Diffusers behind planar speakers - AVS Forum
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post #1 of 14 Old 03-18-2011, 12:48 PM - Thread Starter
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I saw a picture in the sticky thread where a guy has these giant planars with diffusers on the wall behind. Since the speakers are dipolar, isn't a significant amount of the sound supposed to reflect off of the back wall? This doesn't adversely affect the sound from them?
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post #2 of 14 Old 03-18-2011, 01:29 PM
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I use Magnepan planars, large ones I don't know if a shot I posted is one you are referring to but I'll give you my 2 cents based on personal experience.

I have diffusers behind behind them specifically to deal with reflections off a large window between them. There is no right or wrong answer here, because each room has its own unique acoustic issues. Mine was harsh & beaming upper mids in the hi female vocal range. The diffusers tamed that.

And you are correct that the idea of dipolar/bipolar speakers is to have reflected sound off the wall to open up the soundstage, more sense of depth, etc.

I've owned magnepans since '82 and in house 1 I had no such problems due to using them on a long wall with small windows that had woven woods. House 2 I have larger ones on the short wall, and close to side walls with the rear wave going into the 2 corners + large window bay. According to some acoustic folks, this made comb filtering of certain freq's worse with the result being the beaming effect. The diffusers are placed right in the window bay. And they helped without ruining the trademark sound of the speaker.

Some like to treat the front wall with diffusers or absorption, many don't. It all depends on the room.

You are observant to ask

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post #3 of 14 Old 03-18-2011, 01:36 PM - Thread Starter
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No, it was a guy named Vinyl: http://www.avsforum.com/avs-vb/showt...1217536&page=3

I don't see a post by you in the thread. The reason why I asked is 'cause I have a pair of Magneplanar SMGb's. And yes, I love them.
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post #4 of 14 Old 03-18-2011, 03:33 PM
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Nope - you're right it wasn't me in that thread
I recently posted some pics in the pioneer SC-09TX thread.

Glad you're enjoying your Maggies Do you use yours just for music or a full HT setup?

I saw that pic myself not too long ago. Again, each situation is different, but (there's always a but ) his might be a bit overboard. With bare walls, I probably would have left it alone or just used several diffusers, but not use so much absorption behind them. Bass traps along side are OK. For all intents, he's reflected or deliberately killing a lot of the rear wave. But he has a hard floor, so it may have helped him. If you have large enough space, no nearby side walls & have carpeted floor, I can't see the need for that much treatment. I never did until forced to by my situation. I'm also experimenting with 2 - 6" thick bass traps behind mine, and truthfully, I think they sound worse with them. So you can have too much.

I also found a pic showing what I think is considered use of treatments near tight corners. Mine is the 2nd one with the plasma to give you another perspective.
LL
LL

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post #5 of 14 Old 03-18-2011, 03:58 PM - Thread Starter
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From that pic, your room looks way too small for those speakers, but that's probably just the perspective. My room is definitely too small for mine. To answer your question, both. After much self grumbling and thought, I went with a 3.1 setup as a compromise. The center channel is, obviously, completely unused for music (but it sounds like the vocals are coming right from it, amazing imaging by the maggies). I got a couple of additions to make that'll be done this weekend, maybe even tonight. When I'm done, I'll post up my system.
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post #6 of 14 Old 03-18-2011, 06:52 PM
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Quote:
Originally Posted by ss9001 View Post

And you are correct that the idea of dipolar/bipolar speakers is to have reflected sound off the wall to open up the soundstage, more sense of depth, etc.

Roger that, but one is trading envelopment for some temporal smearing and less-precise imaging. As you say, there's no "right" answer and my fellow Martin Logan owners follow different paths to different goals, much as Maggie owners probably do. Best advice for the OP is to experiment with front wall absorption/diffusion and decide what works best for him.

After much experimenting and general screwing around, I ended up with absorption on pretty much the entire front wall.
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post #7 of 14 Old 03-18-2011, 08:47 PM
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Havingowned both planar and electrostats I can say from my experience diffusers work great with no negative affects. It doesnt have any negative affect on image or focus and stage...it simply breaks up backwave to avoid beaming, smearing and fatigue so I think everyone should atleast try some solution be it plants..booksheves or an actual audio product.
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post #8 of 14 Old 03-20-2011, 06:12 PM
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Have you considered building your own diffuser - it's not that difficult. Try visiting this website to learn how to build your own Skyline diffuser for your front wall behind each speaker. This is the best and most accurate Skyline calculator I can find that follows the RPG's US Patent:

http://www.oliverprime.com/prd.php

I've written a doc on how to use it should you be interested. I've used the link to build several of them.

 

DIY Skyline Diffuser 1.pdf 212.478515625k . file
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post #9 of 14 Old 03-20-2011, 07:05 PM - Thread Starter
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My room isn't particularly boxy and has lots of angles and stuff. I don't think a diffuser would help me very much.
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post #10 of 14 Old 03-21-2011, 12:23 PM
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Quote:
Originally Posted by pistonengine View Post

My room isn't particularly boxy and has lots of angles and stuff. I don't think a diffuser would help me very much.

There is no room that has so many angles that a 4x2 backwave of sound cant beam around so dont kid yourself, you want to break up that wave behind speaker BEFORE it heads out in the room, no matter what shape the room is.
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post #11 of 14 Old 03-21-2011, 01:09 PM - Thread Starter
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Sorry, didn't mean to dismiss the idea like that. What I meant was that the room isn't awful and diffusers aren't a big priority for me. But I appreciate the suggestion.
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post #12 of 14 Old 03-21-2011, 01:49 PM
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Quote:
Originally Posted by kevinzoe View Post

Have you considered building your own diffuser - it's not that difficult. Try visiting this website to learn how to build your own Skyline diffuser for your front wall behind each speaker. This is the best and most accurate Skyline calculator I can find that follows the RPG's US Patent:

http://www.oliverprime.com/prd.php

I've written a doc on how to use it should you be interested. I've used the link to build several of them.

be careful with large gaps like that -- your diffuser may be absorbing more than you think (which defeats the purpose).

i have a 2D PRD but im going to go back to 1D QRDs... the 2D just disperses too much energy (since it's doing it in both planes) and it's really unnecessary for me. a late arriving diffused soundfield via the side walls is what im after. but all depends on your design requirements.
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post #13 of 14 Old 03-21-2011, 05:35 PM
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Quote:
Originally Posted by localhost127 View Post

be careful with large gaps like that -- your diffuser may be absorbing more than you think (which defeats the purpose).

i have a 2D PRD but im going to go back to 1D QRDs... the 2D just disperses too much energy (since it's doing it in both planes) and it's really unnecessary for me. a late arriving diffused soundfield via the side walls is what im after. but all depends on your design requirements.

Local host - Ok, I'll bite . . . large gaps like what?! If you're commenting on the cell size of my Skyline per the attached .pdf photo which has cell sizes of only 1.5"*1.5" then that hardly constitutes 'large gaps.' Afterall, Massenburg's Studio C is only 1"*1" cell sizes. Has the close up photo mis-led you? Or are you commenting on the sliver sized 'gaps' between the wooden blocks that only the very highest of frequencies would 'see?' Sorry but you're sounding a tad anal and condescending. The wall size covered by said diffuser is but a tiny fraction of total surface space and significantly more absorption will be done via furniture, carpeting, people, air itself etc etc.

Maybe I'm not understanding you but a 2D diffuser doesn't "disperse too much energy" - it diffuses and scatters just as much energy as a 1D diffuser but 50% of it travels in the vertical domain and 50% in the horizontal domain. For side walls you're better off with lateral diffusion that is accomplished by either hemi-cylindrical or QRD diffusers to help widen the apparent source width (ASW). The benefit of the hemi is that it doesn't offer temporal affects so you can sit closer to it should you have a narrow room, othewise you'll have to sit 3X the lowest design frequency of the QRD to accommodate the temporal affects.

Would you like to show us pics of your DIY diffusers?
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post #14 of 14 Old 03-21-2011, 06:16 PM
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Quote:
Originally Posted by kevinzoe View Post

Local host - Ok, I'll bite . . . large gaps like what?! If you're commenting on the cell size of my Skyline per the attached .pdf photo which has cell sizes of only 1.5"*1.5" then that hardly constitutes 'large gaps.' Afterall, Massenburg's Studio C is only 1"*1" cell sizes. Has the close up photo mis-led you? Or are you commenting on the sliver sized 'gaps' between the wooden blocks that only the very highest of frequencies would 'see?'

i was referring to the gaps at the base (between the blocks) ... and you are correct, they are only seen by freqs well above the audible range; but i thought i read in d'antonio's book (and confirmed over at GS forums) that having the blocks not sealed properly like that will in turn start to function like a very complex absorber - not something you would want in a diffuser (obviously) - and for 1Ds you especially want the wells to be sealed properly.


Quote:
Originally Posted by kevinzoe View Post

Sorry but you're sounding a tad anal and condescending. The wall size covered by said diffuser is but a tiny fraction of total surface space and significantly more absorption will be done via furniture, carpeting, people, air itself etc etc.

it's not being anal. im just forwarding along the same information that was provided to me. please dont take everything so seriously...it was complimentary information to your post.


Quote:
Originally Posted by kevinzoe View Post

Maybe I'm not understanding you but a 2D diffuser doesn't "disperse too much energy" - it diffuses and scatters just as much energy as a 1D diffuser but 50% of it travels in the vertical domain and 50% in the horizontal domain. For side walls you're better off with lateral diffusion that is accomplished by either hemi-cylindrical or QRD diffusers to help widen the apparent source width (ASW). The benefit of the hemi is that it doesn't offer temporal affects so you can sit closer to it should you have a narrow room, othewise you'll have to sit 3X the lowest design frequency of the QRD to accommodate the temporal affects.

correct - poor choice of words on my part.
what i meant is, it should depend on the design requirements whether to build 1D or 2D .. and it might be possible to assume that for the majority of people, 1Ds might work better unless you specifically need to disperse in both planes. again, depends on the design requirements.
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