Report: is closed cell foam the right material to decouple mass loaded vinyl?

[Justin Zazzi]

This was originally posted on DIYMA forum on December 16, 2018:



Back in the summer of 2017 I wanted to test a common rule of thumb: mass loaded vinyl should always be decoupled from nearby surfaces, and closed cell foam is the right material to do it.

Many of you kindly donated materials for this experiment and I am very, very thankful for it. I am thrilled to finally finish and post the results. This took a very long time to write because I did not have a solid method to interpret the results until just recently when we covered the transmissibility ratio in an acoustics class I'm taking. I apologize for the delay, but I hope the wait is worthwhile.

the report is at my dropbox here --> MLV decoupling report v1.3

[spwath]

Very interesting report, I am going into my senior year majoring in mechanical engineering with an acoustics concentration so this stuff is very interesting to me.

I wonder though, how much does the size of the mlv squares used affect results? It seems like scaling up, a lot more factors could come into play.

[Justin Zazzi]

Cool! Mechanical engineering is my degree as well and it has been very useful. I'm happy to answer any questions you have about the acoustics industry or how to pursue a career in sound. Actually, a great place to start would be ALMA's annual event called AISE. It is normally a few hundred bucks and you'd have to travel to Las Vegas and rent a hotel and everything, but this year it is free to anyone who registers and it'll be online.

As for the size of the MLV squares, it should scale nicely since the stiffness of the decoupling layer depends on the surface area of the material, and so does the mass of the vinyl. The common surface area should cancel out the change in mass and the change in stiffness of the spring. I'm pretty sure the scaled-down samples I tested were a good representation. Do you see something different?

[Pb82 Ronin]

Can we have a cliff's notes of the results? You know, for those of us that don't read engineering jargon well.

[Justin Zazzi]

Can we have a cliff's notes of the results? You know, for those of us that don't read engineering jargon well.

Have you tried the conclusion on the last page?
Sorry it feels full of jargon. I tried to make it less jargony but it's hard.
Is there something specific I can clarify?

[spwath]

Cool! Mechanical engineering is my degree as well and it has been very useful. I'm happy to answer any questions you have about the acoustics industry or how to pursue a career in sound. Actually, a great place to start would be ALMA's annual event called AISE. It is normally a few hundred bucks and you'd have to travel to Las Vegas and rent a hotel and everything, but this year it is free to anyone who registers and it'll be online.

As for the size of the MLV squares, it should scale nicely since the stiffness of the decoupling layer depends on the surface area of the material, and so does the mass of the vinyl. The common surface area should cancel out the change in mass and the change in stiffness of the spring. I'm pretty sure the scaled-down samples I tested were a good representation. Do you see something different?

Not too sure if it would make a difference, but I was just thinking, as right now the 1.5" square is somewhat rigid, but a bigger sheet of vinyl would have a lot more flex to it.

Also, while these results do show a lot at what is the most effective, it doesn't really show how big of a change it makes. For that the experiment would need to be done by mounting the system on a car doo/metal piece and measure the transmition loss. That actually sounds pretty interesting to do, I will have to see if I can do that at all next year, as my college has an anechoic chamber and reverberation room, with a removable panel between them to specifically measure transmition loss.

[rton20s]

Have you tried the conclusion on the last page?
Sorry it feels full of jargon. I tried to make it less jargony but it's hard.
Is there something specific I can clarify?

I think you did a great job of keeping the "jargon" down. I thought the document was well written and straight forward enough for a laymen like myself to understand. And before I saw your reply, I was going to point Ronin to your conclusion, as well.

Not too sure if it would make a difference, but I was just thinking, as right now the 1.5" square is somewhat rigid, but a bigger sheet of vinyl would have a lot more flex to it.

Also, while these results do show a lot at what is the most effective, it doesn't really show how big of a change it makes. For that the experiment would need to be done by mounting the system on a car doo/metal piece and measure the transmition loss. That actually sounds pretty interesting to do, I will have to see if I can do that at all next year, as my college has an anechoic chamber and reverberation room, with a removable panel between them to specifically measure transmition loss.

You might be interested in taking a look at the test rig that Chris Purdue (aka TooStubborn2Fail) is currently building. It is designed to test CLD, but I believe he plans to expand the testing beyond that to materials like MLV and lead for transmission loss.

[preston]

I think the conclusion is there is no point to "decoupling" MLV except to sell stick-on CCF. Just install the MLV and skip the whole decoupling mantra.

That being said I do like to have some stick-on CCF around, its great for isolating wire bundles or trim panels that touch but one shouldn't expect it to "absorb" sound waves or reduce vibration in MLV installs.

[Justin Zazzi]

I think the conclusion is there is no point to "decoupling" MLV except to sell stick-on CCF. Just install the MLV and skip the whole decoupling mantra.

That being said I do like to have some stick-on CCF around, its great for isolating wire bundles or trim panels that touch but one shouldn't expect it to "absorb" sound waves or reduce vibration in MLV installs.

Essentially, yes that is what the report says.

I should have highlighted some of the benefits though like having a stick-on material like you describe, or the benefit of having something between the MLV and the sheet metal to reduce the chances of rattles/buzzing. There can certainly be benefits to having intermediate materials, but not for the sake of "decoupling" like is commonly claimed.

[opekone]

Very great work! I love the idea of mounting to the driver to create a simple and repeatable process where the harmonic resonance of the mounting surface is continuously variable.

I'm interested in the effect of the overall size of the MLV or the decoupling layer since they both gain their spring and dampening curves from the interaction of neighboring material. Replicating results with a much smaller piece, say, 5mm x 5mm, would go a long way to demonstrating the efficacy of this methodology.

In vivo, as it were, the speaker's output is significantly dampened and modified by the air and when it hits an object (like your inner door skin) it excites that object at it's natural harmonic resonance. While mounting directly to the speaker does provide a great view into the variability across difference resonant frequencies, I wonder if it's an accurate recreation of our use case. Here the only interaction we are seeing is that of the decoupler + MLV interacting with the harmonic resonance of the material. We don't assess it's ability to mitigate the airborne sound nor do we assess the combination of effects. This is particularly curious to me because in our application we typically use CLD rather than decoupled MLV to deal with harmonic resonance.

Is Jazzy even still here?

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