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Discussion Starter · #1 ·
My room layout for my surrounds and back surrounds is as follows. My back wall is 12 feet wide and my couch is against the back wall. By dipolar surrounds are on each of the sidewalls approximately one foot off the back wall (limited as each sidewall is only about 3 feet wide). My left surround speaker is about 2 feet from my couch and my right surround speaker is 3 feet from my couch. I recently added a spare center channel speaker that I had lying around as a surround back speaker on the floor behind the couch facing up. Overall I'm pretty happy with the effect of the surround back speaker despite it's less than optimal location.


My question is that given the relatively small width of the back wall would I benefit from going to 2 surround back channels instead of 1. If I add 2 surrond back speakers my concern is that they will be too close to the left and right surrounds.


My setup consists of a Yamaha RX-V2400 receiver, Polk RTi70 mains, Polk CSi40 center, Polk FXi50 dipole/bipole surrounds and Polk CS245i surround back (temporary).


So I guess my question is whether to go with 1 or 2 Polk RTi28 or RTi38 speakers. (If I stick with just one would I see a noticable improvement using a bookshelf speaker such as the RTI28 or 38 instead of the center speaker I'm using now?).
 

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Another thing to factor in your decision is that it is easier to get a pair of surround speakers to act as your 6th and 7th rear center speakers as opposed to breaking the pair and just trying to buy one speaker. We have a 6.1 receiver so we wound up buying another center to use for that 6th speaker since it's hard to find a single satellite surround speaker. Most vendors only sell them in pairs.
 

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If you look around for references, and I didn't believe this at first either, there is a psycho-acoustical effect whereby if the human brain hears a sound directly behind you, it can mistake it for coming from directly in front of you. 2 speakers back there vs 1 helps to eliminate that. That's why for example, Logic 7 supports 5.1 and 7.1 speaker setups, but not 6.1.


I personally had an 18 month odyssey to go from 5.1 to 6.1 to 7.1. If you can do it, I highly recommend skipping 6.1 and just do 7.1. You get better differentiation of left and right in the back of the room with 7.1 vs 6.1. But you need DSP to support that. Logic 7, DPL IIx, and to some degree, THX Ultra2. Yamaha actually has some of the best DSP vs Sony, Pioneer, Onkyo, etc, IMO.


One more thought, and this may seem sacriligious to some :), is that you can move the surrounds slightly forward of the listening position, if that works in your room, to give them "space" vs the rears and still get a quite acceptable sound field.
 

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Go with 8-channels, if you can. You get better panning and independent hard pans between the sides and rears with ambiance extraction. I am a Lexicon Logic 7 user also, it is more dramatic than my old 5.1 setup.
 

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HTG: 8 = 7 + 1 => 7.1?
 

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Yes. Many who go with 7.1 (eight channel, the 7 plus the LFE) go with an additional sub to get what some call 7.2, but in theory it is still 7.1 as Bass Management implents the sub in mono. The THX guy Tom Holman demo'd a 10.2 setup at CES a few years back. It had height channels.
 

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Discussion Starter · #7 ·
Kevin,


My main concern with going to 7.1 is that the left back surround will only be about 2 feet away from the left surround speaker in order to maintain the 4 feet of distance between the 2 surround back speakers (as recommended by the Dolby site). I'm worried that having these two speakers (left surround and left surround back) that close to eachother will ruin the soundstange.


12 ft

___________

| _ _ |

| [ ] | 2 ft


This is pretty much what my speaker placement will look like with 2 surround back speakers. The [ are the left and right surrounds and the _ are the surround back speakers. Would I be losing the advantages of a 7.1 setup by bringing the 2 back surrounds closer together than 4 feet?


Per the above diagram the right back surround is about 1.5 ft farther from the right surround than the left surround back is from the left surround. On the right side of the couch there is an end table so there is no option to center the couch in order to spread out the speakers.
 

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What about keeping your rear surrounds together?


And BTW, why is it called 7.1 when there are only six discrete channels (plus the LFE)? The two rear surround speakers are mono, not stereo.
 

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I know Lexicon is doing an 8-channel (7.1) output on their newer pre/pros. Although nothing is encoded in discrete 7.1 with stereo rears, some companies like Lexicon use ambiance extraction that creates stereo to not only the sides, but also the rears, The side and rear speakers on either side may be playing the same material, or they may not. In situations where you have a "hard panned" sound (like a door slamming), in the left surround channel this will be played back over both the left side and the left rear. However, if there is panning or movement of the sound from one surround speaker to the next certain modes can steer these sounds independently between all four surround speakers. This is the main reason I use Lexicon and it's Logic 7 mode.
 

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EVT, well... The THX Ultra2 recommendation actually includes that the rear speakers can actually be side by side.


But I agree that keeping them further apart helps to differentiate what's going on in the back of the room between right and left. I don't know. That's a tough one. Any way you could set up a temporary solution and try out 7.1 vs what you have for 6.1 now?
 

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Quote:
Originally posted by beowulf7
why is it called 7.1 when there are only six discrete channels (plus the LFE)? The two rear surround speakers are mono, not stereo.
You are correct: the X.x nomenclature is usually used to describe the number of discrete channels being delivered, and currently there is no consumer 7.1-channel media available. Most of the time when you see "7.1" being used, folks are referring to the speaker set-up.


Why use 7 speakers when the surround-back channel is mono? Because of a psychoacoustic phonemenon called back/front reversals, where sounds along the centre line can appear to momentarily switch location. This usually occurs with a single speaker behind the listener, where our human hearing is pretty weak, occasionally making those sounds seem like they're coming from in front.


Reversal is a well researched & documented problem that has an easy solution: simply use two speakers, spread well away from the centre line. This is the reason why Dolby and DTS and THX all recommend using two surround-back speakers for the mono surround-back channel on EX/ES soundtracks. Ever wonder why that was the only channel where it is recommended that two speakers be used? Now you know.


Of course not all 7.1 systems run the two surround-back speaker as dual-mono. If you are using Lexicon's LOGIC7 processing or Dolby's new PLIIx mode, then you will have 7 independent channels of sound with no two channels being dual-mono. The source material may not be 7 discrete channels, but the result of the processing is 7 distinct channels; each playing individual information and each individually time aligned. As PLIIx starts showing up in more and more receivers, the two surround-back speakers will be used less and less as dual-mono.


Best,

Sanjay
 

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Quote:
Originally posted by sdurani
You are correct: the X.x nomenclature is usually used to describe the number of discrete channels being delivered, and currently there is no consumer 7.1-channel media available. Most of the time when you see "7.1" being used, folks are referring to the speaker set-up.


Why use 7 speakers when the surround-back channel is mono? Because of a psychoacoustic phonemenon called back/front reversals, where sounds along the centre line can appear to momentarily switch location. This usually occurs with a single speaker behind the listener, where our human hearing is pretty weak, occasionally making those sounds seem like they're coming from in front.


Reversal is a well researched & documented problem that has an easy solution: simply use two speakers, spread well away from the centre line. This is the reason why Dolby and DTS and THX all recommend using two surround-back speakers for the mono surround-back channel on EX/ES soundtracks. Ever wonder why that was the only channel where it is recommended that two speakers be used? Now you know.


Of course not all 7.1 systems run the two surround-back speaker as dual-mono. If you are using Lexicon's LOGIC7 processing or Dolby's new PLIIx mode, then you will have 7 independent channels of sound with no two channels being dual-mono. The source material may not be 7 discrete channels, but the result of the processing is 7 distinct channels; each playing individual information and each individually time aligned. As PLIIx starts showing up in more and more receivers, the two surround-back speakers will be used less and less as dual-mono.


Best,

Sanjay
Thanks! :cool:


I haven't heard much of PLIIx since ProLogic II is still "relatively" new, but it seems like the x-factor going to sound sweet. So you'd recommend a quasi-7.1 over 6.1 if someone wnated a rear surround and had the space for two rear speakers? I think I might just do that when I build my HTS. Thanks again for the info.
 

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Quote:
Originally posted by beowulf7
So you'd recommend a quasi-7.1 over 6.1 if someone wnated a rear surround and had the space for two rear speakers?
Exactly. And if you don't have the space for two rear speakers, then I'd recommend sticking to a 5.1 system. Personally, I wouldn't use a 6.1-speaker set-up.
Quote:
I think I might just do that when I build my HTS.
Remember to spread the rear speakers at least 30 degrees away from the centre line. This will become more important as PLIIx gains popularity; you'll need the separation between the speakers to appreciate the stereo rear channels.


Good Luck,

Sanjay
 

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Quote:
Originally posted by sdurani
Exactly. And if you don't have the space for two rear speakers, then I'd recommend sticking to a 5.1 system. Personally, I wouldn't use a 6.1-speaker set-up.
Maybe it's just me but I have never had issue distinguishing sound coming from the 6th rear channel on my system. I can tell you that going from 5.1 to 6.1 has been incredibly enjoyable and has added a new dimension to my listening. 5.1 vs 6.1 is night and day(when listening to 6.1 discrete).


Everyone is different. My advice would be to goto a place where you can experience 6.1 a see what you think. That is the only way to know for sure.
 

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One interesting DPL-II content that I've found pretty neat to demonstrate how straight DPL-II 5.1 compares to Logic7 processing of that same signal is the sound-test segment on the Star Wars Rebel Leader II and III video game titles from Lucas on the Nintendo GameCube.


Basically, it has a Tie-Fighter circling you continuously. It is rendered on the screen as it passes in front of you and just sound when it is circling around beside and behind you. Because it is continuously doing it, it is very easy to do A/B listening tests and speaker position adjustments.


Once you got your system set up right, the effect is incredible. The effect during certain stages of game play is almost critical as you can "audibly" detect where the enemy is so you can go after it.


The only odd thing is that sound doesn't travel through the vacuum of space :)
 

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Quote:
Originally posted by Chuck_IV
Maybe it's just me but I have never had issue distinguishing sound coming from the 6th rear channel on my system.
How would you know? The nature of front-back auditory confusion is such that the listener mistakes some sounds coming from the rear and hears them as coming from the front. This doesn't happen to every sound, but it happens often enough that your ability to accurately localize in the front or rear is significantly compromised, and you are not even aware of it when it's happening. Adding a second rear speaker eliminates the problem entirely, which is why THX, DTS, Dolby, Lexicon, and Meridian all recommend 7.1 speaker configurations as optimal.


Cheers,

Philip Brandes
 

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"Adding a second rear speaker eliminates the problem entirely, which is why THX, DTS, Dolby, Lexicon, and Meridian all recommend 7.1 speaker configurations as optimal." (Philip's words)


This is true.
 

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Quote:
Originally posted by Philip Brandes
How would you know? The nature of front-back auditory confusion is such that the listener mistakes some sounds coming from the rear and hears them as coming from the front. This doesn't happen to every sound, but it happens often enough that your ability to accurately localize in the front or rear is significantly compromised, and you are not even aware of it when it's happening. Adding a second rear speaker eliminates the problem entirely, which is why THX, DTS, Dolby, Lexicon, and Meridian all recommend 7.1 speaker configurations as optimal.


Cheers,

Philip Brandes
??? Because, the sounds I hear come from the same place, no matter where I sit. Whether it be sitting in the optimal location, where the 6th speaker is directly behind me or off to the side, the same sounds resonate from the same locations. I'm not saying 7.1 is not optimal, but I am saying their isn't as much issue with 6.1 as some like to believe.


I know what I am hearing and not hearing and where it is coming from. That is why I say everyone is different and they need to find out for themselves and not to rely on anything but their own two ears.
 

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Or one ear.
 
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