Speaker-Screen Positioning

Posted by: donlboy

Speaker-Screen Positioning - 01/25/10 11:15 PM

I'm looking at using an AT screen with speakers behind and can't make sense of the geometry based on the guidelines I see. The SMPTE guidelines are for a viewing distance of 1.86 times screen width, which gives a viewing angle of about 30 degrees, and the THX guidelines are for a 26-36 degree viewing angle, so they are pretty similar. But recommended speaker listening angles are around 45-60 degrees for home theater (maybe less for 2-channel). In practical terms, for a 120" diagonal screen the viewing distance would be around 16 feet, and the listening distance would be around 8 feet (to keep the speakers within the 105" width of the screen). I understand some compromise from the ideal is OK, but this seems too far off to compromise. For a normal screen the L and R speakers would be outside the screen edges, so the optimum ratios can be met for both video and audio. What am I missing about using an AT screen?
Posted by: PhillipD

Re: Speaker-Screen Positioning - 01/26/10 12:41 AM

I would try moving the L/R just inside the screen as long as there is no border interferance and have the center channel in the direct center. I think the most important thing is to have all the L/C/R channel tweeters at prime seating lear level. For me I have two rows so I went with row one as the prime row, if you have three rows I would slpit the differeance and have them set for the second row height.

if you can try this out for a few movies and then if you like for S&G you can move them out side to the higher angles and see if you are missing anything. I will bet you find you are not missing too much but I have been known to lose the odd bet LOL

You can also try these links:
http://www.avsforum.com/avs-vb/showthread.php?t=974274
http://www.avforums.com/forums/projector...ice-needed.html


later
Phil
Posted by: grunt

Re: Speaker-Screen Positioning - 01/26/10 02:42 AM

Iím curious what reason you have for wanting an AT screen. Not that they donít have there uses but just because itís AT doesnít mean your overall setup will be better as it really depends on the situation IMO.

You really should determine what screen width you want by experimenting and not just following someone elseís guidelines. If you donít already have a projector you can shine on the wall to gauge screen size from then the best way I know is to go to a theater and find the seat that gives you the best viewing angle. Pace off the width of the screen and the distance to it from that row and calculate your own screen width to seating distance ratio.

That said thereís only a few ways to reconcile the angles.

Use as wide a screen as you are comfortable with and put the L/R mains as far out as you can and live with it. By my calculation your seating would only be 13í away from a 105í wide screen at a 36 degree angle. You may also find you actually prefer to sit closer.

Put only the center speaker behind the AT screen allowing the L/R mains to be positioned farther out. This may also allow some more flexibility in placing the mains to give you the best overall soundstage rather than your screen dictating how your soundstage is set up.

The best way I could figure out was to ditch the idea I had to use an AT screen and go with a standard screen with my speakers under it. Doing this I avoided the risk of morieí and any possible sonic hit to the high frequencies caused by the AT screen. It also gives me complete placement flexibility for my front 3 speakers so I can have the best possible soundstage.
Posted by: JohnK

Re: Speaker-Screen Positioning - 01/26/10 04:00 AM

Don, yes you're right that the suggested viewing and listening distances are quite a bit different. For your 120" screen example a 12' distance could be used as a compromise that should work acceptably for both visual and audible factors.

As Dean questioned, however, why is the AT screen concept so attractive? Mains positioned outside a regular screen and an identical or at least similar(e.g., M22 with M80s)vertical center below it would work well. Or, if the AT screen is used, consider placing only the center actually behind it, with the mains wider and outside.
Posted by: SirQuack

Re: Speaker-Screen Positioning - 01/26/10 07:56 AM

I agree as well, not sure why people are so interested in AT screens. I want to "see" my investment, why hide what you paid for? Also, getting the speakers setup for best soundstage requires trial and error, you will be limited if you hide them behind a screen.
Posted by: donlboy

Re: Speaker-Screen Positioning - 01/26/10 08:59 AM

I have been looking at an AT screen mainly to get the speakers in optimal relation to the screen. Also, this will be a mostly HT/music room, but will also double as a family/rec room with grandsons, so have been thinking about speaker vulnerability. I don't have room for a 120" screen (16:9) with L & R speakers flanking it, so may have to drop down to smaller screen with speakers to the side. That would simplify some wall construction issues I would have with the AT setup.
Posted by: alan

Re: Speaker-Screen Positioning - 01/26/10 11:08 AM

Hi Donlboy,

I would echo the comments already made here. Most AT screens cause various reflections and audio anomalies as well as visual degradation. If you still want to go with an AT screen, here's a link to some interesting tests done by Mix magazine. Only one of those tested was reasonably transparent in terms of audible degradation of frequency response:

http://mixguides.com/studiodesign/product_features/new-perforated-screens-0405/

The dispersion of good speakers like Axiom really make the notion of optimal speaker placement in relation to the screen a non-issue.

Regards,
Alan
Posted by: Potatohead

Re: Speaker-Screen Positioning - 01/26/10 02:21 PM

I had the same "problem" about 5 or 6 months ago. Do you use a larger A/T screen and put the speakers behind it, or do you use a normal, smaller screen and place the speakers beside/below it? i was limited to 12' width and had to choose one or the other. I chose the latter personally, I went with a 110" diagonal when I was hoping for more like 120". I sit about 15' back from it. I just have a hard time believing the screen doesn't affect sound quality, and we do know the screen affects picture brightness. I just was not willing to sacrifice both audio and video quality to gain less than 10% in screen size.

Of course your opinion may differ and I know many people are happy with A/T screens. I do recall reading a test someone posted here once though where they tested three screens, and the only one that was decent was about three times the price of the others.
Posted by: SirQuack

Re: Speaker-Screen Positioning - 01/26/10 03:23 PM

My room is also a HT/Rec Room that is 8,000 cu ft. The kids stay away from the speakers if you teach them. \:\) My boys always have movie nights and it works out fine.
Posted by: donlboy

Re: Speaker-Screen Positioning - 01/26/10 06:34 PM

Alan-

Thanks for your input. I have been considering the AT screen material from Seymour AV - they're in my neck of the woods in Ames Iowa (I'm in Ankeny). They seem to have designed their latest fabric to minimize most of the issues raised in the Mix article you referenced. I would appreciate your comments on the information in this link: Seymour AV Screen Design and Tests. I haven't yet seen the screens in action, but plan to in the near future before I decide which way to go. I can make a 103.3" diagonal DIY screen for about $350, so it is attractive, but of course it has to perform.
Posted by: Murph

Re: Speaker-Screen Positioning - 01/27/10 08:12 AM

If you do some searching, you will find a lot of success stories from people who went the DIY route using a big sheet of laminate from Wilsonart. In fact, somebody even posted spectograph (or something) tests suggesting that performance was equal to or sometimes better than many commercial screens costing thousands of dollars.

I am extremely please with the results from my $200 sheet of Wilsonart Designer white. I think a Wilsonart grey color is also recommended as well depending on the brightness of your room.
Posted by: roar

Re: Speaker-Screen Positioning - 01/27/10 09:41 AM

I have a DIY AT screen and I am very happy with it. For those of you who would argue that an AT screen limits your ability to produce the 'best' sound stage I would argue the exact opposite... depending on your definition of what the best sound stage is of course.

If the point of your home theatre is to emulate a 'real' theatre experience, then I believe the best sound stage is one that comes as close to replicating that setup as possible and that would be one where your speakers are behind the screen. If your definition of the best sound stage is the one that sounds the best, well then, I think it is clear that an AT screen isn't for you. I also think a home theatre is often made up of compromises and one way isn't more right than another.

I'll be completely honest and say I've never been behind the screen at a my local theatres but I have been to IMAX presentations where they turn the lights on behind the screen and show you the speakers that are there, so I am of the belief that the majority of the theatres I go to have speakers back there. With that thought in mind, it is my opinion that the best soundstage is one that can have the speakers behind the screen, where the voice calls come from the center of screen, not above it, not below it. Further to that your left and right channel sound is actually coming from the picture, not from beside the picture.

I went the AT for other reasons as well. One of which it allows you to use the complete width of your room, if you need to factor in the widths of your speakers when looking at screen size you are losing at least a good foot to a foot and half of width which could be used for a bigger screen!

For me, personally, I prefer the look of a theatre with an AT screen, I like not seeing where the sound is coming from, I think it helps immerse you into the picture more when your screen goes wall to wall and there is nothing but a screen in front of you. I'm really not concerned about what I paid for my speakers and don't need to be reminded of that investment so hiding them behind a screen is alright with me. \:\)

As far as degradation of picture quality and sound quality goes, I'm sure there is some, but on my $1,500 720p projector, does it really matter? Maybe if I was using a $8k JVC or >$10k Sim or Runco, sure, then I may have a different opinion, but for me, my picture looks fantastic. In regards to sound, again, I would bet a fair penny that every person who has ever stepped foot in my theatre would not be able to hear a difference if those speakers where in front of the screen or behind the screen. I certainly don't doubt there are people out there who could tell, I just don't know any of them, besides my room has a lot bigger acoustical problems than a couple of pieces of AT material in front of the speakers!

Blind tests are often encouraged around here for people to really test what they think they are hearing is actually what they are hearing, has anyone reading this thread ever had a chance to do a blind listening test with AT material, themselves, personally? I'd be curious to know if they heard a difference, I know microphones can pick up differences, but can you?

Sorry for the long reply \:\)