3 channel setup question

[Coytee]

I was listening to the Khorns & Al's newly installed ES networks yesterday... then a thought/question hit me:

If you have the mixer box (forget what it's called) that allows for a 3-channel setup, if you turn balance controls all left or all right, what happens to the center channel?

Since (my understanding) the center channel is +R+L, do I presume the center channel will become equal to which ever side is left at full volume?

I seem to recall that the center can be subtractive also, though I don't recall how. If it's the subtractive version, then what happens...if anything?

Once you answer this, you may return to the SET battlefront

[mark1101]

I have one of Dr. Bill's center channel boxes that was built to the PWK spec for achieving a composite center channel. I recently began using it, and I am really satisfied with how it works.

However, I never did the little test you mention above. I will tonight though and report back.

Thanks

[mark1101]

What I found is that when the balance control is all the way left, to the best my ears can tell me the center channel seems to be left information only. Same thing when the balance is turned right. The center speaker and the right speaker sound exactly the same to me.

It's a little trickly to say that a heresy © is playing exactly the same information as a cornwall (L/R), especially since they are powered by different amps to boot, but I think that is really what is going on.

[PrestonTom]

I also have an additive center channel box. I highly recommend them. You can't lose since it is only about $10 worth of parts and easy to assemble.

If the energy is identical (correlated) in the Left & Right and you add them there will be 6 dB increase if it is not the same (uncorrelated or energy only in one side) then there will only 3db increase (at most). The complication is that the center should not be set at the same level as the L & R. You are only trying to "fill in" the image in the middle. So it is best to back off a bit.

The output of the center should be subtle. If it is trurned up too much the stereo panorama will no longer be very wide. Additionally since the center channel is usually not as high quaility as the L & R speakers, you do not want its voicing to dominate. The issue of how much to attenuate the center takes some experimentation. But it is a fun experiment.

In answer to you question, if you turn the balance to the left speaker, only the Left and Center will be heard (and the Center will not be as loud).

Good luck,

-Tom

[Tony Reed]

I seem to recall PWK saying that the center speaker should be somewhere around 3db down. That sure doesn't sound like much.

Tony

[mark1101]

The center channel box I have was built by Dr. Bill who is on this forum. I'm sure he's around here somewhere. There is also a thread on this forum that contains one of PWK's papers on center channel.

Supposedly the box I have has the exact same circuit PWK used. It has a pot to control the volume of the center channel output. I feed that signal into another amp that drives a pair of stacked heresys. I play the center channel just loud enough to remove the "hole".

I have my cornwalls 32 ft. apart and the room dept is only about 15 ft. So I can't get back far enough. But having the center channel greatly improves the situation.

[Mallette]

Correct me if I am wrong...but if you are using a Cornwall between two Klipschorns, are you not already starting 3db down? When I used my DynaQuad to get a passive, mixed center to a Cornie, I felt I really needed just a couple of db more there. Using an active center where I can boost it slightly, I am much more satisfied with the imaging.

Dave

[scriven]

After I got mine set up the way I liked I measured it. The center was running 3db below the mains.

[PrestonTom]

Dave,

In my case (Cornwall between 2 K-Horns): I have not measured what the level is. The 2 types speakers have different efficiencies and the center amp is a different model. The point is that the level of the center does not need to be loud since the L & R are doing the work. My discussion was meant to shed some light on what the level from the center might be if it powered by a signal that was correlated or uncorrelated at each channel.

-Tom