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fiberglassing question

Old 08-14-2012, 06:32 PM
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fiberglassing question

i'm attempting my first FB box build. This is for a rear trunk corner sub. I've built the form that fits in the trunk, placed the baffle rings and fleeced the front part of the box now. i'm wondering how the joint where the fleece meets the 'trunk form' and where the fleece meets the baffle rings should be glassed.

1. between the trunk form and the fleece I can't put extra resin or mat on the outside or i'll build up material and the box won't fit in the trunk properly.

2. between the baffle ring and the fleece there isn't a lot of contact area on the outside for resin contact area. i didn't use a ton of dowels so the glassed fleece will have to support some of the weight (as well as being a good seal).
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Old 08-17-2012, 04:39 PM
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Take the box out and glass the baffle outside of the car. If some glass gets on the rear mould you'll have to cut/sand/grind it away/down to make things fit back in. I would make sure that your front baffle (and the entire box for that matter) is made up of LOTS of layers. I would not only add in some more dowels, but also some internal bracing. Subwoofer boxes need to be SOLID. One trick I've heard of is to resin in some strips of hemp or cloth rope every 6" or so to act as rib bracing on a surface. I plan on using a combination of plywood and fiberglass on my next box to get very stiff results.

To give some idea of the forces at work, try holding onto your subwoofer while it's turned up and playing some heavy bass. There is a lot of shaking going on and I bet you won't be able to hold it still. Build a rock solid box that will, or you'll just be disappointed in the results.

Last edited by stochastic; 08-17-2012 at 04:41 PM.
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Old 08-17-2012, 08:47 PM
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Reinforce from the inside. Take a litre of resin and add cut up pieces of mat to it until it is thick but still flows alright. Add the hardener, stir, pour it through the woofer opening and then roll it around inside the box, coating the fleece and filling in where the fleece approaches the baffle ring and the glassed rear half of the box. Keep rolling the glass around until it sets up - mix the glass on the hot side so this doesn't take forever. Repeat as many times as you need to until you think it's strong enough. After the first or second application you can probably add strips or squares of mat through the woofer hole as extra reinforcing.

I have done this for kickpanels and woofer baffles. Works great and the best part is there is no sanding. Personally I laugh whenever I see a FG build and the poor schmuck has added a bunch of glass on the outside and then has to sand 1/4 of it off to try to get it smooth again..
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Old 08-18-2012, 09:37 PM
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well i actually finished this before either of the replies. what i did was paint the joints between the fleece and the rear box on the inside with a couple layers of resin and then added a few layers of mat and resin on the inside at the joints. the baffle face was then glassed with a few layers of mat on the outside. i think it should be strong enough now. i ran out of budget for resin so it will have to do for now. i did reinforce flat areas with wood braces and glass those in as well.

dukk, i can understand painting the inside of the box with resin, or even rolling resin around but it's an incredible pain to try to put down mat on the inside of the box. the stuff just gets everywhere on your hands and arms. outside is more work later but a lot less messy. since i'm not painting the outside of the box i was pretty messy with the exterior glass but it won't matter much as i'm covering it with foam which should be more forgiving than carpet even.
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