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MLP near back wall unavoidable - what to do?

-Matt-

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It seems everything in audio is a compromise.

I guess a pretty common compromise (in normal living rooms, not dedicated listening spaces) is that the main listening position can end up being too close to the rear wall (and can't be moved for whatever reason).

Various Audyssey setup guides call for measurements to be made with the microphone behind the MLP, but also say that the microphone should not be positioned closer than X cm from the rear wall (eg. X is sometimes quoted as 30 or 50). (They also suggest at least 30cm spacing between measurements).

If the MLP is say about 50cm or less from the rear wall it becomes impossible to comply with the mic positioning recommendations - so we can expect Audyssey to perform sub-optimally.

What advice can be offered to those whose listening position is unavoidably close to the rear wall?

Remember, we are talking about living room type spaces, and so room treatments such as huge thick accoustic panels are probably unacceptable. I'm thinking more of things like maybe a notch filter in the bass frequency that corresponds to the distance from the back wall.
 

HarmonicTHD

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It seems everything in audio is a compromise.

I guess a pretty common compromise (in normal living rooms, not dedicated listening spaces) is that the main listening position can end up being too close to the rear wall (and can't be moved for whatever reason).

Various Audyssey setup guides call for measurements to be made with the microphone behind the MLP, but also say that the microphone should not be positioned closer than X cm from the rear wall (eg. X is sometimes quoted as 30 or 50). (They also suggest at least 30cm spacing between measurements).

If the MLP is say about 50cm or less from the rear wall it becomes impossible to comply with the mic positioning recommendations - so we can expect Audyssey to perform sub-optimally.

What advice can be offered to those whose listening position is unavoidably close to the rear wall?

Remember, we are talking about living room type spaces, and so room treatments such as huge thick accoustic panels are probably unacceptable. I'm thinking more of things like maybe a notch filter in the bass frequency that corresponds to the distance from the back wall.
The only thing what you can do, is what you are already doing (unless you change your mind on wall treatment) - EQ it as best as you can eg using Audyssey or REW or a combination of both.

Don’t worry too much about the mic distance. Simply speaking, the 30 to 50cm recommendation comes from the objective to have as large as an optimal listing position as possible (often in home theater you want more than one person to have best sound). If you compromise however use the mic distance for whatever is suitable for your situation. You just end up with a tighter optimal listening position and less averaging, not necessarily bad if kept in reasonable limits eg 20cm also works. You can also skip (or use unchanged position) of the measurements which are behind you if physically impossible. As you said it’s always some compromise of one sort.
 

Doodski

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I used 2- 6' x 3' x 3" acoustic panels behind my head when the sofa was pushed directly against a wall. It worked wonders on the entire room and the imaging was fantastic. The treble was very clear and the mids where really tight and snappy. I don't think you can get that by adjusting your PEQ.
 

StephenMSmith68

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I have this same common situation. Pulling out couch 6" from back wall works wonders as does my 6' x 4' acoustic panel that I made myself.

Ignore the pillows in this pic, I was experimenting w/how Audyssey adjusts if I tried to replicate my body.

PXL_20220603_200028666.jpg
 

DonH56

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FYI: Pillows are not always a real good match to the body's absorption, and setting the mic (or it's tripod) on the couch instead of the floor can corrupt the readings since the couch may vibrate. I usually suggest picking up a cheap boom mic so the tripod (mic stand, could be a heavy circular base) is on the floor and the boom puts the mic where you want it.

I like the other suggestions, mainly moving the couch out a hair if at all possible, and especially putting some absorption behind the listening position to help control reflections from the rear wall. Can't do much for the deep bass, but will help the rest of the frequency range.

Note comb filter/SBIR effects happen at multiples, not just one frequency, so a simple single-frequency notch filter might not help (can be used for the fundamental, perhaps). See e.g. https://www.audiosciencereview.com/forum/index.php?threads/comb-filter-effects.25432/

HTH - Don
 

StephenMSmith68

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FYI: Pillows are not always a real good match to the body's absorption, and setting the mic (or it's tripod) on the couch instead of the floor can corrupt the readings since the couch may vibrate. I usually suggest picking up a cheap boom mic so the tripod (mic stand, could be a heavy circular base) is on the floor and the boom puts the mic where you want it.

I like the other suggestions, mainly moving the couch out a hair if at all possible, and especially putting some absorption behind the listening position to help control reflections from the rear wall. Can't do much for the deep bass, but will help the rest of the frequency range.

Note comb filter/SBIR effects happen at multiples, not just one frequency, so a simple single-frequency notch filter might not help (can be used for the fundamental, perhaps). See e.g. https://www.audiosciencereview.com/forum/index.php?threads/comb-filter-effects.25432/

HTH - Don

Yep, that's exactly what I discovered w/the body pillow experiment -- noticeably subpar results w/XT32.

The other big issue for those of us w/MLP against a back wall is mic height for Audyssey calibrations. For the pic above, I get dramatically different sub levels and delays w/just a couple inches higher or lower.
 
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-Matt-

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Thanks for the replies.

pillows... to replicate my body.
Haha, yes I've tried this too!
(but do now have a boom mic stand)

When I wrote the original post I tried to steer the conversation away from room treatment. I was sort of expecting that to be the default response; unfortunately my wife thinks this will "ruin" the look of the room. It would take a lot of negotiation to get this signed off!

I was hoping there might be some other suggestions.

For example, is there an interplay between rear wall reflections behind the listener and front wall reflections from behind the speakers? I.e. Can improvements be made by adjusting speaker distance from the front wall?

The situation isn't too bad here, the sofa is already pulled away from wall (almost 30cm). My ears at MLP are about 57cm from the rear wall. I have two subs; the main one at the front corner and a second smaller one at the centre of the rear wall, directly behind MLP, to try to fill in any big dips.

Has anyone who has added rear wall absorption panels got before and after measurements showing a good improvement?
 
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-Matt-

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I used 2- 6' x 3' x 3" acoustic panels behind my head when the sofa was pushed directly against a wall. It worked wonders on the entire room and the imaging was fantastic. The treble was very clear and the mids where really tight and snappy. I don't think you can get that by adjusting your PEQ.

What sort of distance did you have from your main speakers in this setup?

I'm sort of resigned to not being able to get good imaging, but I think this has more to do with the main speakers being so far away. I.e. in a long thin isosceles triangle rather than an equilateral.

If I went for a panel it would probably be about 2m x 60cm x 10cm. I'd be hoping for smoothing out of dips and peaks in the bass and improvements in general clarity/inteligibility.

In terms of the clarity part... In REW what metrics are there for this? I've heard of rt60 but never looked into it, would it be relavent to this?
 
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DonH56

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You can buy or make absorption panels with pictures printed on them, textured, in any number of colors, etc. Look at the Kinetics Noise Control site, Real Traps, GIK, or other places for examples of the types of things you can do.
 

Doodski

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What sort of diatance did you have from your main speakers in this setup?
It was a rectangular room, I was placed on the long wall and the speakers where facing me on the other side of the room on the long wall. Dimensions of the room where about 12' x 18' with 8.5' ceilings. The sofa was pushed directly against the rear wall with to 2 panels pressed between the sofa and the wall. The speakers where pulled out from the wall about 1.5 feet and where transmission line cabinets about 4.5 feet tall. So the distance from me to the front of the speakers was about 9 feet. The triangulation was close to a equilateral.
 
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-Matt-

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You can buy or make absorption panels with pictures printed on them, textured, in any number of colors, etc. Look at the Kinetics Noise Control site, Real Traps, GIK, or other places for examples of the types of things you can do.
Thanks, yes, I've been looking - sadly the suggestion of any type of panel is still receiving a very negative reaction.

However, there is still hope, thanks to an even more negative reaction to the alternative idea of moving the sofa further forward!
 

Hipper

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Thanks, yes, I've been looking - sadly the suggestion of any type of panel is still receiving a very negative reaction.

However, there is still hope, thanks to an even more negative reaction to the alternative idea of moving the sofa further forward!
What sort of couch do you have?

A couch with a head rest could help. Or a temporary headrest when listening (temporary acoustic panels could also be placed there then removed when not listening if you want to go down that route). These would all reduce back wall reflections.

In Audyssey is it possible to measure in the listening position (s) only? I use REW and I measure only in the listening position - the head of the mic exactly where my ear (or centre of head between my ears) will be.

Can you move the sofa forward for listening and return for normal use?

I find that it doesn't matter if it's an equilateral or isosceles triangle, as long as you have symmetry for left and right speakers and room.

Reflections act like light rays in a mirror. They mostly concern frequencies above around 250 Hz. These reflections will muddy the sound/imaging. I don't like them and use room treatment to absorb them (some people do like them because they claim it widens the image). The only other way that could help is to sit really close to your speakers so you get mostly direct sound. EQ/DSP doesn't do it. The way to find out if removing them will be beneficial to you is to place some absorbent material (pillow, duvet, blanket) where reflections occur and listen. The side wall is the best place to start.

Reflections off the front wall can come direct from the speakers as the sound seems to bend round the corners of the speakers, hit the front wall and travel to your ears. These 'rays' can also continue past you onto the back wall and reflect towards the front again. Sound direct from the speakers can also go to the back wall and reflect forward. That plus reflections off the side walls will mean your ears will receive a lot of reflections. Whilst some will be added to the direct sound (this requires an understanding of psychoacoustics, in particular the 'precedence effect') some will act like echoes.

Most people live with reflections so it's not the end of the world. Most important is to manage the bass and DSP can do a good job with that.
 
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