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Taming/Damping Electrostat Backwave

In my understanding of the physics of the situation, the signal coming off the back of an electrostat panel is the same signal that comes off the front though in opposite phase. If there are reflections off a back wall, they cannot be a better signal than the one off the front of the panel. It strikes me that in a strict sense, if one could COMPLETELY eliminate the backwave on electrostatic speakers (a giant silent sound vacuum, sucking in the sound off the back of the dipole), this would be, in the words of the once famous and now infamous [:)] Martha Stewart, 'a good thing'. Am I missing something? Is there any argument to support not trying to eliminate the backwave through all means possible?

My Martin Logan SL3s sound reasonably intolerable when too close to the back wall, great when a certain distance away, and in my limited, ad hoc, distinctly non-scientific (not to mention bad WAF) experiments, even better when I put a variety of dampening material between the panel and the back wall (even when the wall is 6ft back).

Does anyone have a view or experience on the "complete backwave elimination" strategy? Do you try to eliminate it entirely? Do you leave some backwave in for 'flavor'? How do you deal with it? Put shag carpeting on the wall? Hire tall sheepdogs to sit on stools calmly for hours on end a la Fay Ray? I would love to know how other people deal with the backwave issue...
t_bone
dennis_the_menace's avatar
dennis_the_menace
467 posts
 
I experimented this weekend with speaker placement, using my Logan Aerius i. I took the speakers and placed them so that they had about 7 feet from the back wall, and also place some different "objects" (furniture, books, a lamp, etc) behind the speakers to break up the backwave.

I was surprised to find that the sound became thinner. The music didn't have the same rich depth or fullness that I acheived with the panels simply 3 feet from a plaster wall.

This made me think that, as Zaikesman says, Martin Logan designed these speakers with careful consideration to the backwave.

I don't know if all logans have them, but the Aerius have pieces of transparent thick plastic stuck to the backside of the panels. These may act as sufficient breaks in the backwave.
tom_nice
387 posts
 
My experience with Quad ESL 63's might be slighly helpful, in that it tends to confirm your main intuition about total absorption of the backwave. At first I built DIY Styrofoam diffusors imitating the RPG Omniffusor, and placed them on stands parallel to the back wall and about 2.5' on average behind the toed-in Quads. That was a big improvement over having nothing behind the Quads. Then I became persuaded that absorption, not diffusion, was the way to go with this backwave, and I filled in the diffusor wells with polyester fiberfil (from a fabric store), and that improved the sound quite a bit. I haven't gone further than that because as far as my ears can tell, I don't have to. I also don't know quite how I'd proceed if I wanted still more absorption, without messing up the looks of the room, making it hard to get at windows, and so on--annoying practical difficulties.

When I believed in diffusion, I once advised a Martin Logan owner to try Argent Room Lenses behind his. I tried them behind my Quads, for which they're a wrong shape, and they didn't work at all well. That figures, given the wrong shape and the fact that absorption, not diffusion, is wanted. Further, the Room Lenses don't absorb at all, while my DIY Styrofoam diffusors--design info supplied on request, and on Room Lens clones too, by t he way--definitely do.
newbee
4,767 posts
 
tom, my experience with 63's was some what parallel to your's but with different results. I tried deadening the back wave, partially and totally with poor results. I ended up with the speakers about 4 1/2 feet from the back wall toed in about 15 degrees with the back wave firing into irregular materiels, i.e. books, plants with round plant stands, etc including the corner of the room. the speakers were firing down the length of the room to a listening position 4 1/2 feet from the back wall. Gsreat result w/ flat bass/midrange frequency response.

Dennis, when you pulled your speakers out 7 feet from the wall you may have successfully eliminated any bass reinforcement from the nearby walls - this would emphasize the upper frequencies and make them sound thin. most manufacturers assume that there will be wall reinforcement, especially in smaller systems w/cone speakers(as i recall your speakers have a dynamic woofer?).
antinn
395 posts
 
I have owned ML's for over 10 years, and currently own ML Ascents. My current room treatment is a combination of four 2'x4'x1" acoustic panels and two ASC Tube Traps. The speakers are 50" from the rear wall, 26" from the side wall and toed-in about 15 degrees. The corner tube traps have the diffuser facing the speakers, with one acoustic panel mounted behind each speaker, but 24" from the side wall so they do not completely absorb the back wave. I then mounted one acoustic panel to absorb the reflection from the back wall. Since the panels are curved and slightly toed-in, side wall reflections from the back wall and the tube trap diffuser will confuse and brighten the image. The results are a very stable image, beautiful detail, but very relaxed with the speakers all but disappearing. Hope this helps.
hififuchs's avatar
hififuchs
16 posts
 

Hi,

I am fully aware that this statement, copied from above, is very old :"Room Lenses work wonders behind 'stats." Despite that I wonder if any of you could share some more specific experience using/positioning room lenses behind/beside electrostatic speakers?

My Speakers are Martin Logan Aerius (not i). Since app. one year I have two DIY Room Lenses standing behind my speakers. My room does not allow placing one room lens in the middle between the speakers.

What are your experiences when it comes to distance behind the panels?

Do you angle (toe in or out) the room lenses?

I read somewhere that some people cover the lenses with foam/cloth to absorb some of the back waves. Any thoughts on that?

Any experience from you are highly appreciated. 

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