# MLV: inner vs. outer door panel??



## pharmkook (Feb 23, 2010)

Obviously, applying the MLV between door card and inner panel is easier, but does applying the MLV to the outer door panel improve its function enough to justify the difficult application?


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## dbiegel (Oct 15, 2006)

Not worth it. In fact, it may actually be counterproductive, for three reasons:

1) Road noise - Due to the window, drain holes, and air flow, you can never have a great seal inside the door cavity. Sound will come in through the leaky areas regardless of how impressive you get the outer skin. Furthermore, it'll prevent some of that road noise from being reflected away by the inner skin, by "trapping it" and reflecting it back toward the car instead of letting it exit (see #3 below).

2) Door mounted speaker(s) SQ - This will just cause more sound to be reflected back into the car from the speaker(s). In fact, it might be best to actually have a very poorly insulated outer skin, and then make the inner skin extremely well insulated. This will act as the ultimate infinite baffle around the speaker, with sound allowed to escape out of the car through the weak skin behind the speaker.

3) Sound tends to get "trapped" when there are two parallel (or (almost parallel) surfaces that have very high blocking ability. This can cause all kinds of standing waves and related issues that can hinder the performance of door mounted speakers and cause road noise to resonate at certain frequencies.

Instead of using MLV here, the ideal would be to cover the outer skin in just enough CLD to keep it from resonating, and then cover that with as thick (moisture-safe) foam as you can fit.


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## sriskie (Feb 6, 2010)

Forgive my ignorance...but what is MLV and CLD?


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## ItalynStylion (May 3, 2008)

Mass Loaded Vinyl
Constrained Layer Dampener


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## nar93da (Dec 11, 2008)

I've been thinking of putting it in both place's since G35's are so easy to apply to the outer skin but I guess I won't now!


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## ItalynStylion (May 3, 2008)

It would also weigh a ton per door with two layers. I can't even imagine.


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## negativegain (Oct 6, 2009)

dbiegel said:


> Not worth it. In fact, it may actually be counterproductive, for three reasons:
> 
> 1) Road noise - Due to the window, drain holes, and air flow, you can never have a great seal inside the door cavity. Sound will come in through the leaky areas regardless of how impressive you get the outer skin. Furthermore, it'll prevent some of that road noise from being reflected away by the inner skin, by "trapping it" and reflecting it back toward the car instead of letting it exit (see #3 below).
> 
> ...


so everyone we see posting pics of their install that deadens both inner and outer door skins are doing it wrong? i have seen numerous cars done this way.
and more to my point, i have and audi a6 with no inner door skin to speak of.
just the outer with a diagonal brace and then the interior door panel that hooks onto said brace.
my mids mount to the interior panel so should i not deaden the outer door skin?
btw, i will be using ss damplifier.


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## dbiegel (Oct 15, 2006)

Deadening an outer door skin is a good thing, but using MLV on it might not be. 

I don't know much about your Audi but the basic acoustic principles are the same... a speaker produces sound both forward and backward. When the two waves combine, cancellation and other negative effects result. The ideal is to separate the two waves as much as possible. So you want a solid barrier like MLV between the front and the back wave. On most cars, this means the inner door skin.

An optimal speaker enclosure is made of a solid, non-resonant material and minimizes internal reflections. The outer door skin is really close to the back of the speaker making reflections a bigger problem. You want to deaden the outer skin so it's solid and non-resonant, but you don't want to create even more internal reflections by using something like MLV on it.


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## negativegain (Oct 6, 2009)

ah, ok.

i had mlv and products like damplifier confused.
thanks for clearing that up for me.
there is already quite a lot of dampening material from the factory, but i'm gonna add a lil more once it warms up.


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## Rudeboy (Oct 16, 2005)

dbiegel said:


> Not worth it. In fact, it may actually be counterproductive, for three reasons:
> 
> 1) Road noise - Due to the window, drain holes, and air flow, you can never have a great seal inside the door cavity. Sound will come in through the leaky areas regardless of how impressive you get the outer skin. Furthermore, it'll prevent some of that road noise from being reflected away by the inner skin, by "trapping it" and reflecting it back toward the car instead of letting it exit (see #3 below).
> 
> ...


I agree with this almost completely. There are several advantages to installing a barrier on the inner skin. Better rejection of noise and acoustically reinforcing the plane the speaker is mounted to are the most important. Hanging a barrier on the outer skin is reasonable if your primary concern is making door mounted speakers harder to hear from outside the car or if your vehicle doesn't meet the two requirements for inner skin mounting:

there must be sufficient space inside the trim panel to accommodate at least 1/8” material thickness, preferably, 1/4” or 3/8”
the trim panel must cover the entire interior surface of the door when closed
Most modern vehicles meet these requirements.

Isolating the front and back of the speaker is absolutely critical - I've installed barriers on the inner skin of vehicles with stock speakers in the doors and the difference in performance is pretty amazing. I'll disagree a little about how much you can do to mitigate what happens inside the door with the sound coming from the back of the speaker. I doubt adding a barrier to the outer skin would make an audible difference. I'm also very skeptical about attempts to attenuate the back wave with absorption. 

Water flows through doors. That means that if you put foam on the outer skin, it has to be closed cell. Closed cell foam is a very poor absorber for the same reason it won't hold moisture. Available space is another problem. Even if you have room for a 1/2" layer of foam, it will only be effective at frequencies >= 3.4 kHz, 1" >= 1.7 kHz. That's just a small slice at the very top of what most door mounted speakers will be producing. Better to seal it off and let it do what it wants on the other side of the baffle.


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## pharmkook (Feb 23, 2010)

Seems that inner door panel (between door card and inner panel of door) makes most sense....

Probably MUCH easier from an install standpoint too... I can use a few sheet metal screws to attach the MLV on inner, but would be stuck with glue or velcro only on outer panel.

Thanks for helping!!!


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## pshoffman (Jan 17, 2009)

Reviving an old thread. 

I agree it is really hard to put a MLV layer between the door card and in the inside door skin. Too many interference points with the door card.

I am planning to put a MLV layer on the "outside" of the inside door skin. The outside doesn't have the interference points. I will have to use velcro to hold it in place as well as CCF on the inside of the MLV, facing the interior of the car.

Anyone done this and have any concerns or insights?

Thanks


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## Truthunter (Jun 15, 2015)

pshoffman said:


> Reviving an old thread.
> 
> I agree it is really hard to put a MLV layer between the door card and in the inside door skin. Too many interference points with the door card.
> 
> ...


Not sure about your car... but in mine the window motor/mechanism is mounted to the surface you are talking about. Besides it already being difficult to see this surface, It would be just a real pita to work around the window mechanism and make it so it does not interfere with it.


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## Rudeboy (Oct 16, 2005)

You have to remove the glass and regulator to install MLV on the outer door skin. You'll also want to put the CCF between the MLV and door skin, not the other way around. 

There are enough advantages to putting these materials on the inner skin, behind the trim panel, that's it's worth the effort. It's not possible on a few vehicles, but is on most, with varying degrees of difficulty. Mostly just takes patience.


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## pshoffman (Jan 17, 2009)

My car is a Porsche 997 911. The inner door skin has a bolt-in panel that takes up most of the door area and seals the door fairly well. The window motor is attached to this panel. 

It would be fairly easy to install the MLV panel to the outside of the inside skin with a cutout for the motor. 

I could then bolt in the panel to the inner skin and then attach the motor to the panel. I could reach in behind the panel through the woofer hole to postion the motor for bolting.


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## pshoffman (Jan 17, 2009)

So the question is, is it as good to have the MLV layer on the "outside of the inside skin" versus the "inside of the inside skin". I am not thinking about putting it on the outside skin of the door.


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## Rudeboy (Oct 16, 2005)

pshoffman said:


> So the question is, is it as good to have the MLV layer on the "outside of the inside skin" versus the "inside of the inside skin". I am not thinking about putting it on the outside skin of the door.


That will work perfectly - shouldn't make any difference in performance at all. Good way to go. I've done that on old trucks with no trim panels on the doors and removable panels. Only modification to normal practice I might consider is running a strip of waterproof, vinyl compatible tape over the top edge. That would force water over the top of the MLV instead of behind it, eliminating any possibility of it getting stuck between the sheet metal and waterproof CCF and MLV. Don't think that's a highly likely possibility, but still ..


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