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Thread: Diffusers in early reflection zone?

  1. #1
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    Diffusers in early reflection zone?

    I've considered to add some diffusers on my absorbent drop ceiling and some RPG Bad panels (or somthing similar) on sidewalls closest to the listening position. The reason is because I would like to get some more liveliness and it would also be good to cover the frame of the drop ceiling which are causing some reflections.

    If I do this, it will be in the area of early arrival sound, within 10 ms. And many are saying that it's better to use absorbents for early reflections and rather add more dffusion for later reflections, typically after 20 ms.

    Another thing I'm uncertain about is if using diffusers in a narrow place like this (on drop ceiling and sidewalls), will cause unwanted specular reflections.

    I've attached some pictures and the lines on the drop ceiling are the places I've thought using diffusers. The pictures are somewhat outdated. I've removed the diffuser on the frontwall, using less absorption on sidewalls and started to make some changes on the slanting ceiling now, but they still give a good impression.

    I use diffusion only on the backwall today. The absorbents you see behind the speakers and on the slanting ceiling behind speakers are covered with a reflective membrane of mids and highs. An exception is the superchunks in the cornes that absorp all the way up.

    Would be great with some input concerning adding diffusion. Will using diffusion in those areas cause specular reflections? Am I better off adding diffusion on the frontwall in front of basstraps?
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    Last edited by Bjorn; 05-01-2011 at 03:08 AM. Reason: spelling

  2. #2
    WBF Founding Member Nicholas Bedworth's Avatar
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    Bjorn... how does this arrangement of panels sound? Do you have any impulse response tests that you could post? I'd be very interested in Art's take on this as well.
    Nicholas Bedworth, CTO
    DigitalDirect Development Corporation
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  3. #3
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    I am interested in Art's reply as well. My experience has been that diffusion can be as effective as absorption but results in quite different sound since more energy is "retained" in the room (versus being aborbed in the panel). Diffusors generally cost more, and obtaining broadband diffusion is often more difficult than broadband absorption. Whether you absorb the energy, or break it up so it is no longer correlated to the primary signal, it should improve the image. Again IME, diffusors provide a "bigger" sound while absorbers provide a "tighter" image. Which you prefer is always a matter of some debate... The latter (absorbers) should be more true to the source material, assuming a fairly dry mastering studio (not always a good assumption), but most seem to prefer the former (diffusors) for the sound's "presence".

    All imho - Don
    Don Herman
    "After silence, that which best expresses the inexpressible, is music" - Aldous Huxley

  4. #4
    WBF Founding Member Nicholas Bedworth's Avatar
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    Don,

    Fascinating response and thanks. Let me run this by the diffusor panel manufacturer, who in so many words has told me the same thing, and also the acoustical engineer who's working with us.

    Nick
    Nicholas Bedworth, CTO
    DigitalDirect Development Corporation
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    A really, really big bird in the hand is worth...

  5. #5
    Member Sponsor microstrip's Avatar
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    Disclaimer - I am not an acoustic expert, but I did a lot of experiments with absorbers and diffusers in my room. My experiments also point towards Don conclusions, but I would like to add there are many different types of absorbers, and most of the classical DIY recipes have severe dips in the absorption spectrum and produce unpleasant results due to their non uniform or irregular absorption.

    My final preference went mainly to diffusion with some corner absorption. But I look for a spacious sound.

  6. #6
    WBF Founding Member Nicholas Bedworth's Avatar
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    See, if you were an expert, you'd set up a room that measured perfectly, and sounded poorly!

    The notion of diffusors with corner absorption sounds good to me, as I prefer a spacious sound as well.
    Nicholas Bedworth, CTO
    DigitalDirect Development Corporation
    www.digitaldirect.com

    A really, really big bird in the hand is worth...

  7. #7
    Addicted to Best! naturephoto1's Avatar
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    When I discussed my room with Bryan of GIK Acoustics we discussed using a combination of absorption and diffusion. I started by installing absorbing Bass Traps and Acoustic Panels:



    The above photo is a portion of the front wall of the room. Additional Bass traps were placed in the rear of the room with Bass traps placed above the subwoofers.

    Bryan and I discussed what would be the next step after the first round of Acoustic Room Treatments. We decided to use diffusers on the side walls and for the ceiling for the first reflection points (we hope we caught them correctly). When the diffusers were installed I also installed additional Bass Traps (Tri-Traps) above the seating and added fiber fill to the diffusers that were installed on the ceiling. As a result, the diffusers on the ceiling act as both diffusers and absorbers at the same time. The third round of acoustic room treatments were additional Acoustic Panel absorbers that may be at/near the 2nd reflection point (we were still noticing an echo around the seating). The next 2 photos show the diffusers and acoustic panels on the side walls from round 2 and 3 of the installation:





    The last photo shows the diffusers on the ceiling that also has fiber fill in wells of the diffusers to also act as absorbers:



    I am pleased with the results thus far.

    Rich
    Last edited by naturephoto1; 05-16-2011 at 01:02 PM.
    Richard A. Nelridge

    http://www.nelridge.com

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    I should note that my current room is pretty dead, for various reasons. One of them being its relatively small size. In a good-sized room, my preference is a mix, with absorption in the corners and first reflection points and diffusors further back along the side walls and ceiling, plus the middle of the front wall and back wall. I find diffusors at first reflection points tend to muck up (that's a technical term ) the image to me and so I prefer absorbers there, but I like having some diffusion around to provide a more "spacious" sound.

    I believe that puts me in line with Rich's room, somewhat a comfort considering how well that looks and (I assume) sounds. - Don
    Don Herman
    "After silence, that which best expresses the inexpressible, is music" - Aldous Huxley

  9. #9
    WBF Founding Member audioguy's Avatar
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    Rich: what brand r your equipment racks? Very nice (as is your room)

  10. #10

    Hmm... interesting.

    I would make two points:

    People tend to use "diffusor" and mean only one type of diffusor - the quadratic-residue type. RPG has done a good job marketing QRDs as 'the' diffusor, based on their research, but I encourage everyone to also think about "coherent" (more accurately, "phase coherent") diffusors, which have been in use for hundreds of years.

    I like phase-coherent diffusors because our species has a few million years' experience with naturally-occurring phase-coherent diffusion, and only a few years of never-before-heard-in-nature non-coherent diffusion. Quadratic-residue diffusion is non-coherent. Coherent diffusors, like polycylindrical and cylindrical types, are much easier to use and more affordable as well (disclaimer: I develop products for Acoustic Geometry, which makes phase-coherent cylindrical diffusors).

    OK, three points: vertically-oriented phase-coherent cylindrical diffusion used at the first-reflection point, along with diffusors placed "next to" the listening position (on the walls, also vertically oriented, 90-degrees on either side) makes a listening room sound much more open and natural (a few horizontally-oriented cylindrical diffusors in between helps a lot, too). Try it. I really dislike absorbers in the first-reflection point - they deaden the whole room, and they are never truly broadband.

    My $0.02. I expect others will differ.

    Nice thread!

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