Author Topic: Rooftop AC Unit noise Q  (Read 1279 times)

homehouse

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Rooftop AC Unit noise Q
« on: May 07, 2019, 06:10:05 PM »
Hi there
Great site. I am learning so much about just about everything.

I live in an older condo on the top floor (floor 3), lucky me. Pretty good view. On my roof/ceiling right above my bedroom, are the six heat pump units for the units. Vibration from one or more of the units is causing vibration humming sounds. Before I reapproach the hoa, I have been trying to see if I can mitigate the problem by using isolation pads. Hoping it is not pipe vibrations.
Couple of questions.
(1) points of support - how many? The units are pretty small (300-400 lbs), so I see recommended four 2x2 pads (one in each corner). If four is good, does it make any sense to put more points of contact? i.e.: six? Add one more on each side or one in the center of the pan?
(2) thickness / how many layers? - if one layer is good, does it make sense to put a second layer (make a pad sandwich) just to be safe? I am looking at individual pad thickness of approx 5/8-3/4" for approx total double thickness of 1-1/2".
(3) D rating? - I see different durameter ratings available. All the way from d20 - d80.

Thanks in advance.

homehouse

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Re: Rooftop AC Unit noise Q
« Reply #1 on: May 07, 2019, 07:32:00 PM »
I would also ask whether a larger pad (4x4) helps or hurts.
Thanks

Randy S

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Re: Rooftop AC Unit noise Q
« Reply #2 on: May 08, 2019, 03:25:00 PM »
1) less contact points is better decoupling and more vibration reduction.
2) each pad is 7/8" thick, people do double up but reduction of vibration does not double, slight improvement but not expensive to do.
3) our durometer on those are 65.

I do have a company that is using our ssp foam mat 2" thick and claims to out do all the vib pads. just more expensive.

Randy S.
760-752-3030
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

homehouse

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Re: Rooftop AC Unit noise Q
« Reply #3 on: May 09, 2019, 05:47:40 AM »
Thanks very much for the answers. Helps. And on the question of size is it better to use larger (4x4) or smaller (2x2)? It sounds like it might be better to use smaller if the they are speced to handle the weight.

Randy S

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Re: Rooftop AC Unit noise Q
« Reply #4 on: May 09, 2019, 03:14:06 PM »
yes smaller, the pads can hold 50lbs per sq.in. so a 2x2 can hold 200lbs.

Randy S.
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

homehouse

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Re: Rooftop AC Unit noise Q
« Reply #5 on: May 19, 2019, 06:09:04 AM »
I’ve doing more research and acquired some neophrene isolator pads (2x2 .375”) with duroneter rating of around 45. I doubled them up and they definitely helped decreasing the vibrations by 50%. I did more research and planning at the recommendation of a contractor to insert and glue a steel plate between the pads to see if that further reduce the levels. The pads are not solid but have a kind of of a kind of x pattern cut outs through them. Fortunately, I can access the roof easily and slip in and remove and test different pads to see what works. The bad thing is that the problems units are not under my control so I have to wait until they kick in and be in my unit to see the pads are effective. Will report.