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  1. #1
    Senior Member Andrew Robinson's Avatar
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    Sep 2011
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    To Diffuse Or Not To Diffuse - A Note On Surround Channels

    I use in-ceiling loudspeakers from Noble Fidelity (L-85 LCRS) as my rear channels. I only have a 5.1 setup (4.1 actually, no center) so I only have a pair of surround/rear channels. In 5.1 setup it's advised that the rear speakers be placed in line with your listening position and not behind as some may think; behind is for back channels in a 7.1 type of setup. But there are a variety of theories regarding rear channels with regards to diffusion. When I installed my Noble Fidelity in-ceiling loudspeakers I did so per their request, which was to aim the 15-degree angled driver not at my listening position but instead at my side walls. Noble suggested this to give me a broader, more diffused surround sound presentation, the idea being the sound would bounce off my side walls and thus off my back wall giving me more of a 360-degree surround sound field. The theory is sound for they're NOT the only ones attempting to make 2 speakers sound like 3 if not 4 by using sound diffusion or reflection. Hell, di-poles do this as well. But does it work?

    There's no denying that reflecting or diffusing sound will create a sense of space and ambiance, but are we doing it in an attempt to trick our brain into thinking something other than the truth? The answer is yes -at least, in my humble experience. Recently I turned my rear channels 'round so that the drivers were now pointed at my listening position versus away, into the side walls. Because the relationship between our ears and our brain is so complex, sitting in the middle of a stereo-esq setup, albeit with rears, your mind fills in a center image. The center image in this case appeared to be behind me, where as when the sound was diffused I had really good lateral dispersion but it never fully "connected" behind. Furthermore, I had a stereo image between my right rear and right front and likewise on the left side too, meaning I retained my solid lateral dispersion but now had stronger rear imaging. So, when in doubt, in a 5.1 system, keep your surround channels in line with your seating position and point those suckers at your main listening position. They can be higher of course, but I wouldn't recommend behind, or firing into a wall. As for di-poles and the like, eh.

    What say you?

  2. #2
    Senior Member
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    Nov 2001
    Location
    Florida
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    232


    I initially installed in-ceiling speakers (so long ago I've forgotton the brand) as surrounds for my first attempt at a 5.1. Well, the in-ceiling speakers are still up there, but only because I don't want to deal with two gaping holes in my popcorn ceiling. The in-ceilings haven't so much as sniffed an audio signal in ten years.

    I currently have a bad case of upgradeitis and plan to go all the way to 7.1 by installing a pair of wall-mounted Polk FXI A4 surrounds. The FXI A4s allow (via toggle switch) switching to either bipole or dipole operation to direct the sound at the listener or to diffuse the sound into the room. I just hope that they work as advertised because cheap, they are not.

  3. #3
    Administrator Tracy Rainwater's Avatar
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    Sep 2003
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    18,177


    Dave, in-walls and in-ceiling speakers are a totally different animal now. I would rip those old ones out and give the Noble Fidelity in-ceiling speakers a shot. Any speaker that Andrew would be willing to cut a hole in his ceiling for, has to be good.

  4. #4
    Senior Member
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    Nov 2001
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    Florida
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    Tracy - I don't doubt it, and I may get around to trying different in-ceiling speakers someday, but for now I am going to follow Andrew's recommendation "keep your surround channels in line with your seating position and point those suckers at your main listening position".

    BTW, those old ceiling speakers that I installed did have aimable (probably not a real word) directional tweeters but the sound field always went straight down in a narrow cone, regardless of the tweeter position or audio setting. Utimately, I gave up as one had to be sitting directly beneath one of the in-ceilings to hear any sound effects or music. Forget about picking up anything from the opposite in-ceiling speaker. I believe that the concept had merit but was doomed by inadequate speaker technology and by the fact that I have an 8 foot ceiling height.

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