Phil Pugliese

I have tp set up my system different in my LR. I have a square room and I have to have the TY in the corner. In the oposite side I will have a corner couch. my question involves my rear speakers. Now I am using a Sony Pro-Logic surround vs. Dolby Digital, so the rear is actually mono. Can I use a single rear speaker such as a center channel for the back? If so, how would I run the rires from the amp. I know this is not deal, but I don't have much of a chioce. If anyone has a better idea (other than devorce), I am open.

Brian Shannon

Even though the rear is "mono" in a pro-logic setup you still cannot use a single speaker because there is seperation and balance between left and right.

You would need to use two and perhaps some wireless speakers would do the trick. Otherwise Monster Cable makes flat cable.

Good luck.

stevevt

By definition, the fact that the rear signal is mono means that there is no difference between the signal reaching the rear left and rear right.

It's preferable, but not necessary to use two speakers. If you use one, just use the output from either the back left or back right (not both), and use your test tone to get the level right.

Brian Shannon

I disagree.

There is a HUGE difference in the way the signal reaches the listeners ear and that is why a single speaker would not work.

"Not so obvious is that there is also no theoretical loss of separation between the center and surround signals. Since the surround signal is recovered by taking the difference between Lt and Rt, the identical center channel components in Lt and Rt will exactly cancel each other in the surround output. Likewise, since the center channel is derived from the sum of Lt and Rt, the equal and opposite surround channel components will cancel each other in the center output.
The ability for this cancellation technique to maintain high separation between center and surround signals requires that the amplitude and phase characteristics of the two transmission channels be as close as possible. For instance, if the center channel components in Lt are not identical to the ones in Rt as a result of a mismatch in channel balance, center information will come out of the surround channel in the form of unwanted crosstalk."

http://www.dolby.com/tech/whtppr.html

"In order to get a feel for how much separation is needed to prevent the correlated crosstalk in a surround system from disrupting image placement, you can try the following experiment with a two-speaker stereo system. Select any signal source, music or dialogue, and play it in monaural from both speakers. While seated in the normal listening position, have someone turn the balance control completely to the left, so that the right speaker is off. Then, while the control is rotated slowly toward the center position, note the point where you first hear the right speaker come on, or where you can detect that the image has moved away from the left speaker. If you then unplug the left speaker, you will hear how loud the right speaker had to be to make this happen. Depending on the angle between the speakers and the listener's acuity, the right speaker will be only about 10 to 20 dB lower than the left one, substantially less than what is needed to prevent unrelated signals from interfering with each other.

The results of the above experiment correlate with the separation needed between the left and right channels of a surround system; somewhat less is needed between the center and the left or right channels since the distance between them is only half as much. The separation map for a typical Dolby Pro Logic decoder is provided in Fig. 11, showing that about 30 dB of separation is available between any pair of channels. It should be noted that the results of the above experiment represent the separation needed for a purely dominant sound source. The map figures similarly represent separation measured with a purely dominant, steady-state test tone signal"

http://www.dolby.com/tech/ddfaq_figu...AQ.page11.html

DigIt

I am not clear on why the placement of the couch precludes the use of two speakers. Reason?

Phil Pugliese

fair question...The ideal seat position will be in the oposite corner, If I put the speakers left and right, I will actually be sitting behind the two rears. If I do a single mono, I can put it deap in the corner.

DigIt

Ah, makes perfect sense. Well, theoretically speaking, if you placed the speakers high enough and aimed them to fire at each other over the couch, even if you are "behind the crossfire" you should still get a satisfactory surround effect. Movie theaters are essentially set up this way, with some speakers being in front of (albeit some behind) any one of the theater seats. Also, dipole speakers essentially fire the sound forward and backward, but not directly above or behind the listener. All you're really trying to do is create a diffuse surround sound area.

I would experiement with this type of placement before going with a single center. If you do choose to do that, though, you should be able to find a center speaker with two sets of connections (one for each driver), allowing you to connect both the rear-right and rear-left speaker wires to the same speaker.

Also, you could try placing a surround speaker behind each half of the couch and pointing upwards, which I think would be better than a single center speaker mounted on the wall. Is there clearance behind the couch?