# Open cell egg crate behind door speaker...



## bchandler (Jul 30, 2007)

Hi guys. I used some open cell egg crate packing foam that I picked up from work inside my doors behind my speakers. I sealed the uncut sheets with that camping waterproofing spray from Wal-mart, but afterwards I cut it to fit, so the sides are unsealed. I am worried about this foam holding water and damaging my speaker, or growing mold. Are car audio speakers engineered to take the harshness of the environment? I was careful to leave the doors' drain holes unplugged.

Is this foam even doing anything for me? (I have not yet hooked them up). Should I pick up some bona-fide acoustical foam from a supplier and use that instead (though I cannot seem to find closed cell acoustical foam for use behind the speaker... egg crate, wedge form, etc). Or will my speaks sound great without anything behind them (besides the 3 layers of Raammat of course )? It will be a lot of work to remove the foam, so I want to make the right decision.

My door also has a round support bar running horizontally right behind the speaker horizontally, affixed to the outer door skin. How do I deal with that, or will it's cyclindrical shape prevent reflections naturally?


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## dBassHz (Nov 2, 2005)

I use a blue camping ground pad (closed cell egg crate shaped) that I found at Walmart for approx. $11.

Here's a picture of it early on in my install.


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## bchandler (Jul 30, 2007)

Yeah, I saw that at walmart as well. I didn't buy it because the pattern does not look deep enough to do anything. At work we had several types of egg crate, some very shallow and some quite deep. The deep egg crate absorbs sound much better when held close to the ear. If you look up real acoustical egg crate you will see that the egg crate is also super deep. Plus the texture of the material and lack of mass on the camping pad wouldn't make for very good acoustical mat, in my opinion.

Rick from Raamaudio told me to only use a product right behind the speaker as well. Does anyone have any input on that? I know he knows his stuff, but it seems like using it over maybe half or 1/4 of the door's surface (corner with the speaker) would absorb random waves much better.

I think I am going to source some real acoustical egg crate foam or wedge-form foam, but I really need a way to seal this stuff 100% and never have to worry about water. When I took my old Crystal mids out from my old install they were rusted! And I do not want that to happen to these new Rainbows.

I am also going to try to use the tupperware method by using a silicone caulk line and sticking them onto the door behind the speaker to block water directly dripping onto the speaker.

Please help!


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## azngotskills (Feb 24, 2006)

Do you think that treating open cell foam with a waterproof coating will affects its ability to absorb sound? If so, are the gains over closed cell foam in regards to absorption worth it then?


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## Oliver (Jun 25, 2007)

Why not use the http://www.mainstreet-audio.com/Mer...en=PROD&Product_Code=D7&Category_Code=CASCADE

they are waterproof, diffuse the sound pressure waves thereby allowing you to crank it up a lil bit more before it distorts.


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## FoxPro5 (Feb 14, 2006)

IIRC, Rudeboy has said that part of the effectivness of deflex-type pads is the mass loading and vibration reduction of them on the door skins.

If you think about it, you need to absorb 100% of the rearwave in the passband of the driver. So for a driver that's playing 63 hz to 2k, for example, you'd need it to be pretty thick to kill the lower octaves. The uppers will probably do fine with 1/8" CC or OC foam.

I think the OC foam you're taking about is designed for room reverb and echos, not to take a stright shot of music from 6". 

Here's my real world experience tied in to a short review.
- Installed 8" dedicated midbass drivers in my front doors along with a pre-existing sandwhich of Damplifier Pro and Over Kill. Drivers HP at 50 hz with a 36 db/oct slope.
- Played "Take The Power Back" off of RATM's self-titled. This track has incredible snap and power from bass guitar and kick bass combined in the first 30 seconds. It should be dead center in you stage and punch you in the chest like a mofo.
- Results: Extreme snap and ok low end extension. 

- Took 1" OC acoustical grade foam and glued it on top of the DP-OK sandwich. Not the egg crate type, but the flat type.
- Played track again
- Results: Very little snap. Driver sounded choked. Low end extension improved by 50%.

- Removed 1" OC acoustical grade foam and put in the infamous blue Wal-Mart camping pad (waterproof CC foam).
- Played track again
- Horray! The snap is back, but slightly less. Low end extension is not as good with 1" OC foam, but improved by 25% over nothing.

So, for me the blue pad stays and the OC foam goes. I'm taking the edge off the snap slightly, but part of that effect might actually be the rear wave hitting the door skin too? Not sure. But I'm getting better lower end performance out of the mids as I would't have otherwise.


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## FoxPro5 (Feb 14, 2006)

double post, sorry


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## FoxPro5 (Feb 14, 2006)

No I did not treat the foam. And yes it did get wet and retained water when it rained. I don't recall seeing water on my drivers in my doors...in as many as I've had in there.


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## bchandler (Jul 30, 2007)

Thanks for the advice thus far. 

I'm still not convinced the actual egg crate pattern on the wal mart pad helps, I think it is the sound wave diffusion through the actual material before it hits the solid door panel. But if it works, it works. So you're saying the blue pad was a compromise between faster response and low end extension? IE, you get better of one or the other with acoustic foam and 1/8" CC, but the blue pad gives a blend, albeit less of both, than either or? 

B-squad- are you also saying with regards to not treating the foam, that the moisture of the foam has little to do with damage to the driver? Does damage come more from water dripping directly onto the speaker from the window seal? How long did you have the OC in for and what is the climate like? Notice any mold?


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## FoxPro5 (Feb 14, 2006)

bchandler said:


> Thanks for the advice thus far.
> 
> I'm still not convinced the actual egg crate pattern on the wal mart pad helps, I think it is the sound wave diffusion through the actual material before it hits the solid door panel.


I agree.



> So you're saying the blue pad was a compromise between faster response and low end extension? IE, you get better of one or the other with acoustic foam and 1/8" CC, but the blue pad gives a blend, albeit less of both, than either or?


Definitely a compromise, yes. I can say, without question, that in my install and for my $$$ the 1" OC "acoustical" foam is a rip! Like I said, I felt like it choked the driver. 



> B-squad- are you also saying with regards to not treating the foam, that the moisture of the foam has little to do with damage to the driver?


No, I'm saying that the OC foam I used sucked up the water that I got in my doors like sponge...possibly keeping it away from the driver. I've had lots of drivers in my doors and none have suffered water damage. Yes a few rusty terminals, but nothing major.



> Does damage come more from water dripping directly onto the speaker from the window seal? How long did you have the OC in for and what is the climate like? Notice any mold?


The water got in the door when I rolled down the windows on a rainy day. Since the foam was 1" thick and I had at least 3/8" of deadener and CC foam on before it, the window was very close to the foam. So, the rain that was on the bottom of the window soaked the foam over time.

I had it in for maybe two weeks. There was maybe 3-4 rainy days in there. Again, don't roll down your windows when it rains and I think you'll be fine.

No mold, not enough time.


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## tdgesq (Apr 16, 2006)

If you're worried about water saturation, just take a hose and douse it on the side of your window for a couple of minutes. That's what I did, and I could see exactly where the water came in and how much it affected the acoustic pad. In the case of my rig, it didn't do much.


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## AwaySooner (May 30, 2007)

I used the same type of pad but from secondskin. 7" is really tiny for 6 1/2 speaker, if I knew how small they are, I would've pay more to get the 12"x12" instead. 



Hic said:


> Why not use the http://www.mainstreet-audio.com/Mer...en=PROD&Product_Code=D7&Category_Code=CASCADE
> 
> they are waterproof, diffuse the sound pressure waves thereby allowing you to crank it up a lil bit more before it distorts.


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## bchandler (Jul 30, 2007)

Well, it rained a bit during my install, and the open cell egg crate was pretty wet. I guess my doors aren't sealed too well to the elements. 

I'm really having a hard time deciding if I should leave the foam that's in there now or change to a deflex type pad or wal-mart pad. Arrrgh...


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## bchandler (Jul 30, 2007)

tomorrow is when I'll be pulling the speakers and doing the tupperware water guard over the speaker. Now is my time to change the foam, as well. Lets hear those last opinions! (please? ) I really don't want to open the doors again after this for a long while.

I'm going to go with some wal-mart pad if no one else chimes in... I may also pick up some real acoustical foam to use in the car in other places like behind panels and the dash, to see if it makes a difference.


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## Oliver (Jun 25, 2007)

bchandler,

I guess you need to install this based on your comments.
http://www.mainstreet-audio.com/Mer...=PROD&Product_Code=SK-2&Category_Code=CASCADE
It allowed Ted to maximize the JL Audio 300/4 in his F-350 with a diesel ! 

When Aaron tuned it after the install, Ted and I stepped outside the garage to talk and we could still hear the music loud, really loud and clear !!


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## FoxPro5 (Feb 14, 2006)

Not sure if you caught it in my last post, but _I_ personally believe, after using good stuff and generic crap, that "acoustical" foam in no more acoustical than the gas in your tank is "car" gas. 

How do you answer this question you are dying to know? Trial and error.


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## Abmolech (Nov 2, 2006)

It is close to a waste of money, you may gain mass loading (changing resonant frequency). Absorption is directly depended on diffraction, IE it has to make the wave pass through a convoluted or labyrinth path way to loss energy in the form of heat. The frequencies of these drivers prohibit useful gain to be made on something so thin.The driver uses SIGNIFICANT amounts of energy to change mechanical into acoustic energy, how much energy do you think a thin absorber like those can exact to heat?


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## tdgesq (Apr 16, 2006)

bchandler said:


> Well, it rained a bit during my install, and the open cell egg crate was pretty wet. I guess my doors aren't sealed too well to the elements.
> 
> I'm really having a hard time deciding if I should leave the foam that's in there now or change to a deflex type pad or wal-mart pad. Arrrgh...


FWIW, I used the same blue wal mart pad that is shown here: http://www.diymobileaudio.com/forum/showpost.php?p=211329&postcount=2

I can't really tell you whether open cell foam would provide an audible difference or not. I wouldn't make my choice based upon mass loading though. Just put on another layer of raammat if you want that. If you go for closed cell foam, you won't have to worry about moisture.


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## FoxPro5 (Feb 14, 2006)

Waterproof
Closed cell
Cheap
Effective










Water retentive
Open cell
Expensive
Somewhat effective


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