Double, or virtual, center channel

[soiset]

Currently, I have the fantastic 34" Sony XBR960, with a CS350LS on top of it, but eventually I plan to install a real theater with a projector (I need to see 1080p under $4000).

Because HT screens aren't perforated, the center speaker cannot actually be at the center of the screen vertically. So I want to try a CS350 above and below the screen, with each angled down and up, respectively, toward the listening position.

I understand that this is called a "virtual" center, as opposed to a "phantom" center, which made from left and right speakers fed identical info.

Does anyone have any experience with this kind of a setup?

[Tour2ma]

Never heard the term "virtual" applied to the set up, but fine by me... it needed a name.

Yup twin CS400's above and below my measily 36" Toshiba CRT. The dialog with one on top was always "pulling my ears up"... I found it distracting.

Folks will warn you about "comb effects" from their interaction leading to nulls from them cancelling each other out at certain frequencies. It is a real phenomenon and might occur. However, I have not encountered it and it is resolvable by playing with the twin centers' distance from the back wall, and thus their distance from you.

Have at it...

[Midnite Mick]

I watched a movie at someones house on a screen with the center channel behind it atop a big screen TV. When I asked him what he does with the center channel as I saw him setting it up. He said that the screen is periferated. Hmmm I wonder if he made it himself then as it sounded fantastic?

Mike

[soiset]

Well, I didn't think HT screens were ever perforated, because of their smaller size, but maybe I am wrong. I would still think that you'd end up with lots of diffraction from that, though.

Tour2ma, how are you driving your centers?

... and why don't you sell me your 350, since it is so inferior to the 400? ;)

[Tour2ma]

LOL... I just might. But we can probably work out an audition for you. Are you/ we making a Beaumont run?

I had an extra couple of amp ch's laying around for the second 400... I knew there was a reason I needed 10 of them. ;)

[soiset]

'Fraid not. Jose has apparently sold everything.

Just let me know when you get sick of that pathetic 350 you have!

[Larry Chanin]

Hi,

Yes, I have two center channels set up as you describe. Click on the link in my signature for details regarding my home theater.

The following thread may also be of interest to you.

Dual Centers for Front Projection?

If you have specific questions not addressed in the above links, I'd be happy to attempt to answer them.

Yes, perforated screens for home theaters are available. Refer to the links below. From an acoustic point of view they are ideal. In addition to permitting the location of speakers in the perfect location behind the screen they eliminate a large acoustically reflective surface in the front of the home theater. As you may be aware, acoustically the object is to have the front of a home theater highly absorbent. Having a large non-perforated screen is at odds with that objective.

Acoustically Transparent Screens from Stewart Filmscreen

Acoustically Transparent Screens from Screen Research

Larry

[soiset]

All right, that does it! Tour, sell me that damned speaker!

[Larry Chanin]

Hi,

Here's an other thread in which the pros and cons of vertically stacked centers was discussed.

How's this for a center ch. solution

Larry

[soiset]

Seems like any problems with comb filtering, etc., could be eliminated by a simple processor: one that sets the apparent stage in the center of the screen, like a sort of stereo effect. Ever heard of such?

[Tour2ma]

All right, that does it! Tour, sell me that damned speaker!

You only want the one? :D

In case you did not notice, Larry built himself one helluva a HT...

How ya doing, Larry? Getting your 2Q06 post out of the way early?

[soiset]

Oh, I noticed, with subsequent envy...

[soiset]

Hi,

Yes, perforated screens for home theaters are available. Refer to the links below. From an acoustic point of view they are ideal. In addition to permitting the location of speakers in the perfect location behind the screen they eliminate a large acoustically reflective surface in the front of the home theater. As you may be aware, acoustically the object is to have the front of a home theater highly absorbent. Having a large non-perforated screen is at odds with that objective.

Acoustically Transparent Screens from Stewart Filmscreen

Acoustically Transparent Screens from Screen Research

Larry

Didn't know that; thanks for the tip! I'll look into those screens for my eventual theater.

[okiepolkie]

Draper and Da-Lite offer acoustically transparent screens, but I know they are usually a little more costly than the standard screens. For reference in price, take a look at the two the respective websites. Both have MSRP's detailed for each screen. The MSRP isn't much different than the actual retail price in many instances. There just isn't much of a mark up for dealers on screens.

[Tour2ma]

Oh, I noticed, with subsequent envy...

LOL... I think we might be able to work something out. I also have a spare CS400, if you'd like to audition it as well.

[Larry Chanin]

Seems like any problems with comb filtering, etc., could be eliminated by a simple processor: one that sets the apparent stage in the center of the screen, like a sort of stereo effect. Ever heard of such?

Hi,

I'm not sure exactly what you're referring to when you say "sets the apparent stage in the center of the screen". When a portion of a soundtrack is mixed to center a sonic image horizontally in the soundfield, such as during normal dialog, the stacked centers will center the sonic image both horizontally and vertically on the screen. This is achieved for the entire audience, not just those who are sitting on-axis. Comb filtering doesn't prevent this from happening. What it is supposed to do is slightly blur the sonic image, making the imaging less precise. The reason I say "supposed to do" is that my ears aren't good enough to discern a problem.

Some professional home theater designers use expensive processors that can add a delay to a signal. The application is used when multiple sets of side surrounds are being installed in very large home theaters. (In theory, playing the same surround signals out of two pairs of side surrounds could also create comb filtering.) I suppose that if stacked centers couldn't be placed equidistant from the listeners, then such a delay processor might be of some value for enthusiasts who were seriously concerned about minimizing comb filtering to a single row of listeners.

However, the problem with comb filtering is complicated (assuming you believe it to be a serious problem) when a home theater has multiple rows. Unless the ears of the audience in both rows are centered vertically on the screen, it is not possible to have the listeners' in both rows equidistant from both centers. You can either make the first row equidistant or the rear row, not both. Many home theaters, including mine, have a rear seating platform whose purpose is to preserve the line of sight of members in the rear row by raising the seating. Therefore, it is not possible via speaker placement to maintain this equidistant speaker placement to both rows. A delay processor wouldn't help either. For instance, if speaker placement was used to make say the front row equidistant from the centers, then the rear row would not be equidistant. Now, if a processor was used in an attempt to delay the signal from the more distant speaker, it would bring the rear row into time alignment, but unfortunately it would throw off the time alignment of the front row which was perfect prior to using the processor.

Larry

[Larry Chanin]

In case you did not notice, Larry built himself one helluva a HT...

Hi Bruce,

Thanks very much for the compliment.

How ya doing, Larry?

I'm doing fine, how are you doing?

Getting your 2Q06 post out of the way early?

Yes, absolutely. I'm a firm believer of quality over quantity. ;)

Regards,

Larry