# Understanding door sound deadening theory



## Rossi (Dec 21, 2016)

Hi All,

I am just trying to understand the importance of the different treatments and effects, please share your inputs and correct me if my understanding is wrong.

*
- Sealing off holes in inner door skin*
Main purpose is to block or prevent backwave from entering into cabin to avoid muddy sound caused by cancellation of the main front wave.

*
- Dampening outer skin*
To reduce traffic noise
To reduce resonance caused by backwave? Or is the resonance caused by the speaker driver movement energy? Whats the main cause of resonance?

*
- Placing a CLD dampener directly behind driver*
Whats the purpose? Is it to absorb backwave? 
But CLD don't absorb wave right? It is just to dampen and reduce resonance, the backwave is never absorbed?
Does this placement of CLD in the outer skin directly behind speaker driver helps? And in what way it helps sound quality?


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## tRidiot (Jun 29, 2006)

Foam directly behind the speaker to absorb backwave.

CLD on the inside of outer (and inner) doorskin to reduce resonance/vibration effect.

Seal holes with sandwich of sheet metal/butyl to add stiffness and reduce vibration and resonance, also to reduce potential backwave propagation back into the doorcard. Sheet metal screws to attach to door. This will reduce road noise significantly. 

Full coverage layer of viscoelastic mat/closed cell foam between the doorcard and inner door skin to further block backwaves and reduce vibration between doorcard and inner door skin. I attached mine to the inner door skin with heavy velcro. An additional layer of lead sheeting would further reduce road noise significantly, but would make it much heavier. Attachment might be an issue due to the weight.

This will yield doors that shut with the sound of a vault door - or a tomb.


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## Notloudenuf (Sep 14, 2008)

See if this is helpful
http://www.diymobileaudio.com/forum...7-simple-cheap-effective-door-treatments.html


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## dgage (Oct 1, 2013)

Don't go cheap. I bought a roll of a cheap copy of Dynamat and I've been dealing with small leaks out the bottom of my doors when it gets hot out. Then again, I put that stuff on in layers, not the CLD tiles they recommend now.

This is a popular place with DIYMA members though there are others.
https://www.sounddeadenershowdown.com


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## Justin Zazzi (May 28, 2012)

tRidiot's post is good, but I would like to answer some of your questions a little more directly.



Rossi said:


> *
> - Dampening outer skin*
> To reduce traffic noise
> To reduce resonance caused by backwave? Or is the resonance caused by the speaker driver movement energy? Whats the main cause of resonance?


Damping of any material (inner skin sheet metal, outer skin, door card, etc) is to reduce the physical vibrations of the material in both magnitude (how far the panels move back and forth) and also in time (how long they resonate for). The added effect of a CLD treatment is the resonant frequency lowers too, which usually means the resonance is buried in the road noise or is less audible than a higher pitched ringing. Adding CLD tiles will have a tiny effect on reducing noise from passing through the material such as exterior road noise entering the cabin, and an air-tight dense layer of anything such as mass loaded vinyl is a better tool for that purpose.



Rossi said:


> *
> - Placing a CLD dampener directly behind driver*
> Whats the purpose? Is it to absorb backwave?
> But CLD don't absorb wave right? It is just to dampen and reduce resonance, the backwave is never absorbed?
> Does this placement of CLD in the outer skin directly behind speaker driver helps? And in what way it helps sound quality?


CLD directly behind the woofer is not a bad idea since directly behind the woofer is where the sound waves will first encounter the sheet metal, and cause it to start moving. If you have a limited amount of damping material then applying it near this area might give you the most bang for the buck (assuming the area behind the woofer is broad, flat, and prone to resonance).

You're right that a CLD does not absorb any sound. You would need open cell foam or something like fiberglass to do that, and the thickness of the absorbing material makes all the difference in which frequencies can be absorbed. The thicker the material, the lower the frequency it can attenuate. The the average car door can't fit more than a few inches worth of absorbing material, so the low frequency absorption is limited, although absorbing higher frequencies is not a bad thing either.


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## sq2k1 (Oct 31, 2015)

Subbed for interest....


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## tRidiot (Jun 29, 2006)

Jazzi said:


> tRidiot's post is good, but I would like to answer some of your questions a little more directly.
> 
> 
> 
> ...


You're right... MLV and foam is the sandwich I meant for between the sheet metal and door card. My bad. I was post call and half in a bottle. lol


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## Marky (Nov 15, 2011)

I myself just did this to my 2006 Ford F250, at least in my own way.

I installed two layers of GT Mat 110mil to the outer door skin in strips. I covered the entire outer door. Then I put 1" CCF over that also the entire door area. I used aluminum tape on all of the strips to seal it completely. 
Then I put two layers of GT Mat on the inner door and closed up the large openings with aluminum sheetmetal and also covered that with GT Mat. I put a much lighter foam rubber over that so the door panels could compress it enough to latch into place.

The only real openings that I have is where the door panel clips into the door itself.
I thought about sealing those off too but did not go through the effort. Made a huge difference in stopping any road noise coming through the doors. Also did the entire floor of the truck along with firewall and roof area under the head liner.

I have not finished my stereo install on this truck quite yet. But my prior truck I did the same thing and the stereo sounded beautiful. Very nice midrange sound and the best part was at any volume all I heard was the stereo.

Its a lot of work to do but I assure you will love it once its done. There are a lot of options available and Dyna-Mat is not the only that works. McMaster Carr has a lot of sound proofing foams available for doing this. I used their CCF for under the door panels and they sell a aluminum faced foam that I installed under my cab as well.
My truck is a diesel and I cannot hear the engine at all going down the road. Its well worth the effort and the door speakers will sound much better too. A sheet metal enclosure is a lousy setup for any speaker regardless if its a cheapie or the best speakers made.
Good Luck its worth it fellas.......


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## Marky (Nov 15, 2011)

I myself just did this to my 2006 Ford F250, at least in my own way.

I installed two layers of GT Mat 110mil to the outer door skin in strips. I covered the entire outer door. Then I put 1" CCF over that also the entire door area. I used aluminum tape on all of the strips to seal it completely. 
Then I put two layers of GT Mat on the inner door and closed up the large openings with aluminum sheetmetal and also covered that with GT Mat. I put a much lighter foam rubber over that so the door panels could compress it enough to latch into place.

The only real openings that I have is where the door panel clips into the door itself.
I thought about sealing those off too but did not go through the effort. Made a huge difference in stopping any road noise coming through the doors. Also did the entire floor of the truck along with firewall and roof area under the head liner.

I have not finished my stereo install on this truck quite yet. But my prior truck I did the same thing and the stereo sounded beautiful. Very nice midrange sound and the best part was at any volume all I heard was the stereo.

Its a lot of work to do but I assure you will love it once its done. There are a lot of options available and Dyna-Mat is not the only that works. McMaster Carr has a lot of sound proofing foams available for doing this. I used their CCF for under the door panels and they sell a aluminum faced foam that I installed under my cab as well.
My truck is a diesel and I cannot hear the engine at all going down the road. Its well worth the effort and the door speakers will sound much better too. A sheet metal enclosure is a lousy setup for any speaker regardless if its a cheapie or the best speakers made.
Good Luck its worth it fellas.......


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## Lanson (Jan 9, 2007)

Where's Don? His website does a great job covering the SCIENCE, not just the theory.

GT Mat? Fail. At least out here (hot desert temps). I have a huge leftover stack of various models of their product sitting on my shelves.

I'll use Don's stuff or Knu Kolossus.


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## tRidiot (Jun 29, 2006)

I don't know about GT, but can highly recommend Don's stuff from SDS. It is just flat awesome.


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## TOOSTUBBORN2FAIL (Jan 31, 2011)

GTMat 50mil, 80mil, and 110mil are asphalt products, and all fail heat testing. They do slightly better than peel n seal in heat testing, but they will still fail over time.


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## Rocketjones (Oct 23, 2008)

Because you're in Asia, check out melamine foam. If you can layer it. It is useful from like 400hz -2k-4k hz sound dampening. Layering it has a greater effect. Plus it is dirt cheap.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140017768.pdf
www.acousticalsurfaces.com/foam_stop/mel_comp.htm


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## Marky (Nov 15, 2011)

There's no way my GT Mat is ever coming off, I put it in the sun before installing and then used a commercial heat gun to soften it and fuse it into the steel. Its fused like a tire patch volcanizes to rubber.
I am well aware that GT Mat is a asphalt rubber combination but it works. And for its cost I put 300 lbs of it into my truck with fabulous results. My truck reminded me of my childhood riding the school bus to school. Now I shut the doors and its like a Cadillac with a solid thump and the best part is I no longer hear road noise or the engine.

I used Dyna-mat on my old truck and this truck is quieter yet. But I will admit that I used more material then I did in my old truck. As well as more multiple types of materials in my current truck. I put four layers of 110 mil on my doors, two on outer skin and two on the inside door skin. Then put 1" CCF on top of that and the CCF were different weights as well. Used denser CCF on the inside of the doors "outside door skin".
Both are foam rubber materials but I also used a 1/4"firm foam material on the backside of the door panels. I forget exactly what it was called now.
Pretty amazing how I can tap and knock on my doors now and you cant hear it inside the truck. It worked well that I will say. 
McMaster Carr does sell soundproofing material and is where I purchased some of the material that I used.
If you are looking for the biggest bang for your buck check out the sites posted above. There are several outfits that sell quality soundproofing for inside your doors.

Enough rambling good luck with your project.


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## Rossi (Dec 21, 2016)

Rocketjones said:


> Because you're in Asia, check out melamine foam. If you can layer it. It is useful from like 400hz -2k-4k hz sound dampening. Layering it has a greater effect. Plus it is dirt cheap.
> https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140017768.pdf
> Melamine Acoustic Composite Foam For Soundproofing



Thanks for the suggestion, will try to source if there's anywhere selling this material.
This is to be stuffed into the door card right?


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## Rossi (Dec 21, 2016)

One thing I would like to understand, what is the main cause of the door resonance when playing music?

The main culprit is the speaker cone movements? 
Backwave energy is not so strong to cause so much resonance on the door panel, I am assuming.

Once I just went outside my car and closed the door with the music playing. I placed my hand on the outer door skin, I was so surprised on the amount of resonance, even though the music I am playing is not really that loud.


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## Rossi (Dec 21, 2016)

Notloudenuf said:


> See if this is helpful
> http://www.diymobileaudio.com/forum...7-simple-cheap-effective-door-treatments.html


This link is real useful, a full door treatment method.


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## Rocketjones (Oct 23, 2008)

Rossi said:


> Thanks for the suggestion, will try to source if there's anywhere selling this material.
> This is to be stuffed into the door card right?


The material is the same as the "magic eraser" sponges sold across the world. I found them awful cheap on amazon. It was like $8 for 100 pieces - 3.55" X 2.4" X 1.2" or ( 90mm X 60mm X 30mm), which is plenty to put on the outer door skin of my vehicle, directly behind the speaker on top of several layers of MLV. If your speaker is not sealed from the inside of the door card, I would apply at least one layer surrounding the speaker if you can fit it. It has been my experience, isolating the speaker from the inside of the door card will give better cabin response. YMMV.


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## BMW Alpina (Dec 5, 2012)

dgage said:


> Don't go cheap. I bought a roll of a cheap copy of Dynamat and I've been dealing with small leaks out the bottom of my doors when it gets hot out. Then again, I put that stuff on in layers, not the CLD tiles they recommend now.
> 
> This is a popular place with DIYMA members though there are others.
> https://www.sounddeadenershowdown.com





fourthmeal said:


> Where's Don? His website does a great job covering the SCIENCE, not just the theory.
> 
> GT Mat? Fail. At least out here (hot desert temps). I have a huge leftover stack of various models of their product sitting on my shelves.
> 
> I'll use Don's stuff or Knu Kolossus.


I have GTMat on my door and it leak the asphalt all the time when it's summer... plus it was a bit smelly...

I wish I buy Dynamat...

I also install GT Mat on the firewall behind/under the plastic wiper cowl,
so it got exposed to engine heat... and it peel off after few months...

My guess is they do work in colder climate states... but not in CA...

Strange thing is... I put them under the roof right behind headliner too, and so far,
knock on wood, they don't leak and don't peel...
perhaps because the roof surface was very clean when the GT Mat applied... and then no moisture goes in there much ...


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## Lanson (Jan 9, 2007)

BMW Alpina said:


> I have GTMat on my door and it leak the asphalt all the time when it's summer... plus it was a bit smelly...
> 
> I wish I buy Dynamat...
> 
> ...



Yeah I bought a large stack of GM Mat Quadro which is double-layer Butyl and foam/foil, and their Butyl can't-remember-the-name (edit: think it was Onyx??) but it was a thinner material, and both lacked enough stick to stay on metal. I had to peel and redo with Knu Kolossus which is sticky enough to be considered a nuisance should you "miss" (so don't miss!), and the remaining Quadro and whatever is just sitting. It DOES have good properties other than sticking so sometimes I sandwich the stuff between things that don't need to stick (like a sub box and an amp rack put together), to act as a damping layer. But in a car with deadening tiles, STICK is a really important property so in that measure, no GT Mat for me.

As I just realized after a few posts, our OP here is in Asia. I do believe there are some Euro and Asian deadening brands like Noico that may be worth looking at. 


But as far as the Science of it, follow www.sounddeadenershowdown.com and read his research topics on it. He's also easy to email and talk with, and he's very passionate about the subject. That's Don's site there.


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## Marky (Nov 15, 2011)

BMW Alpina said:


> I have GTMat on my door and it leak the asphalt all the time when it's summer... plus it was a bit smelly...
> 
> I wish I buy Dynamat...
> 
> ...


That's interesting because I didn't smell any odor at all when I installed it into my truck. As far as sheet metal prep I wiped down my entire truck with acetone before installing it.
I put the stuff everywhere and I mean everywhere. I also put it on two layers thick minimum, on the floor of the cab I went with 4 layers on the passenger side and over the transmission tunnel. My exhaust pipe is on the passenger side and my old truck I used Dyna-Mat Extreme along with Dyna-Liner over it and I could still hear the exhaust a bit.
So I didn't want to take any chances on current truck I piled it on. Then I put 1/2" CCF over that along with a 1/4" of a thermal block which was a white foam material with a aluminum foil coating. Then I put Jude over all of that stuff. I had almost 1-1/2" of material on the transmission tunnel itself. I bought a custom plush carpet kit from Stock Interiors and it came with a rubber backing that was almost 1/4" thick. Funny thing was I had to keep putting foam or CCF on the tunnel to get the carpet to lay flat on the floor. So for me the materials were not a problem at all. Was a mother F'er finding the bolt holes for the seats. Then to top things off I installed 1" outdoor CCF with a aluminum sheathing under the entire cab.
I can honestly say my truck is silent going down the highway at 75 mph...... it really is.

As far as your GT Mat coming loose it had to be because the metal was dirty or greasy. I used a commercial heat gun when I applied mine and I heated it to a super soft pliable level and that stuff is on for life.
As far as the makeup of GT Mat goes its 80% butyl and 20% of a asphalt type material and that is only on the face of it for making it stick to the metal. But once you do have it attached properly its not coming off. It is hell to remove which was why they put it into the butyl.
In my case I put so much soundproofing into my truck there was no way it wasn't going to make a huge difference. In the doors alone between the door skins and interior door panels I have a total of 460mil of butyl. Then I have a total of 2" of CCF in there along with that 1/4" white thermal material on back of the door panels.

Is there better products that I could have used....... of coarse there is. But there's no way any other products could outperform my end result. Because of the fact I went so far overboard with the amounts I used, and I encapsulated my cab with different materials.
LOL At least that's what I'm going to believe and I'm sticking to it. Last time I'm going through this too because it takes a freaking lot of time effort and money to do.

Good Luck on the project and good luck on your choices. I must admit Second Skin has a lot of stuff very similar to what I installed. I'm sure its all very good material and they surely know what they are talking about. I would give them a call and let them guide you through the process. Prices looked good as well, Dyna-Mat is more money than its worth IMO.


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## BMW Alpina (Dec 5, 2012)

Marky said:


> That's interesting because I didn't smell any odor at all when I installed it into my truck. As far as sheet metal prep I wiped down my entire truck with acetone before installing it.
> I put the stuff everywhere and I mean everywhere. I also put it on two layers thick minimum, on the floor of the cab I went with 4 layers on the passenger side and over the transmission tunnel. My exhaust pipe is on the passenger side and my old truck I used Dyna-Mat Extreme along with Dyna-Liner over it and I could still hear the exhaust a bit.
> 
> As far as your GT Mat coming loose it had to be because the metal was dirty or greasy. I used a commercial heat gun when I applied mine and I heated it to a super soft pliable level and that stuff is on for life.
> ...


Hi,
I don't use acetone but I did use alcohol to prep the surface,
acetone would eat the paint, I think it is too strong.

but I agree with you that some of the reason my GT mat is peeling off near the engine bay must be because the surface is not that clean...


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## Hohn.Ian (Feb 10, 2018)

Marky said:


> BMW Alpina said:
> 
> 
> > I have GTMat on my door and it leak the asphalt all the time when it's summer... plus it was a bit smelly...
> ...


Just a quick hack in reference to your trouble finding bolt holes:

I guess if you pull the old carpet, it’s pretty obvious how you find them. That’s not what we’re talking about. But in a situation where you don’t have all the previous carpet to go from:

-You’ll need the carpet that has the hardened adhesive on the back, or else a contact cement will have to be used. It has rubberized properties that will allow it to stretch in high temp (same applies to deadened if you want it to stay vertical). Don’t fool yourself into believe gravity will handle it and hold the carpet down.

-do it on a sunny hot-ass day. Much as it sucks. Lay it in the sun adhesive side up, as this will make the carpet easier to work with, and more pliable. 

-Have someone help you lift it into the vehicle. Folding it in half so the glues facing out REALLY helps.

-Starting at the transmission jump and working out towards the doors, use a magnet or your fingers (okay to cheat by looking underneith) to find the bolts. If you removed them with the seats and center console, thread them back into the holes to make it easier to find. 

TIP: Take a socket that’s seen it’s day, afix to a drill, and spin it with a file. Bevel the rim of the socket down to a fine razor edge. Then, stop the drill and use the file of a dremel to put notches along that rim. Like it’s serrated. Then, fit the socket over the bolt in the car floor and give it a second or two on high speed. It’ll cut a perfect hole in the right spot every time. No fray at all, just play with the edge of the socket to find what works. Finally, wait to trim the perimeter unill center console and sears are bolted down. Hen trim kick plate and pop trim back on. Viola’


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