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why does 5.1 sound better than 6.1? (1 Viewer)

Rob Michaw

Stunt Coordinator
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May 2, 2000
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A very broad statement, but I will explain. I own an Integra 7.1 receiver capable of reproducing THX EX and DTS ES (albeit matrixed). My receiver also has power for one rear speaker, or pre-outs for 2. I am running JM Labs Cobalt 816s up front, the cc800 for the center, and 2 PSB 1Bs as rears (I am replacing soon with sr800s in the rear). I have one speaker that I run as the EX rear speaker. This is an old Cerwin Vega bookshelf speaker I have had kicking around for years. My surrounds are 5 ft away from me, and the rear speaker is 10 feet away. I have the levels just about right, as well as delay settings.

When the EX is engaged with non EX encoded material, the surrounds are very weak, almost as if they are not on. When I disengage the EX, the volume and depth of the surrounds really opens up and fills in the space behind me as if the speaker was on. I haven't tried the rear speaker off while listening to THX EX or DTS ES encoded discs (as I was just thinking about writing this now), but is there any reason why this is happening? I was expecting the rear speaker to fill in the hole a little and make a fuller sound, not thinner.

Any ideas?
 

DanielSmi

Second Unit
Joined
Mar 20, 2002
Messages
455
Sometimes that is known to happen with THX-EX which is one of the reasons THX created THX ULTRA2 processing which solves this problem but I believe you have to use 7 speakers not 6 for ULTRA2 to turn on.

Daniel Smith
 

AaronBatiuk

Second Unit
Joined
Aug 23, 2002
Messages
333
As Daniel suggested, try using 7 speakers, not 6. Even though both DD-EX and dts-ES decode 6 channels, THX, Dolby, and dts all strongly recommend using 7 speakers, that is, using two speakers in the back instead of just one, for the extended surround rear channel.

I assume that the Cerwin Vega is one of a pair. If so, use both. If not, get (borrow) a pair form a friend. Be careful if connecting two CV's to a single amp channel on your receiver. Many CV's are rated at 6 or even 4 Ohms. If they are less than 8 Ohms, wire them in series instead of in parallel (+ of one speaker to amp +, - of the other speaker to amp -, then the remaining two +/- speaker terminals to each other). If they are rated 8 Ohms and your receiver can handle a 4 ohm load, wire them in parallel.

Something else to try: reverse the polarity on the surround back speaker. It may be out of phase with the other two channels, which could cause the rear soundstage to collapse like you seem to be experiencing.
 

Michael Reuben

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Feb 12, 1998
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Real Name
Michael Reuben
When the EX is engaged with non EX encoded material, the surrounds are very weak, almost as if they are not on.
This is precisely why EX (the basic variety) should not be engaged with standard 5.1 material.

An EX decoder extracts the rear center using the same approach that Dolby ProLogic uses for extracting a front center -- sounds that are equally present in the left and right are routed to the center. Now, in a track that's been mixed for EX, the sound designers know which sounds they want to route to the center, and they put those sounds equally in the left and right rears. Sounds that are supposed to remain at the left or right are weighted toward that speaker so that the the EX decoder leaves them there.

Many 5.1 soundtracks don't provide much differentiation between the left and right rears, even though they're discrete channels. When you engage EX decoding on such a soundtrack, the sound will collapse toward the center, just as you've described.

M.
 

Jeff Adams

Screenwriter
Joined
Dec 13, 1999
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Very good explanation Michael. When I first got my receiver I was watching everything in EX or ES mode, now I have gone back to wathing 5.1 in normal 5.1 mode and only watching EX and ES encoded movies with the rears on. I too feel that 5.1 material does not sound as good on EX and ES mode compared to normal 5.1 mode.
 

Kevin C Brown

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Aug 3, 2000
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There are some receivers and pre/pros out there with 6.1/7.1 modes specifically meant for use with "normal" 5.1 DD/DTS soundtracks too. Prevents the collapse of the rear soundstage that can happen with EX/ES. Rotel xS, Outlaw's (Cirrus') CES modes, Logic 7, Denon's "widescreen" mode (or something), etc.
 

Rob Michaw

Stunt Coordinator
Joined
May 2, 2000
Messages
132
Thanks for the replies. I have known that 5.1 is not "made" to be played 6.1, but in early magazine reviews, I remember some reviewers commenting on the fact that this can enhance the movie. I assumed that it meant so across the board. I was wrong. I am also glad to see that others have found the same as I have, so I will not start questioning if my setup is somehow wrong.

Thanks.
 

Kevin C Brown

Senior HTF Member
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Aug 3, 2000
Messages
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Rob- I give you credit. :) A lot of people blindly (deaf-ly?) engage EX/ES decoding *believing* it must be better because it's newer. You actually listened to the effect on 5.1 material and heard for yourself, sometimes it works, and sometimes not...
 

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