I'm going to do a DIY absorber panel, but have some questions...

Discussion in 'Home Theater Projects' started by Jones_Rush, Sep 13, 2003.

  1. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    202
    Likes Received:
    0
    I want to go according to the plans here:
    http://pat.home.mchsi.com/SAP.html

    This is according to Jon M. Risch's plans, right ?.

    If I will go with Miraflex instead of ordinary fiberglass (health issues). Should I need to expect weird consequences for this choice ?.

    According to this page:
    http://www.owenscorning.com/around/i...s/miraflex.asp

    The thickness of Miraflex is 8 3/4". But the question is, will Miraflex absorb as good as regular Fiberglass ?. If they absorb more or less the same, then how come people are still using regular fiber glass ?, is there a really big price difference between the two ?.

    One last question, about the absorption coefficient of this DIY panel. Has anyone run any measures to see that the absorption coefficient is more or less constant throughout the entire frequency band ?. As long as it's 0.9/0.8 and above (from the starting frequency) then it should be good. But if it has variations, like from 1.2 at 900hz, to 0.5 at 4000hz, then it can't be good.

    Whith commercial pannels I get a frequency table which always shows me a more or less constant absorption coefficient, so I believe this is pretty important in order to get good subjective results...
     
  2. ThomasW

    ThomasW Cinematographer

    Joined:
    Nov 6, 1999
    Messages:
    2,282
    Likes Received:
    0
    Rush

     
  3. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    202
    Likes Received:
    0
     
  4. ThomasW

    ThomasW Cinematographer

    Joined:
    Nov 6, 1999
    Messages:
    2,282
    Likes Received:
    0
    To do this the right way start by getting a copy of ETF 5.0

    Then follow the instructions on their Demo Room Page

    Then decide if, where, and how, you should use any sound absorbing panels. And what type of panels are needed.

    BTW if you actually need real bass traps look HERE and HERE for info. If you want to make bass traps with fiberglass they'll need to be 12-24" thick.

    My DIY panels use 2"X4"s with 6" thick fiberglass batts.

    You can use anything you like for the back of the panels.
     
  5. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    202
    Likes Received:
    0
    Thanks for the answers Thomas.

     
  6. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    202
    Likes Received:
    0
    edit.
     
  7. Pat

    Pat Agent

    Joined:
    Jun 30, 1997
    Messages:
    47
    Likes Received:
    0
    Jones, glad my step by step process is helpful [​IMG]
     
  8. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    202
    Likes Received:
    0
    Yes Pat, very! :).
    Btw, is there anything about the construction you would have done differently, if you were to build it again today ?. I saw you didn't use a layer of poly batting behind the fiber glass (only in front), is there a reason why not ?.
     
  9. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    202
    Likes Received:
    0
    Here are some waterfall images of the left speaker, at the listening spot. This is with digital room correction (which can't do a good job for the higher frequencies reverberation anyway) and with acoustic treatments (heavy blankets and pillows at first/second reflection points, and at the closet behind my head).

    1ms:
    http://www.avsforum.com/avs-vb/attac...chmentid=12505

    3ms:
    http://www.avsforum.com/avs-vb/attac...chmentid=12506

    5ms
    http://www.avsforum.com/avs-vb/attac...chmentid=12510

    10ms
    http://www.avsforum.com/avs-vb/attac...chmentid=12509

    The situation is very similar with the other speaker too.

    As you can see, up to about 2ms, the work of the absorbers can be seen (the speakers are 1 feet away from the side wall next to them, no option to change that). After that, things become really bad, really fast. Some say that in order to get good sound you need at least 5-10 ms of no reverb after the main spike. There is no possible way to achieve this, as you can see, without going with a much more comprehensive absorbing scheme, which might need to include an entire absorbing "ring" across the room. Treating just points simply won't work.
     
  10. ThomasW

    ThomasW Cinematographer

    Joined:
    Nov 6, 1999
    Messages:
    2,282
    Likes Received:
    0
     
  11. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    202
    Likes Received:
    0
     
  12. RichardHOS

    RichardHOS Second Unit

    Joined:
    Mar 11, 2003
    Messages:
    454
    Likes Received:
    0
    Jones,

     
  13. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    202
    Likes Received:
    0
    RichardHOS,

    Your post was all that needed in order to push me to the dark side, completely :). Goodbye 2ch stereo, Hello multichannel! (and huge, HUGE amounts of Miraflex.[​IMG] )
     
  14. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    202
    Likes Received:
    0
    Richard,
    I'm wondering, do you think that DPL-II or Circle Surround II in multichannel with a deaden room, will be at least as good as a typical LEDE room with plain 2ch stereo ?. I have access to both these algorithms through the PC (I'm running my sound system through the PC).
     
  15. RichardHOS

    RichardHOS Second Unit

    Joined:
    Mar 11, 2003
    Messages:
    454
    Likes Received:
    0
    I don't have any direct experience with CS or CSII. I have heard a great L7/dead room implementation, and no stereo setup I've ever heard could compare. I'm not sure how CSII and L7 stack up, other than the anecdotal knowledge that L7 is highly respected.

    I will say that a good LEDE implementation can sound fantastic, that much is sure. A good multichannel implementation can also sound fantastic... of that I am also sure. The important piece of the puzzle is that LEDE isn't so great for multichannel playback, which makes it incompatible with movie and multichannel audio uses to a greater or lesser degree (depending, of course, on how live the LE is and how dead the DE is).

    So... with plain 2ch stereo I think it would likely be a tossup with between a good LEDE room and a dead/multichannel setup using CSII, DPLIIx, etc. L7 and Trifield would likely be better, all other things being equal (source, speakers, etc.).
     
  16. Pat

    Pat Agent

    Joined:
    Jun 30, 1997
    Messages:
    47
    Likes Received:
    0
    Jones,
    The fiberglass batts have a paper backing on them, so putting any dacron behind wouldn't do much good.

    I basically followed Thomas' directions except that I used burlap instead of muslin.
     
  17. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    202
    Likes Received:
    0
    Richard,
    How important is the center channel when DSP'ing a stereo signal, to a multichannel one ?. Is it good practice to go with only two speakers at the front, and four at the back ?.

    For music alone, I never find the center channel too useful. For movies though, it's an entirly different story.
     
  18. RichardHOS

    RichardHOS Second Unit

    Joined:
    Mar 11, 2003
    Messages:
    454
    Likes Received:
    0
    That depends on the quality of the DSP, and the quality of your center channel. Typical centers with limited extension and poor horizontal dispersion aren't exactly to best choice for music.

    However, with a good center (i.e., same as L/R ideally) and good DSP (trifield, L7), there are some very good reasons for not removing it from the system. Reduced comb filtering will result in an increased sweet spot size and image stability. Just remember... when you hear a trumpet solo on stage, it comes from a point source. We (audiophiles) have for years had this concept that stereo (two-channel) is the "proper" way to recreate the front soundstage, and that a center channel messed that up. Well, that's just a result of having grown up (most of us) with two speakers. Go listen to a real symphony and you'll immediately see where a center channel comes into play.

    Personally, I hope we eventually wind up with something like 5 horizontal discrete channels up front (and maybe a couple more for height, plus whatever rear concoction they come up with).

    That being said, not all centers are created equally, and (from my admittedly limited time with L7/trifield) not all DSP's are created equal either.
     
  19. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    202
    Likes Received:
    0
    In my case, the major problem is the center location. I simply can't put it at the same height level of the mains, or bring the mains lower.

    Somehow, and I really don't know how to explain this, for movies the imaging really lacks without the center speaker, everything sound MUCH better with the center (the room is practically energized with the center, and completely drown out of life, without it). But, with music, the inaccuracy of the center's height, really comes into play. I get much better imaging without it (even with pre recorded 5.1 music).

    Anyway, according to what you say, it doesn't seem like I'm going to lose too much by going with a phantom setup, if I'm satisfied with the image stability and wideness of my current stereo configuration.
     
  20. Jones_Rush

    Jones_Rush Stunt Coordinator

    Joined:
    Jan 19, 2001
    Messages:
    202
    Likes Received:
    0
    What options do I have, if I don't want to go with fiberglass at all (not even Miraflex) ?. Isn't there any safe (health wise) alternative which absorbs good enough, even for more money ?.
     

Share This Page