HVAC Sound proofing

Discussion in 'Home Theater Projects' started by Austin R, Jan 16, 2005.

  1. Austin R

    Austin R Auditioning

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    Hello all,
    I am in the planning stages as to how advanced I want to sound proof my Supply/Return cooling and heating. I am finishing my entire basement myself with the except the HVAC and drywall. I had a HVAC contractor out and he said the best way would be to install a separate cooling system alltogether (around 11k). I asked him if there were any other non-extreme methods, but he said that he didn't really think so. Can anyone provide any specific information as to what "muffling" techniques they might have used? Also, where is the best place to install the supply and/or return? I will have a 2 inch & 12 inch rise subfloor.

    any input would be appreciated!

    Thanks,
    Austin
     
  2. Wayne A. Pflughaupt

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    Wayne
    Austin,

    I’m not sure why you feel the need to soundproof your AC system.

    AC ducts these days are flexible hoses with interior insulation that turn and bend at least several times from starting point to destination. When you consider that sound waves travel in straight lines, it should be clear that any mid- and upper frequencies traveling through them will be sufficiently (if not thoroughly) blocked long before they make it to the main unit and back out to other rooms.

    The most problematic situation in soundproofing is blocking transference of bass frequencies to other rooms. As such your soundproofing dollars would be better spent on more traditional soundproofing methods – staggered stud or room-in-a-room construction, doubling sheetrock or other density-improving methods, sealing the room airtight, etc.

    Regards,
    Wayne A. Pflughaupt
     
  3. Austin R

    Austin R Auditioning

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    Hi Wayne,
    thanks for your comments. My house only has flexible ducting for the fresh air intake and equalizer. The supply and return lines are all aluminum. (This may be a minnesota thing?!) I checked with all my neighbors, new construction & different builder, and they are the same way.

    My biggest concern is that my girlfriend will be able to hear the hear while sleeping through the return vent as they are all common.

    thanks,
    Austin
     
  4. SteveLeach

    SteveLeach Stunt Coordinator

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    From what I've read here and on other boards, what you need is to use the flexible ducting for both the supply and the return. Use a minimum of 2, 90 degree bends to eliminate direct path transferance of sound into your existing heating/cooling system. And you want to over size the ducts to reduce the air flow noise.
    Hope this helps
     
  5. Bri~A

    Bri~A Agent

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    You do not need to use flexible ductork to reduce the sound transmitted. As long as there are a few 90 deg. bends in the ductwork b/w outlet locations, that will help reduce the sound transfer issue.

    SteveLeach is right that you should oversize the ducts a bit to avoid air noise. Calculate your duct sizes with a pressure drop of about 0.08 to avoid noise and make sure your supply and return outlets are sized properly for the amount of air. Watch the NC values (should be less than 20) for your supply diffusers with the amount of air you will be pushing thorough them (size ther necks accordingly).

    If your theater is close to your AHU and you are concerned about fan noise being transfered through the ductwork and into the theater, you can always use accoustical lining for the first 20 feet or so of ductwork on the unit discharge. This may be getting a bit extreme though.

    Hope this helps a bit.
     

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