. Any type or placement suggestions?

Thanks for any and all comments.

Thanks to all for the good suggestions. I am slowly starting to take some measurements, starting with reverb time and redoing Dirac Live. This should give me a number of good measurements. I'm nearly finished with the Everest-Pohlmann Master Handbook of Acoustics, seventh edition. Then go over again Dr Toole's chef-oeuvre. I'll report back in a week or so.

 

[Waveform Fidelity]

Below is a graphic from REW Room Sim giving an outline of the room seen from above.

View attachment 539441

The front wall faces a walk-out exterior concrete wall. The back wall is typical finished interior made of sheetrock, likely with no insulation within. There is a door.
The left side wall faces the backyard and is heavily insulated. It has a fairly large window of double pane glass. The right wall separates this room from a typical unfinished basement; there is only a single facing of sheetrock.

If we go from front wall, to left side, to back wall, to right side, there will be declining acoustic losses from solid reflectivity down to virtual acoustical transparency.

This room has always resisted accurate stereo imaging, tilting the balance to the right. A few questions to help me start an empirical journey with better chance for success. I have the newest editions of Everest and Toole.

Why the balance shift toward the nearly transparent right side?

I have a number of large 6ft x 2ft book shelves I could place in various places anywhere. Would their reflections and diffusion be better off in certain locations?

I could buy or make some free standing acoustic panels - gobos. Any type or placement suggestions?

Thanks for any and all comments.

I would start with making free standing panels and experiment. Try to get panels/make that done have a backing board and set them away from the walls by a few inches. This will maximise absorption. Try to do an RT 60 measurement if you can so you know what your are dealing with.

I have treatment on walls and ceiling. I needed to temporarily remove the wall panels recently (they have been in place for years) and ironically thats when you notice that the sound has changed.

Money spent on acoustic treatment is money well spent - it bring the biggest changes in sound quality.