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Discussion Starter #1
I have two separate questions...

(1) I want to get opinions and feedback from people with personal experience in the following matter. I have the Onkyo TX-SR805 with a 7.1 (THX) speaker setup. The Ultra2 Cinema/Music/Game modes take advantage of the ASA speaker configuration, right? I am (barely) beginning to watch movies and play PS3 games in uncompressed 7.1ch formats (no bitstream output of DTHD/DTSMA for PS3 quite yet) through HDMI. My dilema is which speaker configuration to use.. I know as you spread the SBR & SBL apart (& set THX SB spacing in menu accordingly) the ASA effect is reduced. Even THX says the speakers should be touching. I DO watch a lot of 5.1 movies, as most of you probably do as well, so the Ultra2 Cinema mode is especially important to me to get the full effect. What happens if I use this configuration for true 7.1 pcm audio? I am assuming since the 805 only allows the "THX Cinema" mode while playing back 7.1 pcm, that the ASA is NOT active and therefore the SBL and SBR speakers will have little or no audio separation.. What do YOU recommend/what are your experiences with this dilema??


Question (2): Without regard to the first question, the owners manual for the 805 provides what I'd consider a very minimum of information regarding setup (especially THX setup) of listening modes and speaker configurations. I have read on Home Theatre HIFI (can't find page at the moment) that Ultra2 Cinema IS in fact able to recognize the surround EX flag and play it back properly. My receiver by default is set to "auto" in the menus which switches it into the THX Surround EX mode, cancelling Ultra2 Cinema mode. When playing EX material with the SB speakers touching (as in ASA setup) IN the THX-EX mode, the SB speakers become more localizable and if your're sitting off center, it seems to draw your attention to the location of the speakers. IF IN FACT Ultra2 Cinema can decode EX material, then I would ASSUME it would spread the SB information out a little toward the side surrounds much like it spreads the side surrounds toward the SB speakers when listening to 5.1 NON-EX material. In this case, the reciever menus allow you to switch the "Auto" mode to "Manual" allowing you to pick pretty much any playback mode. I just don't want to do something stupid and shoot myself in the foot. By that I mean, maybe the info I read about Ultra2 Cinema being able to recognize and decode EX was wrong and I'd be losing some playback audio.. ANY insight you can provide would be MUCH appreciated. Thanks for your time!!! Levi
 

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Quote:
Originally Posted by lallen3 /forum/post/12942798


THX says the speakers should be touching. ...What happens if I use this configuration for true 7.1 pcm audio?

You lose any left-vs-right separation in the surround-back channels. Using Spatializer-like processing (such as ASA) won't recover stereo imaging behind you they way physically separating the rear speakers would.
Quote:
What do YOU recommend/what are your experiences with this dilema??

Consider an alternate placement scheme for the rear speakers. See attached.


Sanjay
 

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Discussion Starter #3
Thanks for the reply. I am well aware of Dolby's speaker layout, but the trouble is, the distance from the seating location to the rear wall is only about 4.5 feet. So when the speakers are 60 degrees apart (happens to be also about 4 feet) then there is a sound "gap" in the middle area.... That's why I'm trying to reconfigure it to spread the sound. This setup will only be use for another 8 months, then I'll switch to a "regular" 7.1 layout..
 

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If the back wall is 4.5 feet behind you, then a 60 degree spread for the rear speakers will be about 5.4 feet apart. Toe-ing in the rear speakers (pointing them towards you) should eliminate any sonic gap you're hearing between them.


Sanjay
 

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Quote:
Originally Posted by sdurani /forum/post/12947404


If the back wall is 4.5 feet behind you, then a 60 degree spread for the rear speakers will be about 5.4 feet apart. Toe-ing in the rear speakers (pointing them towards you) should eliminate any sonic gap you're hearing between them.


Sanjay

Unless my math is incorrect does this mean that (the distance between rear speakers) = (the distance from the seated position to the rear speaker) x (.83)?


If I am wrong, please tell me how one figures out the recommended placement of rear speakers (in a 7.1 setup) only 2 factors are known.


Thanks
 

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Quote:
Originally Posted by Kevin12586 /forum/post/12947686


Unless my math is incorrect does this mean that (the distance between rear speakers) = (the distance from the seated position to the rear speaker) x (.83)?

Your math is correct. The easy way to remember the formula: measure to the back wall and multiply by 1.2 to get the rear speaker spread (will give you roughly 60 degrees of separation).


It doesn't have to be exact, since our human hearing is not very good behind us. The wide spread makes it easier to hear the left-vs-right separation of stereo surround-back channels.


Sanjay
 

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Quote:
Originally Posted by Kevin12586 /forum/post/12947686


Unless my math is incorrect does this mean that (the distance between rear speakers) = (the distance from the seated position to the rear speaker) x (.83)?

No, that is not correct. The distance between speakers would be equal (ie x 1.00) to the distance from the seat to the speakers. But that's not a usefull formula to figure out where to put the speakers because you don't know what the distance to the speakers is to figure out how far apart to put them! Sanjay's formula works better.


Ed
 

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Kevin,


My mistake; I misread the math in your post. Ed is correct: you're basically forming an equilateral triangle behind you with the rear speakers (three 60 degree angles).


The distance straight back to the rear wall (not the rear speakers) = the spread of the speakers x .83.


Sanjay
 

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Quote:
Originally Posted by sdurani /forum/post/12949390


Your math is correct. The easy way to remember the formula: measure to the back wall and multiply by 1.2 to get the rear speaker spread (will give you roughly 60 degrees of separation).


It doesn't have to be exact, since our human hearing is not very good behind us. The wide spread makes it easier to hear the left-vs-right separation of stereo surround-back channels.


Sanjay


Got it, now suppose you are limited with the width of the room, for example a room that is 10' wide but 20' long. I know how far apart they will be set (10') but I am unsure of the distance behind the sweet spot. How do I figure out how far back to place the speakers so as to keep the 60 degrees separation?


I hope I explained that properly.
 

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Quote:
Originally Posted by Kevin12586 /forum/post/12954046


How do I figure out how far back to place the speakers so as to keep the 60 degrees separation?

The distance back is 0.87 times the spread between speakers. In your example of 10 feet wide, the speakers would be 8.7 feet behind you.


BUT the rear speakers usually are not spread all the way to the side walls. I think that you would want to put them behind you with a narrower spread than your surround speakers.


Ed
 

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Quote:
Originally Posted by ekb /forum/post/12955993


The distance back is 0.87 times the spread between speakers. In your example of 10 feet wide, the speakers would be 8.7 feet behind you.


BUT the rear speakers usually are not spread all the way to the side walls. I think that you would want to put them behind you with a narrower spread than your surround speakers.


Ed

But wouldn't that take away from the 60 degree separation? Presently I have my sides directly to the side of me and my rears are about 8' back, on the same side wall. I have the rears angled and tilted so the speaker itself is pointing to my head, or just over it.
 

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Quote:
Originally Posted by ekb /forum/post/12955993


BUT the rear speakers usually are not spread all the way to the side walls.

If the goal is to have the rear speakers roughly 60 degrees apart, does it matter which wall they end up on?


Sanjay
 

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Quote:
Originally Posted by Kevin12586 /forum/post/12954046


I know how far apart they will be set (10') but I am unsure of the distance behind the sweet spot.

To get the spread, it was the distance straight back times 1.2. To get the distance straight back, it is spread (10 feet) divided by 1.2.


So in your case it would be 10 feet divided by 1.2 = 8.3 feet behind your side speakers. If you do the actual trig (rather than my simple formula), you'll probably end up closer to Ed's result of 8.7 feet.


Like I said, it doesn't have to be exact; just as long as you're in the ballpark.


Sanjay
 

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Discussion Starter #14
Thanks to Ed and Sanjay for the exacting response. I decided to go with the 60 degree angle, and set the THX asa to 1-4 feet. Tested using RFOM for PS3 in LPCM 7.1 and the rear effects were very accurate (i.e: I could hear someone approaching from the SBL speaker and the audio placement was dead-on). I'd like to test with more true 7.1pcm/dthd/dtsma movies, but selection is limited for now. I'll just use ultra2 cinema with the current blueray 5.1pcm titles, 'cause it gives decent 7.1 playback.
 

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Quote:
Originally Posted by lallen3 /forum/post/12959613


I'd like to test with more true 7.1pcm/dthd/dtsma movies, but selection is limited for now.

Try playing back some 5.1 movies using the Pro Logic IIx Movie mode, which does a better job of extracting stereo surround-back channels than the Ultra2 Cinema mode.


Sanjay
 

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Quote:
Originally Posted by sdurani /forum/post/12956703


To get the spread, it was the distance straight back times 1.2. To get the distance straight back, it is spread (10 feet) divided by 1.2.


So in your case it would be 10 feet divided by 1.2 = 8.3 feet behind your side speakers. If you do the actual trig (rather than my simple formula), you'll probably end up closer to Ed's result of 8.7 feet.


Like I said, it doesn't have to be exact; just as long as you're in the ballpark.


Sanjay

Thanks Sanjay
 

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Quote:
Originally Posted by sdurani /forum/post/12956614


If the goal is to have the rear speakers roughly 60 degrees apart, does it matter which wall they end up on?

If the only criterion is the 60 degrees then no it doesn't matter. But there may be other factors. For example if the rears are dipole or bipole (i know that monopole is usually recommended for rears) you probably wouldn't want them all the way to the sides - plus you'd probably be close to the back corners in most rooms. Also, I think that it's desirable to have the distance from your seat to your surrounds and your back surrounds the same. If you want to keep the 60 degrees, then the rears would need to be positioned narrower than the side walls.


Ed
 

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Quote:
Originally Posted by Kevin12586 /forum/post/12956586


But wouldn't that take away from the 60 degree separation?

No. You can maintain 60 degrees and move the speakers closer together. To do that, the rear speaker would also need to be moved forward. As long as the formulas that were quoted are satisfied, you're good.


Ed
 

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Discussion Starter #19
Yeah, I've been playing around with PLIIx & Ultra2 Cinema modes and I agree that Dolby steers the SBL & SBR in a more lively manner than U2 Cinema. My previous Pioneer Elite receiver let you set the mode to PLIIx+THX which was interesting, but it wouldn't let you turn off the Re-Eq, which I didn't care for, since *some* of my movies would sound way too dry. THX Neural on my Onkyo 805 may be great for XM etc, but for a matrix decoder with a standard stereo or even 5.1 source, I'd have to say it bites...
 

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Does my render (attached) look close to being right for a THX Select 7.1 speaker system? You will have to use your imagination for the speaker mounts in the images sorry. Anything you would do differently?


Does this seem right? 7 Marantz THX MA-500 mono amps, Marantz THX Select2 SR7002, Crystal Acoustics 7.1 THX Select speakers with two 12" subs instead of one.


Room size is close to 20' X 13'. I could toe-in the front surrounds slightly. I'm not sure about moving the other ones to great of a distance or what effect that might have on people in the rear row. If I understand this correctly, I can setup this properly using the AVR.

 
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