vibration in ceiling

can someone help with this problem? i have a problem with vibration in my (spare) bedroom ceiling that i cannot stop -- finding the source is easy -- the furnace and a/c evaporator is directly overhead. As far as i can tell, there's nothing wrong with either unit -- i suspect that when the home was originally built (about 5 years ago) that somebody did a lousy job of hanging the sheetrock and/or isolating the upstairs unit.
i have put in about 15 sheet rock screws but the vibration continues -- it's wierd, if you just barely touch the ceiling the vibration will stop but give it about 30 seconds and it'll start back...
any suggestions? should i continue with the sheetrock screws (my ceiling looks like a gunfight broke out! :)...anyone ever had this problem...
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wrote:

Whatis the frequency of the vibration? The 60 Hz house current hum? The furnace motor vibes? A squeal? Rattles? from the water pipes?
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hi papa -- it's not 60 Hz current home; it only occurs when the air conditioning is cycling on -- otherwise no sound...

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The problem is related to the HVAC unit. It is a typical problem with attic mounted units. The cure is doing something to the unit, not adding screws to the drywall.
It should be installed on isolation pads with vibrasorber connections to any and all duct work.
An additional solution would be to suspend the unit by all- thread with vibration damping couplings, keeping it completely off the ceiling framing.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

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Dan -- thanks for this. I was wondering about this. There appears to be absolutely no isolation in the unit now so any thing i do along those lines should help. One thing with using the drywall screws is that I'm just creating a more solid connection to the vibration source and that could make things worse not better...i think you're right that isolation / dampening may be the way to go...

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That's right. In dealing with vibration isolation, the key things are to reduce the stiffness of the connection, increase the mass of the thing vibrating or increase the damping. Increasing the damping is actually harder than it sounds. Getting the equipment on a soft mount is the best first step. Increasing the mass of the ceiling is also possible - adding sand as someone suggested. However, that isn't going to affect the damping as another poster assumed.
If you can't change the mounting of the equipment, you could hang the ceiling from resilient channel supports.
Mike
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the isolation pads appear to be really cheap but it doesn't seem like a very good do-it-yourself job -- it's such a frustrating problem! i've seen pads on the internet for this purpose at about $1.50 for an 8 inch square pad...if i'm not mistaken...
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Come to think of it the air exchanger units, in each of my daughter's houses, which run continuously 24/7 are suspended by vibration damping straps. Also the pipes which connect it are soft and flexible. In one case it is immediately below a bedroom and the other immediately next to a bedroom. Never heard any complaints about noise or vibration. Granted that an AC unit has a more powerful motor, but idea the same.
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Terry -- i imagine that the kind of dampening you're talking about is the best -- perfect isolation!

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Can you sprinkle some sand on top of the ceiling?
Nick
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nick -- what would that do. would it show the vibration pattern or something or are you saying it'll work like magic fairy dust and make the problem go away...:))

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wrote:

Do you mean lay a bag of clean dry sand up there, on top of the ceiling sheetrock, to dampen the vibration. Cheap and might be worth a try? Should certainly change the 'resonance frequency' of the ceiling which sounds like it is acting as sound board? After all if the vibration is that severe anything/everything in the house that could vibrate at an annoying audible frequency could be shaking and rattling. Enough to keep one awake nights? If the sandbag doesn't work as a sound dampener, use it as weight ballast for winter driving! Winter time we have four bags of sand/gravel plus iron weights in back of our pickup truck. Also at a pinch put some sand under the driving wheels to get traction on ice!
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i may give that a shot -- i already moved some heavy stuff next to the unit but it didn't stop the problem...
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It might simulate your "barely touching the ceiling..."

Maybe a pound or two, for damping. Not a whole 50 pound bag.
Nick
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thanks for the suggestion Nick.

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You are welcome. I wouldn't have suggested it if you hadn't mentioned that barely touching the ceiling killed the vibration. I've simulated fingers in electronic design. If you want to dampen, don't use frictionless sand :-)
Nick
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Tell your wife to shut off her vibrator when she is not using it.... Be sure to use the word "PLEASE".
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