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  1. #1
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    which supply register is "quiet-est"?

    by type:

    Perforated

    bar type

    adjustable ("flaps" which can be closed)


    Im doing a small refurb here where the meeting room will be used for training/testing.......they want it very quiet. I realize all moving air makes noise but overall, which type grille is going to give me the least amount of noise?


    thanks all.

  2. #2
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    I would have to say Perforated, the building I work in is full of them and also linier slot diffusers for perimiter.

  3. #3
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    May 2007
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    http://metalaire.com/documents/Info/PCD/7000_Info.pdf
    This may help; the spl is listed as nc value which you can use to compare which one is going to suit your requirements.
    Just go to the manufacturer's site of choice.
    Last edited by adrianf; 04-25-2008 at 03:40 PM.

  4. #4
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    Velocity is a larger problem concerning noise than diffuser type. I agree perfs are somewhat quieter but don't mix as well and tend to stratify in heating. Enlarging the duct size say from an 8" to a 10" the last 5' or so will swap area for velocity and decrease noise. Also have the damper away from the diffusion at least that much.
    I should have played the g'tar on the MTV. MK

  5. #5
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    Slot diffusers with a lined plenum box are pretty quiet.
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  6. #6
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    Quote Originally Posted by hvacker View Post
    Velocity is a larger problem concerning noise than diffuser type. I agree perfs are somewhat quieter but don't mix as well and tend to stratify in heating. Enlarging the duct size say from an 8" to a 10" the last 5' or so will swap area for velocity and decrease noise. Also have the damper away from the diffusion at least that much.
    I agree - make sure you put in a balancing damper a ways upstream of the diffuser. By being able to close down the balancing damper just a bit will help a bunch with noise. If they are really concerned put in sound attenuators upstream of the ductwork serving the conference room.
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  7. #7
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    we use these alot

    FILL OUT YOUR PROFILE!!

  8. #8
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    Jun 2005
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    Any diffuser, if given too much air will be noisy.
    Application dictates type.
    Matching the manufacturer's specs to the volume/inlet static/throw required to the diffuser's design requirements will mostly assure an acceptable noise level.
    Lately, I've seen 12" diameter 2x2's with 450 CFM design flows....that will not be silent. Putting 2-2x2's in it's place would substantially quiet them down.
    So number of diffusers play a role also.
    jogas

  9. #9
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    Dec 2007
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    thanks for all the input gents. Should be enough info to achieve desired sound level.

  10. #10
    Join Date
    Apr 2007
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    Los Angeles
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    FYI, we just built a recording studio in Santa Monica and noise was critical.
    We used Mitusbishi "city" units that were specifically designed for low velocity which helped a lot, but all the registers (return and supply) were two slot linears with oversized plenums lined with 2 inch duct liner.

  11. #11
    Join Date
    Apr 2008
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    Orange County, CA
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    Quote Originally Posted by hvacker View Post
    Velocity is a larger problem concerning noise than diffuser type. I agree perfs are somewhat quieter but don't mix as well and tend to stratify in heating. Enlarging the duct size say from an 8" to a 10" the last 5' or so will swap area for velocity and decrease noise. Also have the damper away from the diffusion at least that much.
    I agree that too high of velocity will make the diffuser louder, but oversizing it too much will increase the tendency of the air to stratify and not mix well. I would call a local rep for Titus or some other manf. They know their products and are very helpful even if you're not planning on using their product (but don't tell them that).

    Another thing to keep in mind is that sound data for diffusers are from testing air coming in from perfectly straight duct. You want to try to stick to this by putting a few feet of straight duct into the diffuser if possible. Running flex along the ceiling and elbowing into the diffuser in the last foot isn't going to make it quiet.

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