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Discussion Starter · #1 ·
I've used MLV extensively before but there are two things I'm wondering about before I line the rest of my new car with it.

The general recommendation here is to decouple. However, I've come across a number of sources that say decoupling can actually make low frequency performance significantly WORSE. For example:


1) So if a vehicle is decently deadened otherwise -- ie high frequencies not really an issue -- I'm wondering if NOT decoupling the MLV would actually yield better performance in a car and help with the troublesome low freqs. Thoughts?

2) Has anyone tried using a heat gun on MLV to get it to form better around contours? Or any other tricks for making it easier to contour to a convoluted floor pan without making the carpet stay weird afterwards?
 

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The analogy seems suspect to me... I've read the Green Glue website and I'm not clear that we are talking apples and apples. The drywall actually becomes a piston generating sound if not properly controlled, as I understand it...
 

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yeah, drywall vs steel metal floorboard isn't a good comparable to justify the same results the graph is displaying... I also think that keeping sound "out of the vehicle" is the primary purpose of MLV... at least in my application it would be...
It's kinda scary how that graph is lowest between 63-100 Hz, though (the audible freq of a sub) :surprised:
 

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It's true - Green Glue has some very out there "documentation" on their site. As VP Electricity said, a lot of apples to oranges comparisons. Seems like a reasonable product, but some of their stuff makes you wonder.

All of that said, decoupling is overplayed in this application. It makes great sense in theory, but in practice, it doesn't seem to do much. One of the major online sellers of MLV describes all of the important reasons you need a decoupling foam layer, but when you compare the STCs for the two products, there is no difference :surprised:

In my testing over well damped steel, 1/4" of foam makes no difference until you hit 1kHz when it starts absorbing. Below that and the two fluctuate a few dBs up and down. You do run into problems over very resonant steel, but you shouldn't have that anyway. I'm going to have to revisit this. I brought up the same point a while ago and allowed myself to be convinced that I was wrong.

The concept makes sense for a number of reasons, but most of them would require a MUCH thicker decoupler than is practical for us. The 1/4 wavelength rule seems to apply. Even so,most noise has a high frequency component so attenuating it doesn't hurt.

Heating MLV doesn't really do the trick. You can get it to follow a slightly tighter radius, but you really have to heat the hell out of it and you can't really get it to follow a complex contour.
 

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There's no "out there" documentation. All very standardized for the construction industry. All following standard ASTM guidelines and data from independent certified acoustic labs. What you guys are doing isn't construction, so things are a little different.

Decoupling: Not applicable for damping car body parts. The reason is that along with the physical disconnection of material layers, there is the understanding that a significant sealed air cavity will be imparted. This is a 2-3" space requirement. Again, not applicable for what you are looking to achieve.

Green Glue is also not applicable for what you're doing. There are two types of damping systems. The first is Extensional Damping. Painting on a thick layer of a rubbery material that will reduce the (steel) material's ability to conduct a vibration. This again is a surface "painting." Glueing MLV to steel would be another example of Extensional Damping.

The second type of damping is Constrained Layer Damping. This is the use of a different damping material (Green Glue, etc) and reequires the Green Glue to be constrained between two layers of material. Two pieces of drywall, etc. Again, not what you are looking to achieve.
 

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Discussion Starter · #6 ·
Thanks for sharing your thoughts everyone. I just wanted to get some discussion on this going since we all want quiet cars -- of course -- but there doesn't seem to be much information on this stuff dealing with our application.

Ted -- I'm not sure that I understand. Are you saying that decoupling is useless in a car, or are you saying that the graph I posted doesn't apply to cars? Also, you know, the most popular "sound deadening" products for cars are actually vibration dampers (butyl with aluminum foil constraining layer). Your products seem to be very well regarded by the home theatre guys and I've been wondering for a long time if it might be a viable alternative for us car guys instead of the butyl stuff. Would it be suitable for this and if so how would you compare it to the butyl/foil products?
 

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Thanks for sharing your thoughts everyone. I just wanted to get some discussion on this going since we all want quiet cars -- of course -- but there doesn't seem to be much information on this stuff dealing with our application.

Ted -- I'm not sure that I understand. Are you saying that decoupling is useless in a car, or are you saying that the graph I posted doesn't apply to cars? Also, you know, the most popular "sound deadening" products for cars are actually vibration dampers (butyl with aluminum foil constraining layer). Your products seem to be very well regarded by the home theatre guys and I've been wondering for a long time if it might be a viable alternative for us car guys instead of the butyl stuff. Would it be suitable for this and if so how would you compare it to the butyl/foil products?
That depends on your definition of 'sound' in 'sound deadener' - it's sometimes used in the context of vibration dampener and doesn't completely cover it. It deadens vibrations and the 'sound' the resonating panel makes, but doesn't block or reflect the 'sound' of road noise or music very well at all. In home theater, there's more leighway to build a massive wall of layers. In cars, you're limited to about 1/2" in a lot of spots that you want to block sound. I picked up a bunch of Damplifier and Luxury Liner Pro for sound barrier. Luxury Liner Pro has a 3/8" closed-cell foam layer to de-couple and mass-loaded vinyl for blocking and reflecting sound. These are demonstrating to be very effective in quieting your car. There are a lot of threads here with very useful information.
 

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2) Has anyone tried using a heat gun on MLV to get it to form better around contours? Or any other tricks for making it easier to contour to a convoluted floor pan without making the carpet stay weird afterwards?
Glue or velcro it down.
 

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Also, you know, the most popular "sound deadening" products for cars are actually vibration dampers (butyl with aluminum foil constraining layer).

I've been wondering for a long time if it might be a viable alternative for us car guys instead of the butyl stuff. Would it be suitable for this and if so how would you compare it to the butyl/foil products?
The MLV and butyl, in my estimation is the way to go. Like what SDS.com has
 

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Just to throw something out there, seems to me that most of the noise in a car that you are trying to block out is not in the sub 100hz range. I understand that sub 100hz noise is being made by the speakers, but if that gets out does that really matter. Butyl should stop the panels from excessive vibration, and the MLV decoupled will stop the road noise from getting in.

If I am wrong someone please tell me as this is the theory I am working with when I start my sound deadening project.
 

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That's not my website, however the data is correct. Concepts are correct.
Let me be clear. I've never used Green Glue because there doesn't seem to be much application in a car because of the requirement that at least one of the sandwiching materials be air permeable. My impressions of the product have been favorable. It sounds like you have some relationship to the product, but now that isn't clear. That looks like Green Glue's Web site to me.

Te presentation I linked to has been discussed here before. Each sub panel may present correct data and concepts, but taken together the viewer is led to make certain conclusions about the efficacy of MLV vs. Green Glue. In the first place, since each represents a completely different approach to different problems, they aren't mutually exclusive. In the second, the MLV is used in sub-optimal arrangements. That's why I'm questioning it. To me it looks like putting up data about a person's need for water vs. air and stipulating that the water can only be used directly from the sea It just seems like an unnecessary comparison.
 

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Just to throw something out there, seems to me that most of the noise in a car that you are trying to block out is not in the sub 100hz range. I understand that sub 100hz noise is being made by the speakers, but if that gets out does that really matter. Butyl should stop the panels from excessive vibration, and the MLV decoupled will stop the road noise from getting in.

If I am wrong someone please tell me as this is the theory I am working with when I start my sound deadening project.
Just to be clear, butyl alone isn't going to deal the resonance - it has to be constrained, but your idea is correct. The point of this thread is to determine the role decoupling plays in a barrier's performance in our application. The assumption that it is critical has come from construction data where spaces are greater, existing barriers are more massive and the goal is to prevent voices from passing through walls. The notion of using a foam decoupling layers seems to fall in the same category as using multiple layers of CLD at 100% coverage - accepted wisdom that is wrong.

In my testing, I've found very similar results sandwiching steel/foam/MLV and steel/MLV/foam which suggests to me that the foam is just acting as a high frequency absorber - a good thing, but not a decoupler. The results get a little unclear around the resonant frequency of the steel panel. My tests are pretty crude and more study needs to be done. Nonetheless, vibration damper/barrier is the way to go - we're just investigating what 1/4" of foam between them accomplishes.

I'm close to being convinced that the ideal application for the inner door skin is vibration damper/MLV/foam. The MLV replaces the vapor barrier and adds mass to the steel which already has a good airspace between it and the outer skin. The foam contributes to high frequency attenuation AND reduces rattles and buzzing of the door card that it would be in contact with.
 

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I'm close to being convinced that the ideal application for the inner door skin is vibration damper/MLV/foam.

Interesting suggestion here, used like this the MLV would not be decoupled, however you are suggesting that the decoupling is not doing that much in a car anyway.

I will offer a different idea on how to use the MLV in a door, I would suggest that it would be best used on the outer skin. When used on the inner skin it would need to have holes in for mounting tabs, speakers, door arms and such. We know that MLV works best when the seams are sealed, on the outer door skin it would be easier to accomplish a layer of MLV that does not have holes then it would be on inner skin. Just a thought.
 

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there doesn't seem to be much application in a car
There isn't. That's been my point all along. For many reasons including porous layers as you mentioned, heat, optimal damping at frequencies not relevent to your needs, etc.

That looks like Green Glue's Web site to me.
I think it is. That's not my website.

the MLV is used in sub-optimal arrangements.
That's not so. For construction applications MLV has been shown to perform nearly identically regardless of how it is inserted in the wall. Mass is mass. But this isn't a construction forum, and you aren't building walls.

MLV and similar panels seem to be the perfect product for your application. I came here to dispell any thoughts of Green Glue being used to damp panel resonance.
 

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That's not so. For construction applications MLV has been shown to perform nearly identically regardless of how it is inserted in the wall. Mass is mass. But this isn't a construction forum, and you aren't building walls.
But inserting a layer of 1 lb/ft² MLV between two layers of drywall doesn't add much to the total mass/area of the package - that's what I mean by sub-optimal. Green Glue in the same configuration is performing a completely different function rendering the comparison silly, IMO.
 

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Interesting suggestion here, used like this the MLV would not be decoupled, however you are suggesting that the decoupling is not doing that much in a car anyway.

I will offer a different idea on how to use the MLV in a door, I would suggest that it would be best used on the outer skin. When used on the inner skin it would need to have holes in for mounting tabs, speakers, door arms and such. We know that MLV works best when the seams are sealed, on the outer door skin it would be easier to accomplish a layer of MLV that does not have holes then it would be on inner skin. Just a thought.
That's the theoretically ideal configuration for blocking sound, but unless you have a Saturn and can take the door panels off, installing a contiguous barrier on the exterior skin, working through the access holes gets old really fast - some vehicles more than others.

I'm just suggesting that you can get most of the barrier benefits while vapor sealing the door, isolating the front and back waves from door mounted speakers and a few other things, while making the job much easier. Unless somebody actually tests this, it's even possible to theorize that the barrier on the inner skin will be more effective since there is less opportunity for noise coming in through the sides of the door to bypass the barrier.
 
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