How to quiet an HVAC System

Discussion in 'Home Theater Projects' started by Darren{Moo}, Sep 7, 2004.

  1. Darren{Moo}

    Darren{Moo} Extra

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    Does anyone have any suggestions on how to quiet the air "whoosh" of a central hvac system. It really seems quite loud in theater when the system activates. You don't hear the running of the motor, only the rush of air through the duct. I have heard of some type of silencer by a company called Kinetics, but my web searches revealed only industrial type units. Any help, discussion, etc. is appreciated.
     
  2. Demetrius

    Demetrius Agent

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    Darren,
    If you can increase the size of the vents it would reduce the noise as it passes through it. If there is a way to increase the size of the ducting it would also reduce the "noise" but that is probably not possible. The basics are bigger ducting and vents - reduce any bends in the duct or use sweeping turns if possible. Other than that anything else would probably reduce the cooling efficiency of your system.
     
  3. Wayne A. Pflughaupt

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    I recently took mine down to run them through the dishwasher (needed cleaning) and I immediately noticed that it was a lot quieter with it out. If you have no reason to close the vent it would probably help to gut the closing flaps out.

    Regards,
    Wayne A. Pflughaupt
     
  4. Jay Mitchosky

    Jay Mitchosky Producer

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    A couple of other solutions...

    Use ducts that are lined with sound absorbing material, and run such that there are several 90 degree turns. The rushing air bounces into the corners is progressively damped in sound.

    Install large air diffusers at the outputs. Vent noise is largely a function of turbulent air and the diffuser smooths this out. As suggested above larger vents help as well as the same volume of air can move with less pressure and speed.

    Construct and install silencing plenums along the duct path. Kind of hard to explain but it's essentially a large'ish box placed in the middle of the air flow. The intake and output from the box are offset and the cavity is lined with sound absorbing material. I saw the design of this detailed in an AV magazine once and the intent again is to break the speed and turbulence of the air without restricting flow. It also blocks the direct path for noise to travel.

    Problem here is that any or all of these solutions may be difficult or impossible to implement depending on the location of your theater and how much access you have to the ducts.
     
  5. Jay Mitchosky

    Jay Mitchosky Producer

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  6. Leo Kerr

    Leo Kerr Screenwriter

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    The worst offender (in my experience) is the actual diffuser itself. In our living room, we pulled the ducts, and to keep the air from just blasting down on the people sitting under the two boxes, I did some custom building.

    Take foamcore, and build boxes that extend down from the box in the ceiling. Two sides only, in my case; your milage may vary. The bottom of the box was angled away from the corner made by the two sides, sending the air out into the room, almost silently - especially when compared to the prior diffuser (that didn't work very well, anyway.)

    I suppose, if you've got a center mounted diffuser, you can do two opposite sides, and then '^' the 'bottom' of the box.

    On the other hand, I'm still trying to figure out how to quiet a 'casement' window-shaker that's in the home theater. Right now, it's just off when we're watching... but when you're doing Return of the King, it gets kinda warm...

    Leo Kerr
     
  7. Darren{Moo}

    Darren{Moo} Extra

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    Thanks for the info guys. Fortunately I have access to the ducts feeding my theater room so I'll be able to give each of the ideas here a try. I'll report back after I make some modifications.
     

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