Proper configuration for 8 speakers with 4x8 matrix processor

[rcohen]

We're in the process of setting up a theater room for our new office. The purpose of the room is to impressively demo our video games, with immersive sound.

The room is 32' long, and 18' wide. In order to provide a seamless sound field, we have 8 speakers:
Two in front, on either side of the projection screen.
Two in back, opposite the front speakers.
Two each, on the left and right sides, evenly spaced on those walls.
(This is in addition to a couple subwoofers.)
The conference table is 18' long, and 5' wide.

From the top, it looks like this:

........L2..........L1........
RL............................FL
.......[conf table]........| (projector screen)
.......[.............]........|
RR............................FR
........R2.........R1........

The input signal is 4 full range channels.
Our preamp routes the lower bass to the subs.
For 5.1 inputs, we have the preamp set to phantom center.
We're using a 4x8 matrix processor and 8 channels of amplification to feed our 8 speakers.

What I'm wondering is, what is the best way to configure the levels, phase, and delay of the matrix processor to provide the most immersive sound?

Should the left and channels just mix the left two inputs, or should they mix in the right inputs, with phase reversed?
For example:
L1 = 67% FL + 33% RL
or
L1 = 67% (FL - FR) + 33% (RL - RR)
or
somewhere in between?
or
something else?

Should the speakers be time aligned at the screen, or at the middle of the room?

I'd really appreciate advice, or any helpful links or literature. I've had a hard time finding much, which is surprising, since this seems like movie theaters would have similar issues.

Thanks,
Rob

 

[Johnd]

You have done a good job displaying the room, layout and system, but failed to mention the size of the conference table. Obviously, the bigger the table, the further some will be at any given time from some of your equidistant speakers.

And there's the rub. You have probably had a difficult time finding literature on this type of layout because it is far from ideal for surround sound.

That being said, I see no reason why any speakers should be set out of phase, and, assuming listeners will generally be all around the table (as opposed to generally at one end or the other), I think the speaker levels out to be set the same to one another given your current layout.

 

[rcohen]

Here are the exact dimensions:
Room: 32'x18'
Conf table: 18'x5'

I know that the conference table isn't ideal for acoustics, but it is ideal for the purpose of the room - presentations. It allows us to interact with our clients. It is conceivable that we could have multiple presets on the DSP, a general one for any seat (if the clients are spread out), and presets tuned for where the client is sitting (which we could select by remote control).

The reason I was considering negative phase was try to isolate the left and right signals, but that may do more harm than good. So, you think sticking with positive phase will provide more immersive sound?

 

[Johnd]

What kind of signals will you primarily be sending? Mono, stereo, 2.1, 5.1?

 

[rcohen]

To clarify, I didn't mean inverting the phase of any of the speakers, I meant possibly inverting the phase of some of the input channels in the 4x8 mixing matrix (the minuses in one of my potential mixing equations).

 

[rcohen]

What kind of signals will you primarily be sending? Mono, stereo, 2.1, 5.1?

Either 4 channel or 5 channel (full range, no LFE). 5 channel will be converted back to 4 channel by the preamp, prior to the 4x8 matrix DSP. This is for video game surround sound.

 

[AVRat]

What sort of pre-amp are you using? In your setup, a 7.1 channel capable pre-amp should provide ample processing for an immersive presentation of your software. In the vast majority of sytems like this, a Y-adapter is used to split the side-surrounds. Only a true 8/9 channel processor will do what you're looking for.

 

[rcohen]

We have the equipment to do whatever processing. My question is how to configure it for our setup.

If it helps, the DSP is a Shure P4800.