Acoustic Treatments for Magnepans/Dipoles - Diffusion not Absorption

I have spent about a year and half playing around with the positioning of my Maggie 20.7’ in my living room and the acoustical treatments that have seemed to help the sound-stage the best. I am going to share what I have learned through an iterative process of trying a variety of acoustic treatment strategies. I hope other folks will share their experience and pictures of how they treat their room with a dipole/planar speaker that creates a wave form like the Maggies. I have found that the treatment that works for my Magnapan 20.7’s is much different than the treatments I used with my previous dynamic cone speakers. This makes sense as the wave form is much different with these speakers.

I have found that at least in my room there are three basic rules with respect to treating the Maggies:

Rule 1: Treat any bass issue (this is probably also true for dynamic/cone speakers as well). The need to treat bass nodes and bass buildup will depend upon the size of your room and if you are using subs. This was the costliest treatment endeavor for me as I have found that I needed to use a variety of tube traps and sub traps to clean up the bass. If I could have a room that just had tube traps all around the perimeter I would, but I don’t want my living room with a perimeter of columns around the room. The tube traps can provide both bass absorption and diffusion of the mid-range and treble all in one solution.

Rule 2: Diffuse the back wave of the treble and mid panels before they hit the side and/or front wall. Depending upon the orientation of your speaker, your mid and treble wave form is going to hit either the side wall or the front wall or both. Find a way to diffuse these wave forms before you have a second poorly timed wave form coming bouncing of the front wall and hitting your face at the wrong time. This can be a relatively cheap endeavor depending upon your room and your desire.

Rule 3: Diffuse the 1st front wave of the treble and mids behind your head. Find a way to diffuse the front wave launch after it passes your head. You want to avoid having the front wave bounce of the back wall undiffused.

Here is how I addressed these rules in my listening area. My listening area is my living room/kitchen great room that is 18 ft wide by 30 ft long by 8 ft high. It is not a dedicate listening room so I need to have a modular set up as much as possible so I can remove treatments when needed. If I had a dedicated listening room I would go with various tube traps around the perimeter of the room.

Background Listening Mode
The following is a picture of my living room during background listening mode when I am having non-audiophile guests over. Yes, look at all that horrendous reflecting glass. Fortunately, the speaker’s orientation in ideal listening mode is not directed to the glass but the sidewalls. Also, there are relatively easy ways to add diffusion of the back wave before it can get to the glass.

I try to make the place look as normal as possible with speakers the size of Lebron James. Not saying it looks normal, but it is the best I can do. My two subs act as coffee tables to the chairs that hide most of the stereo rack. In this position the speakers are about 6 ft from the front wall and the side treble panels are about 6 inches from the sidewall. The soundstage is wide but not as deep as it could be, and the soundstage is not as precise as when I have my ideal serious listening set up.

All the acoustic treatments are buried behind the speakers and stacked in the corners to treat bass issues and diffuse the back wave of the treble and midrange at least partially. I am getting rid of my murphy bed so I can put some of this stuff in a closet in the near future.

This is what the back wall looks like during background listening mode. My kitchen and back wall have a lot of hard surfaces that can reflect the back-wave sound to my ideal listening position.

Serious Listening Mode:
It takes me about 5 minutes to transform the room from normal mode to serious listening mode. I move the speakers about 10 ft from the front wall with the treble ribbon on the outside. The treble panel sits about 3 ft from the side wall. My listening chair is about 11 ft from each speaker. I move the subs forward to the sides of the speakers and lift them up on the subtraps. I also move the chairs from the front of the stereo to the side wall. My listening chair sits about 10 ft from the back wall or about 2/3 of the way into the room. The treble panel is directed to go about 3 inches outside of each ear. I move the chairs lift the chair up on concrete blocks so I can have my ears at the middle of the height of the panels.

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I reorganize and reorient the treatment tools into their ideal spots behind the speakers to deal with Rules #1 treat the bass, and Rule #2 diffuse the mid and treble back wave. Below I will show a variety of configurations behind the speakers.

1(a) Concrete Forming Tubes for diffusing the back wave

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The speakers are oriented such that the treble panel hits the sidewall and the mid-range panel is directed to the two tube traps in the corner. The corner traps are oriented, so the diffusion portion of the trap is directed towards the Maggie panels. One of the tube traps is placed on the side wall oriented to the side of the sub to handle a node formed by the sub on the sidewall.

Ironically, the cheap concrete forming tubes painted black and filled with insulation to prevent any tube ringing are the most flexible of the diffusion tools for the mid and treble diffusion. They can be moved easily to shape the sound and diffusion from the back of the Maggie panel. I can set them up so they cover the treble and mid-range waves before they hit the glass. They work just as well as the diffusion products that follow. They just kind of look crappy but they do look good buried in a closet or behind a panel.

1(b) Using GIK PolyFuser for Diffusing the Back Wave

The GIK PolyFuser can be mounted on the wall or I just set it on a couple of tubes to lift it to the correct height. It also can fit on the alcove next a couple of feet inside the tube trap to provide some diffusion in front of the glass. I find my ideal set up so far uses a combination of the Polyfuser on the alcove and the concrete forming tubes behind the speaker near the wall.

(2) GIK Gridfuser for diffusing the back wave


The GIK Gridfusers are super lightweight and are easy to move. They also can be painted with water-based paints. GIK has fancier looking diffusers. I tried these because I knew they are easy to move and can be placed in a variety of diffusion areas. You could literally tape these to a wall. They are actually designed to fit in ceiling grids.

(3)DECWARE Diffusers for diffusing the back wave


These are heavy wood diffusers that can be stained or painted. They look the best out of all the diffusing tools. Ideally, they would be mounted on the wall at a height the matched the panels mid spot. I prefer to avoid a permanent attachment to the wall. That is why I prefer the concrete forming tubes in this location.

How to Address Rule 3: Using Concrete Forming Tubes to Address the Front Wave Bouncing off the Back Wall


Yeah. I know this looks like a gong show. I don’t go this extreme often. I don’t have a dedicated listening room so I need to find a quick way to treat the back wall without taking up a bunch of space, which leads to using concrete forming tubes. I can easily move them so they can form a cocoon of diffusion to protect my listening spot from straight line reflections. The forming tubes can nest neatly within each other so I can store them away relatively easily.

Notice the concrete blocks lifting the chair so my ears are at the mid-level panel of the speakers. Try this folk, it will surprise you.

Nesting 4 of the tubes for easy storage.

This is another way of treating the back-wall wave of mids and treble. The nested concrete tubes are easier to set up and store away than this set up.

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This is a list of the products that I have tried. Not endorsing any of them or getting paid anything for this. Just trying to help folks out.

  1. Tube Traps – I ended up using IsoThermal Tube Traps from ASC https://www.acousticsciences.com/products/isothermal-tubetrap

  2. Sub Traps- I placed my two subs on 18 inch by 18 inch sub traps from ASC to help tighten up and eliminate the bass nodes. These things make a big difference and help deal with the vertical room nodes. If you have subs find a solid table and lift them off the ground to test this out. Just lifting your sub will help with vertical room nodes. https://www.acousticsciences.com/products/subtrap

  3. Diffusion Panels – you can find a variety of diffusion panels on the market that are made at various depths, sizes, and materials.
    a. Decware wooden diffusion panels. https://www.decware.com/p1324.htm
    b. GIK GridFuser - https://www.gikacoustics.com/product/gik-acoustics-gridfusor/?v=7516fd43adaa

  4. Polycyndrical Diffusion Panels – I liked these more than the square diffusers. You need to use them at least 6 to 8 ft from your listening spot. I think they are a good value.
    a. GIK PolyFuser - https://www.gikacoustics.com/product/evolution-polyfusor-diffusor-absorber-bass-trap/?v=7516fd43adaa

  5. Concrete Forming Tubes (potentially filled with insulation). – any big box hardware store. 8 to 10 inch diameters are the best for diffusing mids and treble. The cheapest and most flexible way to diffuse your Maggies.

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This is a photo from the testing lab at Audio Research. They use 20.7 Maggies in a relatively small room.
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Many thanks to you for taking your time to share your treatment experience with us. I found your post very informative and a definite learning experience. Pictures to demonstrate your treatments really made a very helpful difference for me.
Chas

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WOW, fats, that is some extreme dedication. Love it.

My “serious” listening mode consists of moving my Magnepan .7’s away from the wall another foot. :crazy_face:

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Gotta give props to you Fats, amazing dedication to the hobby, very inspiring. Hope you have many hours of enjoyment for all the work you have done. Cheers, Jim

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Looking forward to having you come over and take a listen when Covid concerns simmer down.

This is another good article from the folks at ASC on how they helped treat a room with glass behind 30.7’s for a demonstration at an audio store. Good read. https://www.acousticsciences.com/media/news/acoustic-sciences-helping-magnepan-307-speakers

Shadow casting is another concept I learned from the folks at ASC. This concept is particularly relevant for the treble and mid panels on Maggies. I took this from an email from the Desk of Art Noxon. Good stuff.

Traditional Wall-Mounted Acoustics or Mobile Free-Standing?

For many, wall-mounted sound absorbers are the default style and the only thing that makes sense. Such a restricted mindset imposes limitations and adds cost to your room treatment. If one could achieve comparable sonic accuracy, with holographic imaging and immersive sound stage at one fifth the cost, would it be worth exploring? We say: yes.

This week we look at a simple, yet underutilized concept: Acoustic Shadow Casting.

Traditional Wall-Mounted Acoustics

In this example, a 5-unit wide sound absorbing panel casts an expanding shadow zone off the wall into the room.

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Free-Standing Acoustics

In this example, a non-traditional near-field sound absorbing panel is only one unit wide and still casts the same acoustic shadow into the room.

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Far-field Panel: Room Acoustics

The wall-mounted panel delivers 5 units of absorption to the room.
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The free-standing absorber delivers 1 unit of absorption to the room.

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…and the Overall Room Effect?

Both versions of absorber remove the same % of direct sound reaching the shadow zone, thus allowing the same degree of articulation and tonal accuracy. But, since the near-field panel is smaller than the far-field, it absorbs less energy and maintains a longer reverberation time.

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The result is a more reverberant room in the case of free-standing acoustics. Tame the reflections you intend to without over-deadening your room!

Which one is right for you?

As with so many things in life: it depends. Heavily furnished rooms can easily become “lifeless” in the treble range with excessive use of sound absorbers as all the natural “sparkle” is lost. Bare rooms with hard walls can benefit from carefully placed absorbers to reduce energy storage and scatter sound through diffraction. And it depends on your personal sonic preference.

Now you know, and knowing is half the battle.

Stay safe and happy listening to all!

~ASC TubeTrap

I forgot to include a great video of Art Noxon at the 2019 California audio show that taught me a lot about planar speakers and dynamic speakers and bass treatments. Around minutes 8 to 13 he talks about dynamic speaker wave forms vs dipole wave forms. He is a fan of dipole wave forms because he believes they are easier to treat and interact with rooms better than dynamics. Also around 55 minutes he talks about dynamic issues and then at 1 hour he talks about the advantages of the wave form from dipoles speakers. Note also that the video has a repeated section from 1hr 9 minutes to 1hr 24 minutes. When you hit 1hr 9 mn skip to 1hr 24. There is some good stuff at around 1hr 25min with respect to those of us that use subs with our Maggies. Similarly 1hr 34 to the end talks about harmonics and the rule of 1/3s. Watch and learn from a good resource.

https://www.acousticsciences.com/cas-2019-artstalk

Another email from Art Noxon about Polyfusers and their effects on the wave form. I like the flexibility of the GIK Polyfuser for a variety of applications. This email explains why a polyfuser may work well for dipoles

More Ripple Tank Fun: 2 Dipoles Playing Toward Polys.

Read to the end to see what happens!

Learn what makes a Poly Tick

Last week we showed you how to improve the spaciousness in your listening room. This week, we start things a day early and go into greater detail about the intricacies of a true polycylindrical diffuser. And, of course, show off some more cool ripple tank creations.

You have played with it, right?

“Poly” Want a Cracker?

Polys are formed by a shallow sections of a cylinder. This has ideal curvature all the way across with no hard corners.

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A half section of a cylinder is not a poly. It has undesirable reflection patterns when mounted against a hard surface (wall)*.

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A half cylinder has two parts: a curved poly part (good) and a corner part (bad). Corner reflections don’t scatter, they reflect right back where they came from.

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A corner reflection is useful if you are a surveyor but not in the world of sound diffusion.

*TubeTrap diffusers are hemi-cylindrical polys mounted atop broadband absorbers, therefore they do not create these hard corners. This is also why diffusers are smaller on HalfRound and QuarterRound TubeTraps.

Part 2: Now the Wavefront Has Expanded All the Way to the Polys. The Diffusion Has Begun!

DIY Diffuser (so easy!)

This is so easy to build, it’s hard not to build it. Try, we dare you!

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Get a thin flat panel that is a little wider than the backboard. ## DIY Diffuser (so fun!)

Bend the panel and snap it onto the backboard. See, you’re probably already done!

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But is This a Poly?

Not exactly. This is a catenary which is rounded in the middle third but flat on the other two side sections.

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The result is a sound spreading diffuse surface in the middle section and two beaming reflections off either side. No, not perfect, but at least the beaming sections are probably not parallel to your walls or speaker baffles (good).

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Part 3: A soft, smooth diffuse field returns to the front of the room, just like it would in an acoustically treated symphony hall.

Thank you very much for the information that you presented. I think that we may have corresponded before. I have the 1.7i’s coupled with the REL Carbon Limited subs. They blend seamlessly.
I have a question that you might answer. How would it work to use something like the GIK Evolution Polyfusors in the back of the 1.7i’s say within a foot or two? That would in theory diffuse the mid and high frequencies before they had a chance to get to a wall. This would also mean that I only needed one behind each speaker. What do you think? Thanks.
Bob

I would confirm with the folks with GIK but I think you want a little space between the polyfusers and the speakers. They are helpful folks and have reasonably priced products.

Looking at Audio Researchs set up above I have no doubt the a stack of gridfusers from GIK would work that close to the speaker. You definitely don’t want to have absorption of mid and treble behind the speaker

Also go to a hardware store and try the 8" diameter concrete cardboard molds and save your receipt. You can try them out and return them. Great diffusion experiment with no dollar cost.

Just curious if you ever tried your Maggies with the treble ribbons on the inside? And if so, what were your thoughts on inside vs outside placement?

I have done the treble on the inside. The soundstage is a little less wide but more defined. The Real issue is the bass panels are closer to the side walls in this configuration and I get too much bass reinforcement. The bass and mid bass color the soundstage a little too much in my room. Also the inside treble requires me to put more diffusion on the windows. Rooms and Maggie’s all mate differently.

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My “serious” mode means:

  1. putting a lawn cushion in front of the tv.
  2. moving the couch further away from the speakers by about 2’

And thanks @minnesotafats!! I will be reading and re-reading and re-looking at the description and photos you posted throughout time, even though my speakers are in a wood box :slight_smile:

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How would the asc tube traps (16”) compare to the gik soffits (cubes) ?
Would there be a diff in performance ?

The GIK Soffit Traps will be cheaper. The ASC TubeTrap does double duty as a polycylindrical diffuser as well as being a bass trap. If you can afford the investment in the TubeTraps, they are the more versatile room treatment @echoz.