glassing the inside of an MDF box

[d cha p 10+ year member]

I am planning a new box for a new 18" that will be receiving ~2500 watts. I have too use 3/4" mdf because that is the only way too achieve the volume that I want due too space restrictions. I would imagine that the box would flex like a mofo if I used just the mdf so I am planning too coat the inside of the box with fiberglass resin or maybe even a coat of fiberglass. Would doing so have any adverse affects on sound other than increasing spl? I also realize that this will take up volume so is there anyway too estimate how much?

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[Chevyaudio 5,000+ posts]

you dont have to fiberglass, just look into bracing the box internally with some more 3/4 inch mdf or some 2x4 ripped down to 2x2's and when your finished bracing just add the deminsions of your braces together and get their volume and then subtract that from the sub box

 

[bcarpenterfhl 10+ year member]

glassing will take up alot less volume then bracing. however, i would do at least 2 layers of glass because fiberglass isnt very strong when its just a large flat plane. dont worry about accounting for fiberglass displacement, the difference surely wont be audible.

 

[Primo 10+ year member]

i glassed the inside and outside of my box because i used 1/2" mdf for space reasons. came out harder than a rock.

 

[req 5,000+ posts]

or you could cover it with resin, then soak some nylon rope in resin, and stick that in little swirls to the walls of the interior, and use some 1x1 bracing.

thats what id do, maybe just get some threaded rod, and do it that way.

wish i had some pictures for ya but i cant rermmeber where i them before //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif

 

[d cha p 10+ year member]

^that is a good idea. The rope, a couple of 1" dowel rods, and a coat or two of resin should do the trick. Again, this will not have any adverse affects on the sound of the box will it?