I am happy to have found this venue. It appears to be a black hole, in celestial terms, of knowledge and good advice.

I need some advice in solving an unforeseen noise transmission problem in an all concrete and steel stud pool building.

To set the stage, all the mechanical equipment, including heat pumps (4), geothermal loop circulators and pool related equipment  such as a Dryotron and associated distribution underfloor ducting , are located in a 5'-5"  crawl space under the  front apron of the pool building and within the building envelope.

All copper pipes, steel conduits and circulating pumps are either hard fastened to the concrete ceiling or suspended from the ceiling via ready rod.

There are no sound transmission attenuation measures taken to mitigate the direct transmission of sound from the various noise generators to the concrete and beyond.

Additionally this is complicated further by two 10" vertical metal ventilation ducts which connect the crawl space , traveling in a chase up the wall to deliver dry air to a skylight overtop of the pool.

Further, in the roughly 15'X15' space housing all the mechanical equipment there are six  perimeter floor penetrations housing  4"X 14" vertical metal ducts bringing ventilation  to the windows in the upper pool wall areas.

The stud cavities at pool level are filled with closed cell PolyUFoam.

We are at the, pre-drywall stage,  with a plan to finish with 5/8" drywall and stucco finish with a tile floor.

The noise transmission from the mechanical room directly through the concrete floor and the floor penetrating ductwork is quite loud and unpleasant.

I would be grateful for any suggestions, both obvious and obscure, including materials, which could be employed to mitigate this situation.


Castor

I have given some thought to this problem over the week end after reading this forum for many hours.

There is a lot of smart people on here, so thank you for your indirect contributions to my dilemma.

Isolating all the mechanical equipment that is directly bolted to the concrete ceiling is pretty straight forward.

Dealing with the air duct penetrations through the concrete floor up to the window sills is a bit more difficult.

I have thought of furring out the walls above the mechanical room and insulating the ducts directly, approximately 1-1/2" space, and then applying some Quiet Rock drywall on the surface.

The ducts could be insulated in the mechanical room up to the ceiling and perhaps from above, on the inside as well.

My question is, what would be the best material to use for sound insulation in the furred out space and over all the duct work both in the mechanical room and above it?

The walls above the mechanical room are concrete and the ducts are encased in 2 lb closed cell poly foam insulation between the steel studs.

Any thoughts?

Open cell foam is much better at sound attenuation.

http://www.stcratings.com/assemblies.html

Posted By Castor on 21 Nov 2011 01:36 PM
I have given some thought to this problem over the week end after reading this forum for many hours.

There is a lot of smart people on here, so thank you for your indirect contributions to my dilemma.

Isolating all the mechanical equipment that is directly bolted to the concrete ceiling is pretty straight forward.

Dealing with the air duct penetrations through the concrete floor up to the window sills is a bit more difficult.

I have thought of furring out the walls above the mechanical room and insulating the ducts directly, approximately 1-1/2" space, and then applying some Quiet Rock drywall on the surface.

The ducts could be insulated in the mechanical room up to the ceiling and perhaps from above, on the inside as well.

My question is, what would be the best material to use for sound insulation in the furred out space and over all the duct work both in the mechanical room and above it?

The walls above the mechanical room are concrete and the ducts are encased in 2 lb closed cell poly foam insulation between the steel studs.

Any thoughts?

Open cell will give you a much better sound control.

This site has several good bits of information on wall assemblies and their performance.   http://www.stcratings.com/

Quiet rock is nice stuff but I think you can get 95% of what you need from conventional drywall assemblies or even more from a stacked wall effect.

You may want to contact an engineer . Sound Transmission problems can be very difficult to resolve . Mechanical equipment operates with different frequencies. One method or product may only deaden a certain frequency. Your vertical shafts are acting like amplifiers.Ductwork should have offsets and can be constructed to absorb fan noise either from blower or the velocity of air moving within the ductwork.Noise attenuators may be necessary. Shaft enclosures should be constructed using sound board and multiple layers of drywall.

Posted By acwizard on 24 Nov 2011 01:20 PM
You may want to contact an engineer . Sound Transmission problems can be very difficult to resolve . Mechanical equipment operates with different frequencies. One method or product may only deaden a certain frequency. Your vertical shafts are acting like amplifiers.Ductwork should have offsets and can be constructed to absorb fan noise either from blower or the velocity of air moving within the ductwork.Noise attenuators may be necessary. Shaft enclosures should be constructed using sound board and multiple layers of drywall.

Thanks for your reply.

This is not my area of expertise unfortunately, but I have recognized that there is a problem worth addressing.
All the pumps have been removed from the ceiling mounts and any direct supporting rods have now been mechanically isolated.
You can actually feel the difference.

The biggest issue was always the floor penetrations and the ductwork in the mechanical room.

My insulating contractor has suggested spraying all the ductwork in the mech room with small fiber fiberglass/glue and doing the same thing on the ducts above the ceiling in the pool area itself.

I will ask an acoustic engineer to visit once all the equipment is fired up, to address the myriad of frequencies at play, then spray or use whatever may be needed to address that.

I agree with you that sound board and drywall will likely play a significant role here, Just wish someone had foreseen this issue a little earlier in the build, nonetheless, sometimes solving a problem on the fly can be rewarding intellectually, were it not so painful in the wallet area.

In my opinion , Spraying the ductwork in such a manner is probably a waste of time and money.Duct liner is best for absorbing noise. Uunfortunately in your application it would not be wise to do so.The the moisture content present because of the pool enviroment may cause other problems such as mold. Would love to see some pictures.

I would look at a bed liner material like Lizard skin for consideration as well.

Be cautious about using certain types of materials. They must meet flame and smoke requirements as per NFPA.