Originally Posted by craig john
Well, I'll play devil's advocate for a minute. I was at the Audioholics Show in Clearwater, FL a few weeks ago and Axiom Audio had a room with a 7.1 system using 2 CC's, one above and one below the screen. I asked Ian Colquhoun, owner and founder of Axiom Audio and lead speaker designer, why they were doing that. He responded that it helps to center the audio image on the screen heightwise. With just one center, either above or below the screen, the audio image is pulled higher or lower than the video image. Two centers, one above and one below provides a "phantom" image in the middle, heightwise.
Knowing the "conventional wisdom" on this forum, I raised an eyebrow and sceptically sat down in the sweet spot. Sure enough, he was right; the audio image was higher and the dialogue was better locked to the image. My CC at home is located one inch below the screen and about 8 inches below the tweeter height of the L/R's. I can occasionally notice sounds, especially dialogue that is localized below the screen, so I am sensitive to this. I asked him about the "comb filtering" that is possible with two speakers mounted this way. His reply was that the ear/brain doesn't really "hear" comb filtering. I'm not sure exactly what comb filtering sounds like, but I didn't hear anything bothersome from the two CC's.
Also, the system was using Axiom's new 8-channel amp, so each CC was driven by it's own amp, eliminating the problem of using the same amp for both speakers.
I would want to spend more time using such a system before I would outright recommend it to someone. Nonetheless, I was surprised that the conventional wisdom of this forum that we should never use two CC's was not absolutely confirmed, as I expected it would be.
We have the same set up (above and below) and our last home theater had a similar one. We have a 110 inch projection system and seating is about 12 feet from the screen. The sreen is a DaLite High Power, which is not perforated. To anchor the dialog to the screen (without an acoustically perforated screen), I decided to go high/low.
I have one of the centers under the screen at floor level. It is angled up slightly (with a laser pointer) to aim the tweeter at ear level. I have a second center above the screen with the tweeter aimed down to ear level.
To solve the balance (and AVR amp load) problem, I purchased an separate stereo amp. (HK). I split the center channel preamp output of the AVR (Pioneer SC35) with an rca "Y" and send the two identical signal(s) to the amp. I turn on the amp with a 12 volt trigger from the AVR , so when it powers on and off the amp does as well. So, I feed each of the center channel speakers with the R/L output of the stereo amp. I balance the total 7.1 system with the AVR MCAC. It "sees" the total sound energy coming from the two centers as the "one" center channel. The trim adjustments (volume controls) on the amp allow me to tweak the output of each center speaker "channel" to bring the phantom image of the dialog to the upper third center of the screen. It works like a charm.