# Foam or Fiberglass for soundproofing?



## Ted White

Hi all,

This is a common question, so perhaps some might find this interesting.

When we’re looking to soundproof a partition (wall or ceiling) we’d like to introduce Absorption in the otherwise hollow wall or ceiling cavities. Foam is a common consideration, however not appropriate for what we want. For damping the resonance in the air cavity, we prefer medium density fiberglass, cellulose, mineral fiber or polyester. All of these are open and “airy” enough to adequately interact with the sound waves.

Foams are not adequately open. “Open cell” foam is certainly better than closed cell foam, but not as high performance as something like humble fiberglass. Additionally, foam can couple the two sides of a wall or floor, allowing much better conduction of the vibration from surface to surface.

Foams are superior from a thermal perspective, but not a sound isolation perspective.

This might surprise some here, but when using insulation IN a wall or ceiling, it doesn't get any better than standard thermal insulation in a low / medium density, especially to control low frequencies. This could be fiberglass or medium density mineral fiber. http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/ir/ir693/ir693.pdf This extensive lab report conducted by the Canadian government has the data. 

Seems counter-intuitive, and there are many companies that capitalize on the intuitive aspect of insulation as a solution to sound control. Also perhaps counter-intuitive, we never want to compress / compact (stuff) the insulation. The greater the compaction, the greater the conduction of vibration from one side of the partition to the other.

Further, there are only 4 soundproofing elements that we can bring to bear:

Decoupling
Absorption (insulation)
Mass
Damping

Of these 4, absorption brings the least to the table. We certainly want to install insulation where we are able, but know that the other 3 elements provide more demonstrable improvement.


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## ejbragg

Ahh, practical sense, at last! Great info, Ted. Keep it coming!


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## Ted White

Thanks. I find as time goes on, there are more and more nonesense products coming on the market that have no data, no lab tests and a predatory reliance on trying to tap into a customer's intuition. Sort of angers me.


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## PepAX7

Ted White said:


> Thanks. I find as time goes on, there are more and more nonesense products coming on the market that have no data, no lab tests and a predatory reliance on trying to tap into a customer's intuition. Sort of angers me.


I'm with you, Ted. We find this in the electronics world, in all facets, and it just plain bugs me how these companies get away with "bilking" people whose lack of knowledge puts them in a "fact finding" mission. Of course, with the internet, anyone can start a blog and post whatever nonsense they like.:dumbcrazy:

That's what makes the Shack work! Posting some of this science/research here, will help in that mission.

I haven't studied the Canadian report but plan on it. I've also been researching an insulation company named ROXUL, who publish their STC's on their website. Their Roxul AFB lists an STC of [email protected] for 4" material. That's pretty impressive to me.

I want to build some traps modeled after F. Alton Everest's designs and want to test out different materials for "tuning" the trap.

A builder/musician friend of mine say's he uses Roxul between adjoining townhouse walls and he swears by it for noise attenuation. It's all in the measuring, isn't it?:bigsmile:

Thanks for your expertise!

Pep


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## Darnstrat

What's been your experience using HDPE sheeting as a sound barrier coupled with rock wool?


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## Ted White

Hi Pep. Its all about the measuring is right. Having said that, studies in that referenced report show that fiberglass is slightly better in the low frequencies than mineral fiber.

Darnstrat: I haven't tested HDPE however its all about the mass. Whatever is heavy to build your leaves from. HDPE, MDF, Drywall.. All are heavy. It's a matter of cost and ease.


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## bassman17

Fantastic thread and initial post! Foam in the middle of a wall..... oy! what will be next?

The only thing I would like to add is my experience with insulating between leaves is that it also dampens the tympanic resonance of the drywall itself and thus providing a bit more isolation at the coincidence dip of the panel.

Fiberglass is cheaper than rockwool and you can get a contractor to install it for less than you would pay for the material alone due to their bulk purchasing power.

Now fiberglass for acoustic control within a space is a different matter.....

-ashley


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## WilliamSmith

soundproofing foam is the best option.


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