Advice on Magnepan LCR placement behind AT screen? - AVS Forum
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post #1 of 18 Old 01-12-2008, 08:44 PM - Thread Starter
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I am going CIH with an AT Screen. Size 120" by 52".
My speakers are Magnepan. I have two 1.6 Qrs for Left and Right and a CC3 for center.
The 1.6s are about 6 feet tall and 20" wide and 2" thick, dipolar.
Should I place them so that the top of the speakers are even with the top of the screen?
I assume that the center CC3 should be placed directly center of the screen?
Left and right speakers should be placed at the edges of a 16:9 image correct?
Here is what I am replacing with an overview of what I was hoping to do. Ignore the screen size listed and the center channel vertical shape in the drawing. I have sinced changed my plan on size and center channel speaker since this rendering was made.

Thanks
Sean
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post #2 of 18 Old 01-14-2008, 05:21 PM
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No one has responded, so I have some thoughts/guesses. I use direct radiators and find that placing the L/R drivers at about the 1.85:1 edge gives me the best imaging for all aspect ratio films. I think some experimentation is in order for our setup, both in the horizontal as well as the vertical. Just a guess on my part, but I would try (among other scenarios) a vertically centered on the screen approach - where the bottom and top of the speakers extend equal distances above/below the screen for the L/R. I would experiment with different vertical centering of the center channel. Many people recommend "1/3" up vertical placement, but I am not a fan of generalized "rules". It is really hard to say what might work best in your setup, and I would try as many different setups as possible. I would not be afraid to try radically different than "recommended" setups, what is the harm in trying things? I know this post is likely not of too much help, just some thoughts. I am a big believer in empirical testing to determine things, personal preference plays the largest role in all things HT in my opinion.
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post #3 of 18 Old 01-14-2008, 05:43 PM
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Maggies need lots (and, lots) of breathing room...both behind and in front...in order to get anything that nears good sound...I would seriously rethink placing them behind the screen (let alone, near the rear wall). The screen will serve as an obstruction to the sound wave length when placed before the speaker.

Just my opinion.
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post #4 of 18 Old 01-16-2008, 12:24 AM
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Sean,

We should stay in touch. I am planning on the exact same set up with the possible exception that I may curve my 10' wide 2.37 SMX screen. I have the material but have not yet made the frame. Also have the Panamorph UH380. I already have the maggies and they are something else. I don't think there should be any difference between a direct radiator and the maggies as far as the AT screen is concerned. There is plenty of measured data to support this for direct radiators. The only potential issue I can see is acoustic interference with the screen frame due to the maggies size. I am already using my 1.6s and CC3 with my current screen 80" wide 16:9 Vutec 1.3 on the wall. My room is 14' wide and the maggies are about 2' out from the rear and side walls. They sound great in that location. I have them running through a DEQX, EAD Processor and Parasound 5 channel amp at the moment. I also have a Velodyne DD18 subwoofer tying in the low end. Eventually, I will assemble 4 UcD 400 class D amplifiers that I have laying around and biamp the 1.6s. Because I will be putting the SMX screen out front, it will probably be necessary to move the maggies closer to the rear wall. I could also mount them just to the outside of the screen, placing them very close to the side walls. In either case, I was planning on experimenting with acoustic absorbent/diffuser materials. Let's share notes. I am currently messing around with my RS-1 and Radiance but have got them calibrated pretty well for the moment. Maybe time to concentrate on the SMX screen and audio. As usualsusects points out, don't be afraid to experiment.

Mike
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post #5 of 18 Old 01-16-2008, 08:15 AM
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Quote:
Originally Posted by mikela View Post

Sean,

We should stay in touch. I am planning on the exact same set up with the possible exception that I may curve my 10' wide 2.37 SMX screen. I have the material but have not yet made the frame. Also have the Panamorph UH380. I already have the maggies and they are something else. I don't think there should be any difference between a direct radiator and the maggies as far as the AT screen is concerned. There is plenty of measured data to support this for direct radiators. The only potential issue I can see is acoustic interference with the screen frame due to the maggies size. I am already using my 1.6s and CC3 with my current screen 80" wide 16:9 Vutec 1.3 on the wall. My room is 14' wide and the maggies are about 2' out from the rear and side walls. They sound great in that location. I have them running through a DEQX, EAD Processor and Parasound 5 channel amp at the moment. I also have a Velodyne DD18 subwoofer tying in the low end. Eventually, I will assemble 4 UcD 400 class D amplifiers that I have laying around and biamp the 1.6s. Because I will be putting the SMX screen out front, it will probably be necessary to move the maggies closer to the rear wall. I could also mount them just to the outside of the screen, placing them very close to the side walls. In either case, I was planning on experimenting with acoustic absorbent/diffuser materials. Let's share notes. I am currently messing around with my RS-1 and Radiance but have got them calibrated pretty well for the moment. Maybe time to concentrate on the SMX screen and audio. As usualsusects points out, don't be afraid to experiment.

Mike

Sean,

What he said, and...

I would try to do the experiments as cheaply as possible.

I have been surprised by some of the changes that were made to my Newform Research R645's by placement (monopole ribbon tweeters), as well as furniture placement in the room. Putting my RPTV between them made a very noticeable difference.

I need to put my SMX up in front of my Newforms to see what they will sound like. Will I lose the soundstage and the ability to go without a center channel like I am running them now? Only checking that out will tell for sure.

If maggies were just like other speakers, who would bother with them? ( intended in a good way ) The dipole thing really does make a difference, and a nominally AT screen might make a difference with them that it does not with other designs.

You never know until you try. And sound perception is one of those things that involves a heavy dose of personal preference, so you will never really know for yourself, in your room, until you try it for yourself, in your room.

I understand why you asked, though. I would like to hear the thoughts of anyone who has already tried it, just out of curiosity.

Best Regards,
Doug
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post #6 of 18 Old 01-16-2008, 01:28 PM - Thread Starter
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Thank you all for the very thoughtful replies!
I hope to begin the new screen wall fabrication within the next week. I'm currently waiting for the screen material which is about 7 days out.
I'm going to try the Pfifer Shearweave 4500 material.
I will definately keep you all posted once I get started and how the maggies handle their new placement.
I wanted to give them a chance to peform for me in this new set up before selling them for 40 cents on the dollar at this point
For what its worth, Chris at seymourAV assures me that the maggies will tolerate the screen material well and he is confident that if I can give the maggies the room they require, the sound from the screen should be quite enjoyable.
Thanks again for the replies.
Sean
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post #7 of 18 Old 01-16-2008, 06:30 PM
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You could also try to look at audioasylum?

Link for search of theater in the planar subforum at Audioasylum

Be forewarned, though, they aren't entirely TIC with their name. For some of them it really fits.

Best regards,
Doug
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post #8 of 18 Old 01-13-2014, 09:53 PM
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Interesting thread. Found it when searching for info about how Magnepan recently demoed their speakers at ces behind an acoustically transparent cloth.....

Curious to know what the OP decided to do.

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post #9 of 18 Old 01-13-2014, 10:03 PM
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Here is what I was searching for. Maggie's behind a curtain. Similar concept.

http://parttimeaudiophile.com/2013/02/05/las-vegas-2013-magnepans-big-bass-boogie/

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post #10 of 18 Old 01-13-2014, 10:24 PM
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And they did something similar he prior year. Looks like the key is to have a deeper 'behind the curtains' depth than people would usually plan for.

http://www.stereophile.com/content/magepan-show

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post #11 of 18 Old 01-13-2014, 10:29 PM
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And another year at ces, actually theshow.

http://www.theaudiobeat.com/ces2014/ces2014_magnepan.htm

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post #12 of 18 Old 01-17-2014, 03:30 AM
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If this was my system, yes I would be placing the L and R just inside the 16:9 image width. As for centre, ideally you want the LCRs to be all at the same height. If your L and R speakers are floor standers, then I would be aiming to get the C as close to their height as possible.



In my case I have 3 identical LCR speakers, so no problems getting them at the same height. HERE is the link to my AT screen build.

Hope this helps.

Mark Techer

I love my Constant Image Height system!
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post #13 of 18 Old 01-25-2014, 02:53 PM
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With the maggies right up against back wall there will be no attenuation of the backwave (in air) so the reflected wave back into the planar diaphram will generate some pretty serious comb filtering at certain frequencies. That's not something you can fix with the DEQX because it's all in the time domain.....

 

I would grab a copy of matlab or some other (free) software to calculate where the comb filtering is going to be most extreme. This is a set of frequencies which will change based on the distance between the speaker panel and the back wall. This won't be exact because, obviously,  the panels will be angled from the wall, not parallel

 

Next I would look at a table of absorption coefficients for various types and thicknesses of owens corning or roxul to find the depth of material needed to damp the problem frequencies. With any luck 1-2" of O-C with the maggies an inch or two away will be ok.

 

You can also get approximately the same result experimentally, by downloading REW, setting up a measurement microphone and putting one panel  in the center of the long wall in the room. Play some pink noise (REW generates it for you) and do sweeps, moving the panel out from the wall in 1/2" increments. Save all the raw frequency plots. Don't use any smoothing.

 

Take a sweep with the panel in the middle of the room to get the "reference frequency response" of the 1.6 panel. Eye balling all the plots should tell you approximately what frequencies the damping has to address.

 

Dipolars have huge potential in home thearters. Too bad they'e so, um, damn big. I've never heard point source speakers that can match the size of the sound stage, or convey the live ambient sound mixes in some of the best blu-rays. I find that I can turn the volume way down as compared to dynamic speakers; which has saved me the cost of some renovation for sound control. I would get a 1.6 for the center speaker as well. The dialog clarity is just so much better.

 

I have Martin-Logans with the conventional cone bass drivers so they can't sit that close to the back wall. In my case i had to build some QRD diffusers to accomplish the same goal. Hopefully you won't have to go to that extreme.

 

Here's where I started using the mathematical approach (for absorbers or diffusers): 

 

https://play.google.com/store/books/details?id=485No8PAv2UC&rdid=book-485No8PAv2UC&rdot=1&source=gbs_vpt_read&pcampaignid=books_booksearch_viewport

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post #14 of 18 Old 01-26-2014, 12:24 AM
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With the maggies right up against back wall there will be no attenuation of the backwave (in air) so the reflected wave back into the planar diaphram will generate some pretty serious comb filtering at certain frequencies. That's not something you can fix with the DEQX because it's all in the time domain.....

I would grab a copy of matlab or some other (free) software to calculate where the comb filtering is going to be most extreme. This is a set of frequencies which will change based on the distance between the speaker panel and the back wall. This won't be exact because, obviously,  the panels will be angled from the wall, not parallel

Next I would look at a table of absorption coefficients for various types and thicknesses of owens corning or roxul to find the depth of material needed to damp the problem frequencies. With any luck 1-2" of O-C with the maggies an inch or two away will be ok.

You can also get approximately the same result experimentally, by downloading REW, setting up a measurement microphone and putting one panel  in the center of the long wall in the room. Play some pink noise (REW generates it for you) and do sweeps, moving the panel out from the wall in 1/2" increments. Save all the raw frequency plots. Don't use any smoothing.

Take a sweep with the panel in the middle of the room to get the "reference frequency response" of the 1.6 panel. Eye balling all the plots should tell you approximately what frequencies the damping has to address.

Dipolars have huge potential in home thearters. Too bad they'e so, um, damn big. I've never heard point source speakers that can match the size of the sound stage, or convey the live ambient sound mixes in some of the best blu-rays. I find that I can turn the volume way down as compared to dynamic speakers; which has saved me the cost of some renovation for sound control. I would get a 1.6 for the center speaker as well. The dialog clarity is just so much better.

I have Martin-Logans with the conventional cone bass drivers so they can't sit that close to the back wall. In my case i had to build some QRD diffusers to accomplish the same goal. Hopefully you won't have to go to that extreme.

Here's where I started using the mathematical approach (for absorbers or diffusers): 

https://play.google.com/store/books/details?id=485No8PAv2UC&rdid=book-485No8PAv2UC&rdot=1&source=gbs_vpt_read&pcampaignid=books_booksearch_viewport

That's very interesting.

Do you have a photo of your setup?

How far away from the front wall, in front of the diffusers, do you have your speakers?

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post #15 of 18 Old 01-26-2014, 03:47 PM
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Quote:
Originally Posted by nathan_h View Post


That's very interesting.

Do you have a photo of your setup?

How far away from the front wall, in front of the diffusers, do you have your speakers?

 

No, sorry. The interesting bits are in the hall way at this moment, waiting for the carpet company to replace the builders-beige Berber with something that can only be described as "outraged spouse grey"; plus hanging the Elite Lunette 2.35:1 screen (replacing a well loved Hi-Power model B) that is ridiculously oversized for the room.

 

I'll post some pix when the work is done.

 

My HT is basically a dogs breakfast. It's a spare bedroom that serves as my home office 5 days a week, into which I shoe-horned a bunch of AV equipment. It breaks every principal for good acoustic design, hence the need for aggressive treatment.

 

The QRD diffusers are from http://www.decware.com. I did all the work on matlab to figure out the comb filtering worst case scenarios, then went to various sites for DIY 13th order QRD construction, but didn't have the extra time to build them. It's incredibly labor intensive, as others on this forum have described. The decware units are 13th order and reasonably priced.

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post #16 of 18 Old 05-23-2014, 02:03 PM
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...with the maggies...would a screen that allows sound to come through (with a Lunette curved screen) be something to consider even though the maggies themselves (left/right) would be on the side of the screen?...would this allow the maggies to have larger breathing room for sound? (hope this makes sense)...
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post #17 of 18 Old 05-24-2014, 04:36 PM
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Unlikely to hurt IMO.

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post #18 of 18 Old 05-24-2014, 06:04 PM
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Unlikely to hurt IMO.

...thanks, nathan_h
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