Front Wall Treatment for Electrostats

[audio4me]

Is it better to use absorption or diffusion on the front wall behind Martin Logan Electrostats?

 

[Brad225]

Yes.........

Depends on your room.

Mine is 2" thick Owens Corning, a 2" air space and 5 1/2" fiberglass with weird looking diffusers hung in front of them.
You really need to try with and without and a combination of both. Every room is different and everyone likes a different sound.

I would bet more people will say absorption.

Welcome to the group A4M, lots of opinions for you to sort through here. Your the only that needs to like the sound of your system.

 

[Rich]

Either will work well to improve imaging and sound staging. But I have found through extensive testing, in my room and my system, that having the speaker panels about five feet from the front wall (to delay the rear wave reflection) and having well diffusers behind the speakers provides much better sound overall than having absorption back there. The diffusers reduce the sonic energy of the back wave enough to keep it from interfering with imaging, while still allowing that diffuse late-arriving wave to be perceived as increased ambiance. The sound is just not as lively and involving with absorption behind the speakers.

 

[JonFo]

It depends on what you want to achieve.

For a broad, diffuse soundstage, some 2D diffusion on the wall can enhance the sense of width as more energy is arriving from the side walls at different intervals/locations. But dipole cancelation will still be there and cause a dip near 300Hz. So for a pure 2Ch music-only setup, with mostly dry-mixed recordings, this can sound pretty good.
Recordings with a more natural venue ambiance result in a more muddled sound due to the added room ambiance/reflections.
This also tends to help mitigate a bit of the head-in-a-vise sweet spot with an untreated wall, as the rear reflections are not concentrated in one location. But it is still a rather narrow spot as there is still a lot of rear-wave energy competing with the direct sound.

If what you want is precise image localization and the ability to hear deeply into dense mixes, or have precise multichannel / immersive audio soundstages, then mitigating the rearward reflected energy with absorption is important. So for any multichannel setup, I recommend using a lot of absorption to manage the soundfield. Not 100%, but it winds up being a lot.

The other instance when absorption on the front wall is helpful, even for plain 2Ch, is if you are not able to place the ESL speakers out into the room, or toe them in enough. Then a 4" thick absorber, offset a few inches from the wall, placed in the line-of-fire of the rear of the panel helps reduce the comb-filtering and mitigates the dipole cancelation effects. If you then want to regain a bit of the reflected ambiance, small reflective surfaces, angled just so can be added to the surface of the absorber to redirect some energy to the side walls.

After 22 years of continually measuring, tweaking, and tuning a room I custom designed to house a multichannel ESL setup, I now have over a ton of treatments (like I said, a LOT) in the room to enable a cohesive, precise 3D audio bubble when playing Atmos music or movies.

This thread documents the big sidewall treatments project and further links to all the research done in the mid-2000's as we figured out the diffusion vs absorption topic. https://www.martinloganowners.com/threads/room-treatments-–-part-2.6931

And this is the diagram of all the treatments placed in the room:

Recent view of the front of the HT with the Monoliths and the sidewall treatments.

 

[JonFo]

This shot of the rear of the room shows the treatments there, which include 3D diffusion in the center, and 2D abfusion (combo of absorber with a diffuser grate on top) behind the rear speakers to spread the width.
The corners are floor-to-ceiling stacks of RealTraps MondoTraps, along with TriCorners up near the ceiling.

The main row of seating was pulled out for this shot, as it was taken when I recorded the room response for my Smyth Realiser A16 Atmos headphone processor. It shows the MidBass Modules that go just behind the seats.

 

[Leporello]

Is it better to use absorption or diffusion on the front wall behind Martin Logan Electrostats?

I have no practical experience with diffusers, so my answer is theoretical. But a frequently recommended configuration is (or used to be) "live end-dead end" (LEDE), with absorption on one wall and diffusion on the opposite wall. Since absorbing all the energy radiated behind a dipole speaker at all frequencies is tricky and/or expensive, the ideal manifestation of this configuration for ESL's would appear to be live end behind the speakers (the term "front wall" is confusing IMO) and dead end behind the listener.

I have always wanted to try quadratic residue diffusers (QRD), such as made by RPG, behind my speakers. These are designed to optimally randomize the frequencies at which they operate. The problem is, my speakers are about 3 feet in front of a bay window, and I don't want to block the windows, and daylight (I'm not hard core enough for that).

I do know from experience that having a wall close behind the listener is horrible for imaging--particularly with speakers that throw out a highly coherent sound wave that gets specularly reflected, such as ESL's. So to avoid that scenario, I sit at a large opening into another room. The "early" reflections are from at least 10 feet away. This leaves the very live end behind the speakers, which I mitigate somewhat with heavy curtains for absorption. I have lived for many years in flats of that configuration, and have found the arrangement to be the best, having tried many.

What I'd love to try is QRD's that are moveable (like window shutters), transparent (made from Plexiglass) or both. I understand how QRD's work, I have a table saw and dado set, and know how to use them. But so far, this is another one of those projects that requires another specialized tool, a round tuit.

BTW I used to compromise with my SO over speaker placement issues but now that we occupy both flats of the two family that we own I have almost complete freedom.

People have reported that too much absorption behind ESL's can result in a dead sound, but I wouldn't know as I've never seriously tried it.

 

[gvera]

One more vote for diffusers, my solution is way less 'proffesional', the wall behind the speakers has a bookshelf on it, with book placement choosen as to act as a diffuser.
I do have absorvers on the wall behind the listening position, as it is too close to be optimal.

 

[Brad225]

I have no practical experience with diffusers, so my answer is theoretical. But a frequently recommended configuration is (or used to be) "live end-dead end" (LEDE), with absorption on one wall and diffusion on the opposite wall. Since absorbing all the energy radiated behind a dipole speaker at all frequencies is tricky and/or expensive, the ideal manifestation of this configuration for ESL's would appear to be live end behind the speakers (the term "front wall" is confusing IMO) and dead end behind the listener.

I have always wanted to try quadratic residue diffusers (QRD), such as made by RPG, behind my speakers. These are designed to optimally randomize the frequencies at which they operate. The problem is, my speakers are about 3 feet in front of a bay window, and I don't want to block the windows, and daylight (I'm not hard core enough for that).

I do know from experience that having a wall close behind the listener is horrible for imaging--particularly with speakers that throw out a highly coherent sound wave that gets specularly reflected, such as ESL's. So to avoid that scenario, I sit at a large opening into another room. The "early" reflections are from at least 10 feet away. This leaves the very live end behind the speakers, which I mitigate somewhat with heavy curtains for absorption. I have lived for many years in flats of that configuration, and have found the arrangement to be the best, having tried many.

What I'd love to try is QRD's that are moveable (like window shutters), transparent (made from Plexiglass) or both. I understand how QRD's work, I have a table saw and dado set, and know how to use them. But so far, this is another one of those projects that requires another specialized tool, a round tuit.

BTW I used to compromise with my SO over speaker placement issues but now that we occupy both flats of the two family that we own I have almost complete freedom.

People have reported that too much absorption behind ESL's can result in a dead sound, but I wouldn't know as I've never seriously tried it.

The advantage to my diffusers is they are hung from the top of my. absorber panels. I can move them 1/16” at a time if needed.
I can move a panel an listen for a positive change or not instantly.

 

[Bodyslam]

One more vote for diffusion.

My pair is currently in the living room of a log cabin, so the walls behind (and everywhere else) are naturally diffusers. No further room treatments needed. They sound better in this room than in any other room I've had them in, and I've been listening to this pair for over 35 years.

 

[audioxcel]

The best sound I have ever gotten from my speakers ( original Sequels) was in a room where they were about 4-5 feet out from multiple windows with horizontal slat plastic blinds. The blinds acted as diffusers and when I listened to music I had a set adjustment that was best for my room.

I think I am going to hang some blinds using adjustable depth curtain rods on the wall behind the speakers in my current home to see how it works here. It is a fairly cheap experiment to try. And worth a try considering the range of adjustments that are possible. It may not be as pretty as using curtains but it will be a lot cheaper and more flexible.

 

[JonFo]

Since it is hard to visualize reflection patterns by just looking at a speaker when placed into a room, one of the tools that really helps is to use a ray tracing tool to play around with room size, sound-source location vs listener location and amount of absorption present.
This tool Amray - The Raytracing Sketchpad is simple enough to whip up some examples. Here is the config for the first example, just copy paste the contents into the 'Load' dialog

41658681383563<settngs>BEAMTRC<spview>0:0:1<sktchpd>3%$197:98,598:98,598:306,197:306#0:1,1:2,2:3,3:0%)230:269%(457:196%

So using those, we have a sound source (lower left) with an omni pattern of radiation and an absorption coefficient of 0.1 (about avg for a 'bare' wall), listener is in the middle, towards the right of the image. Lots of reflected energy here.

Now, if all we do is crank up the absorption to 0.7, we now lose a bunch of the energy from reflections off the front and side walls. The listener now gets mostly direct sound from the source.

That will result in better localization.

Now, an ML ESL is not an omni radiator, so eliminate the outer rays front and back, but still, this illustrates the general concept.

Adding diffusion will further spread out rays hitting them, so the reflections off the side walls are further spread out and have different arrival times.

 

[Brad225]

That's a great example Jonathan, as usual.

I will say, what you see, is exactly why I started with total absorption and then added diffusion that created the image and staging I was looking to create.

 

[Leporello]

The best sound I have ever gotten from my speakers ( original Sequels) was in a room where they were about 4-5 feet out from multiple windows with horizontal slat plastic blinds. The blinds acted as diffusers and when I listened to music I had a set adjustment that was best for my room.

I think I am going to hang some blinds using adjustable depth curtain rods on the wall behind the speakers in my current home to see how it works here. It is a fairly cheap experiment to try. And worth a try considering the range of adjustments that are possible. It may not be as pretty as using curtains but it will be a lot cheaper and more flexible.

The trouble with blinds is they're periodic. So there will be comb filtering.

 

[Robert D]

The trouble with blinds is they're periodic. So there will be comb filtering.

So when you break up the sound waves, the barriers have to be random to avoid that? I never thought about that.

 

[JonFo]

So when you break up the sound waves, the barriers have to be random to avoid that?

Not so much random, as mathematically calculated variable depth / spacing to get an even frequency distribution. Much more complete explanation here: RealTraps - Diffusor

BTW- Those are the products behind my rear channel Sequels in the pic above.

 

[audioxcel]

The trouble with blinds is they're periodic. So there will be comb filtering.

All I know is that opening and closing the blinds in varying positions had a positive effect in the room with glass behind the speakers. The blinds were 1" vinyl, horizontal slats. I would add an adjustable top support rail to add more adjustability of the effects.

Comb filtering is caused by the arrival of direct sounds and delayed reflected sounds at the listening position.

 

[henryeng]

I am new to ML electrostatic speakers. I just ordered ESL13As. They’ll be in a room that’s 18’ wide with 8’ ceiling. Speakers will be 8’ apart with my LP about 10’ in front of them. Stat panels will be 36” - 40” from the front wall, which is wood paneling. Very reflective. SO…my plan is to use one 2’ x 4’ absorption panel directly behind each stat panel. Is a 2” thick panel enough? Should I use thicker panel? Does it need to be a bit off the wall? Spaced 1” from wall? Or just mounted directly on wall?
BTW, behind my LP I have 35’ of open space with furniture etc so no reflections from the wall behind the LP.
Any thoughts from the experts? I listen to classical music which usually has plenty of reverb and ambience already in the recording.