# sound deadener to line a subwoofer box?



## milburyl (Feb 23, 2014)

I just built a sub enclosure out of 3/4" plywood. It's what I had on hand and was cheaper than mdf. I wanted to use it to kinda get an idea of how my subs will sound in it before I go ahead and make one from mdf. Or maybe an mdf one won't even be necessary if I can solidify this box a little more.
Question is, will sound deadening applied to the inside of the box do a good job of studying it up?
Or should I mix up some fiberglass resin (just the resin) and brush it over everything inside the enclosure and maybe even the outside as well?
The box I built has inside dimensions of 15.75"×20.75"x40.5", so that equals out to roughly 7.6ft3. The subs are JL 18W6's. So is 3.8ft3/sub adequate? JL calls for 1.75ft3, but that seemed really small for an 18" sub.


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## PorkCereal (Nov 24, 2009)

My thought is probably not. Maybe spray on truck liner? Is what comes to mind


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## milburyl (Feb 23, 2014)

PorkCereal said:


> My thought is probably not. Maybe spray on truck liner? Is what comes to mind


I was thinking about bedliner too. Maybe spray the bedliner over the fiberglass resin. I have seen boxes built with sub-par materials before coated with resin on the inside with good results, but they were also in low powered setups. I plan to use a JL Slash 1000/1 to run the 18W6's with. I'm excited to hear what a pair of 18's will sound like. I know a single 15" can produce a ton of bass, and the 13W7 I have in my car with 1000 watts is insane for a single sub. I wanted to build a ported box for the 18's, but JL doesn't recommend ported for the 18W6's, only sealed. According to the JL "cheat-sheets", a 3ft3 sealed enclosure gives a QTC of .77, and the 2.75ft3 gives a QTC of .79, so im assuming that 3.8ft3 will give me a QTC of .71.
What exactly is the QTC measurement? And what should I be aiming for? I have an idea, and generally lower is better, to a point.


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## seafish (Aug 1, 2012)

NOthing wrong with using high grade plywood to build a sub box. That being said, the fiberglass will help seal and stiffen it, , particularly if you add some mesh to it as well, while the MLV will do nothing other then add some density, which isn;t a bad thing, but Stiffer=Better in terms of sub enclosures.


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## SkizeR (Apr 19, 2011)

deadener or resin wont stiffen it. you would need to brace it.


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## seafish (Aug 1, 2012)

SkizeR said:


> deadener or resin wont stiffen it. you would need to brace it.


Resin with matting WILL stiffen it, though braces also work well. Smaller boxes do not necessarily need braces, though larger ones will always benefit from bracing.


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## SkizeR (Apr 19, 2011)

seafish said:


> Resin with matting WILL stiffen it, though braces also work well. Smaller boxes do not necessarily need braces, though larger ones will always benefit from bracing.


with matting.. maybe. would depend on how much. 1 or 2 layers wont really do anything if the box has flex from the start.


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## ruizal (Aug 4, 2015)

SkizeR said:


> deadener or resin wont stiffen it. you would need to brace it.


I'm with skizer on this one. With a box that large and made from plywood of questionable quality I would think some bracing is in order. 

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## axipher (Oct 7, 2015)

ruizal said:


> I'm with skizer on this one. With a box that large and made from plywood of questionable quality I would think some bracing is in order.
> 
> Sent from my HTC One_M8 using Tapatalk


Definitely add some internal bracing, it never hurts even on small boxes.

As for the Resin and bed liner, I've been building boxes out of birch and Pine lately and always throw one layer of fiberglass mesh and resin on the outside as more of a waterproofing so that the wood doesn't absorb moisture and warp.

Carpet is pretty cheap though, but bedliner does work and for some builds, it might fit the rest of the look better.


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## seafish (Aug 1, 2012)

ruizal said:


> I'm with skizer on this one. With a box that large and made from plywood of questionable quality I would think some bracing is in order.
> 
> Sent from my HTC One_M8 using Tapatalk


My bad, misread the the dimensions... you guys are absolutely correct, with a box that large, fiberglass resin will sell the box, but even with matting, will do little to stiffen it ... internal bracing will be crucial.


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## milburyl (Feb 23, 2014)

Thanks guys. Will put a couple braces in it, and resin to seal it up good.


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## High Resolution Audio (Sep 12, 2014)

Fiberglass resin is useless without cloth, tape, micro bubbles, matting, carbon fiber, or roven. It has no strength to it by itself, and will chip and crack.

The glass fibers it what adds the strength. 

You should add PL adhesive or a good quality silicone to seal the edges, not resin alone.

Better yet, put a plywood divider so each sub has its own chamber. Then use resin and two layers of glass cloth on all edges and seams. That will make for one very strong box.


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## chasinbass (Jul 23, 2014)

High Resolution Audio said:


> Fiberglass resin is useless without cloth, tape, micro bubbles, matting, carbon fiber, or roven. It has no strength to it by itself, and will chip and crack.
> 
> The glass fibers it what adds the strength.
> 
> ...


Not to derail thread but I am working on a lager box Acually its done and its for 2 18" Fi team subs and its about 14 cubes out of birch ply and has internal pipe bracing and I just siliconed all the inside seams. Its put together nice as I took my time and have some skills in carpentry so there was no gaps to begin with but my question is should I fiberglass the inside with glass tape and resin ? Will I get any benifit ?

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## High Resolution Audio (Sep 12, 2014)

chasinbass said:


> Not to derail thread but I am working on a lager box Acually its done and its for 2 18" Fi team subs and its about 14 cubes out of birch ply and has internal pipe bracing and I just siliconed all the inside seams. Its put together nice as I took my time and have some skills in carpentry so there was no gaps to begin with but my question is should I fiberglass the inside with glass tape and resin ? Will I get any benifit ?
> 
> View attachment 107465
> 
> ...


That box looks very strong. Really good carpentry skills and bracing. 

If you glued and screwed all the seams you will be fine, assuming you used a good quality wood glue.


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## milburyl (Feb 23, 2014)

High Resolution Audio said:


> Fiberglass resin is useless without cloth, tape, micro bubbles, matting, carbon fiber, or roven. It has no strength to it by itself, and will chip and crack.
> 
> The glass fibers it what adds the strength.
> 
> ...


Thanks for the info. I have already siliconed all the seams and used silicone in between everything before screwing it all together. The box is too far together to try to divide it into 2 chambers now. It was built with a 2"×2" frame and plywood stapled, and screwed onto to 2x2 frame. I can only put braces in now. But I plan to put 2 2x2 braces in between the subs in the middle of the box. I have some fibreglass sheets, so I may do all the edges and seams in fibreglass too, but I am going to brush the resin over the whole inside and outside to help seal it and give it some sort of waterproofing.


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## bugsplat (Nov 7, 2014)

I added bedlinner spray inside and out of my small 1cf mdf box not for strength but to protect from moisture.


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## chasinbass (Jul 23, 2014)

High Resolution Audio said:


> That box looks very strong. Really good carpentry skills and bracing.
> 
> If you glued and screwed all the seams you will be fine, assuming you used a good quality wood glue.


I used Titebond glue always had good luck with it and its screwed and glued. So skip on the fiberglass ?


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## High Resolution Audio (Sep 12, 2014)

chasinbass said:


> I used Titebond glue always had good luck with it and its screwed and glued. So skip on the fiberglass ?


You don't really need it, in your particular build.


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## chasinbass (Jul 23, 2014)

High Resolution Audio said:


> You don't really need it, in your particular build.


Thanks for your input. Some pics of it completed.Should get loud lol

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## High Resolution Audio (Sep 12, 2014)

milburyl said:


> Thanks for the info. I have already siliconed all the seams and used silicone in between everything before screwing it all together. The box is too far together to try to divide it into 2 chambers now. It was built with a 2"×2" frame and plywood stapled, and screwed onto to 2x2 frame. I can only put braces in now. But I plan to put 2 2x2 braces in between the subs in the middle of the box. I have some fibreglass sheets, so I may do all the edges and seams in fibreglass too, but I am going to brush the resin over the whole inside and outside to help seal it and give it some sort of waterproofing.


The resin will soak into the wood. Especially the first layer. You can always brace it with galvanized pipe as chasinbass did. The 2x2's should do the trick too!

Some brands of silicone such as Geocil adhere to wood and make an incredible bond. Other brands can be easily peeled off when hard. Check yours to see how it grabs on to the wood. If if comes off easily or if you have any doubts, a couple of layers of fiberglass resin and cloth on the seams only. You could use a peel and stick or spray on bed-liner if you wanted. You can also add fiberglass insulation or fiberfill in the cavity if you wanted to go all out.


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## High Resolution Audio (Sep 12, 2014)

chasinbass said:


> Thanks for your input. Some pics of it completed.Should get loud lol
> 
> View attachment 107489
> 
> ...


Really nice finish too! You missed your calling.


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## chasinbass (Jul 23, 2014)

High Resolution Audio said:


> Really nice finish too! You missed your calling.


Nah I am old and I am slow lol ! prob wouldnt make much money that way!
I just really like doing it and thats most of the fun.


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## sqshoestring (Jun 19, 2007)

Get something like 3M 5200 if you want to get serious, though I never seen a need for it. Its polyurethane, its like a little harder silicone and bonds much better. Im sure it can be found under different names. Its the stuff that holds your windshield in but that kind is black. It is permanent, you can make rope out of it that is how tough it is.

For fiberglass to make ply strong you need to mat both sides, that creates a laminate because the skins of glass do not stretch. That is how boats are made, its very stiff and strong, its like making the ply (or whatever core material you have) into an "I" beam for a simple example. The ply would be much stronger. Bracing would be easier for a sub box far as strength.

I have added mdf to sub boxes by lining them or facing them just to deaden, but not often. I have glued 1/2" onto 3/4 ply. But I make most all my boxes from ply because its strong and holds screws so much easier to work with, slightly lighter maybe. Though I tend to work on less than 1kw sub systems.

Deadening is sort of pointless with sub boxes unless you are polyfill (or similar) inside the box to tune it lower for sound, not for structural reasons.


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## High Resolution Audio (Sep 12, 2014)

I myself, use PL Construction Adhesive to bond and seal all my seams. I use 3/4" ply for small enclosures.


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## chasinbass (Jul 23, 2014)

I will try that next time , I have used it in construction and it is some strong stuff


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## Jroo (May 24, 2006)

on the 18w6 it can play in the 1.75 but you lose a bit on the low end. I found the tech sheets and JL had cheat sheets years ago. After looking at those and having a few model them that used them years back, 2.0 to 2.3 sealed ended up being the best. I still have one left from the Credence build a few years ago. I would do the 2.3 sealed to get the most low end out of it, if you can give up the space.


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## 63flip (Oct 16, 2013)

I would really like to hear what size you settle on and the final construction. I've got a pair of 18w6's that I'm thinking about filling the extended cab of my old Ford Ranger with in the spring. If I do decide to run them I'll probably be using OS Lanzar Opti's for power.


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## milburyl (Feb 23, 2014)

The box is built already. It's 7.6ft3 altogether. So about 3.8ft3 each. If that is too much, I can put something inside the box to use up some space.


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