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Studdlygoof 07-23-2011 04:33 PM

1995 Ram 1500 Custom 12" Underseat Subwoofer Enclosure Build
3 Attachment(s)
Well with my futile search of a box that would fit under my rear seat for 2 12" subwoofers I have decided to build my own. I had first considered using MDF as a building material, but with my minimal amount of space already I have decided to build a fiberglass enclosure to maximize the amount of space.

As many of you already know there are a lot of curves and angles under the rear seat so I decided to fiberglass the entire bottom of the box as well to make my life easier. My carpet is still in pretty good condition and I don't want to risk a "mishap" that would ruin it. I stopped by the local junk yard and two hours later in 105 degree weather I was able to pull the carpet out of 1998 ram that matched mine.

After giving it a good cleaning with a shop vac, I cut it in half with a pair of tin snips. Next I removed the rear seat and seatbelt holders I placed the carpet in the back and made a few more cuts to make it fit.

The carpet is still a little lumpy from being pulled out but i'm going to get a couple sand bags to lay ontop of it and I think with a couple of days in this heat in should be back to its normal shape.

Next step is going to be taping up the back wall and side panels and apply the bottom layer of fiberglass. My plan then will be to remove it once it dries and start working on the overall shape and dimensions required for air space. For now though there is a local beer crawl down at the college so I'm calling it quits

Any suggestions or comments are greatly appreciated as this is my first time building a box with fiberglass. More soon to come

RedRam10 07-23-2011 04:40 PM

Nice start to a work in progress. Keep us posted. :rep:

Join our red ram group and drop by the newbie checkin - both links are in my SIG below.

Studdlygoof 07-24-2011 09:16 PM

3 Attachment(s)
Had some more free time today so I decided to work a bit more on the truck. After running all over town for supplies I finally aquired everything I needed to start fiberglassing the base of the box. Just to make my life a bit easier when it came time to remove the fiberglass from the floor of my truck I decided to line it with tinfoil. This is definately a feat that is definately a lot easier then it looks. Every time you lay down one sheet and move on to the next the previous one is out of position. With some persistance and a couple rolls of tape later I finally got it all layed out. I then taped up a painters tarp around the surrounding wall and over the front seats to keep clean up to a minimum.

I purchased both fiberglass cloth and fiberglass mat to add to the bottom. From what I read the fiberglass mat is used for more structual purposes while the fiberglass cloth is easier to wrap around tight corners and details and is more for athetic purposes. My goal is to lay down two layers of the fiberglass mat as a base. Then lay down some nylon rope in a grid pattern to make the base even more rigid. I read on another forum that the nylon rope will soak up the resin and get as hard a dowel rod while attaching itself to the fiberglass giving you a sort of impregnated structure support. Over top of this I am going to lay a layer of the fiberglass cloth. I think that these three layers will be enough for a base.

I mixed up my first batch of resin and hardener as per the directions and learned my first quick lesson in what not to do with the resin. The directions say it is better to work with small batches at a time because of the setup time of the resin is short. Well my idea of a small batch was obviously not small enough because within a minute my plastic mixing cup got too hot to hold and hardened up like a rock. I dumped it on a piece of plastic and it actually melted through the plastic while it smoked and bubbled :doh:. Scaling back my proportions I was finally able to get some actual work time with the resin. Taking the 2x6 strips of fiberglass mat I piece by piece covered my tinfoil mold while dabing on the resin with a paint brush. Gloves are definately a must and a well ventilated area cause the stuff stinks to high hell.

It took me about an hour to get the whole surface done with one layer. Two hours after that I have a hard base coat of fiberglass that already is pretty rigid. Hopefully tommorrow I will be able to get the other two layers done so I can get the base out of the truck. I left the doors and all the windows open in the truck all day and it still is pretty potent in there. Thats all for now; hopefully I will be able to get some more pictures uploaded of the progress.

Studdlygoof 08-08-2011 10:06 PM

I'm way behind on updating this build; coupled with a week vacation and a week long sinus infection progress has still been made. Since my last post I have reinforced my original layer of fiberglass by criss crossing 3/8 nylon rope along the bottom. I have been reading up a lot on fiberglassing subwoofer boxes since I am new at this and have seen people in other forums use this nylon rope over flat surfaces to make it more rigid. When the resin soaks into rope it hardens like a dowel rod. After laying all the rope I used painters tape to help hold it all down while fiberglassing

I then layed two additional layers of fiberglass mat ontop of this. This is a major PITA trying to keep all the bubbles from forming under the glass.

I was running out of light so the picture is a little dark but this is the finished product.

Studdlygoof 08-08-2011 10:36 PM

After letting the last two layers of fiberglass dry, the entire piece was rigid enough to remove from the truck. There is a total of 5 layers of glass right now with nylon rope in the middle. After I get all the MDF sides done my plan is to come back and add a couple more layers to the specific "box area" to make it even sturdier.

Now that the piece was out I needed to trim it up a bit so that I could get some better measurements for my MDF sidewalls. I see alot of people use jigsaws when cutting their fiberglass boxes. With all the contours on my piece i was worried I wouldn't get a good clean cut with all the vibrations. After a quick trip to Home Depot I found a cutting blade for my Dremel that was made for fiberglass. Other then the massive amounts of dust, this blade worked 10 times better then I wanted it to. I was able to get nice clean fine tuned cuts in a rather quick time.

With the bottom all trimmed up I was able to finish the final details with the actual enclosures for the woofers. I'm going with two Crossfire DB3 12" Subwoofers. I lost the paperwork for them somewhere in a move and couldn't find any of the specifications for the cubic air space required for each sub to work properly. I ended up calling the technical support technician at Crossfire and he told me that they require optimally 1 cubic ft of airspace per woofer. I then added another 15% of space ontop of that to make up for the displacement of the woofer itself so I end up with 1.15 cubic/ft per enclosure.

dru22 08-08-2011 10:57 PM

Great writeup so far- interesting stuff!

Studdlygoof 08-08-2011 11:07 PM

Throughout the process of making my MDF sidewalls I have learned a lot of lessons and wasted a lot of wood. There is nothing square with this box and a lot of complicated angles. I tried cutting each piece exactly to size, but every side piece is different because of the nylon rope on the bottom and the curves are different so they ended up being way off. Starting over I cut my pieces way oversized and freehanded the contours on each panel. After 1/2 a day of total fustration and a lot of saw dust from cutting and filing all I ended up with was this.

I spent the rest of that night enjoying a few more of those beers and trying to come up with a better and faster way to get the rest of my panels made. It then hit me that this is no different then using a profile scribe to transfer baseboard and custom crown moulding onto an adjacent piece.

So refreshed and renewed with a new game plan, I started the next day and came up with a make shift profile scribe. Taking a 1/4" piece of venier I had left over I clamped it to two small vises along a line where the panel would be.

I then took a pair of ID calipers and taped a pencil to them and keeping the pencil directly over the tip of the caliper I traced the contour onto the piece of venier

With this line I was able to cut it out with a jigsaw and then use it as a pattern to trace on my 3/4" MDF.

The final product was a panel that fit better then my freehanded pieces and was done in 1/4 of the time. I was able to get the rest of this done in 2 hours verses the 6 I had wasted the day before. Lesson well learned.

The four cross braces are just temporary support for the time being and wont be on the finished product. I nailed all the pieces down temporarily so that I can get a better visual as well as get a good level line along the top of the pieces to ensure they are all the same height in the end. You can see the excess left on the heigth of the pieces. The subwoofers will sit in the two outside enclosures and the amp with sit in the center. Next on the list is the trim the pieces to size, added a rounded radius to the front top corner of each piece and router a radius on all the outside edges. More to come in the upcoming days.

Studdlygoof 08-20-2011 02:59 PM

Quick update on my progress. Stopped by the local audio shop and picked up my amp. Decided to go with an 800 watt Orion Cobalt amp to power my two Crossfire DB312 12" Subwoofers. Excited to hear what they sound like.

In between all the scattered thunderstorms I was also able to finish trimming up all my MDF sidewalls for the enclosure and get a routered radius on them. Then they got glued and screwed. Definately drill pilot holes in all pieces that get screwed together. Even with my pilot holes I had a couple pieces split on me.

I planned on attaching the MDF sidewalls to the fiberglass base with screws as well but after a little though I was worried about the screws pulling through or cracking the fiberglass with the constant vibrations over time. Call me worry wart if you want but I would rather be pro-active to this problem now rather then reactive to a problem on down the road after everything is installed. To spread out some of the pulling force of the screws over a wider area rather then a focused one I decided to make brackets to cover the area that would be screwed to the MDF. To do this I took 1" aluminum flat bar that was an 1/8" thick and cut pieces to fit. I then drilled pilot holes for the screws every two inches and countersunk them for the screw heads.
In the end the flatbar ended up working better then I thought and gave me a really rigid setup. The bar bent nicely along the curves of the fiberglass base and sucked the sidewalls down tight to the fiberglass.

My next step for today is to get an amp rack cutout to fit between the two woofers. Since I am going with a sealed amp rack in my design I stopped and got two 3" 12v computer fans to install in a push-pull setup for cooling of the amp. I also plan on sealing up the woofer boxes with some caulking and add a couple more layers of fiberglass to the inside of them to make sure i've got a good tight seal and a little bit more rigid.

More to come as progress is made

Frank Drebin 08-20-2011 07:10 PM

Great thread. I will steal some of your techniques when I attempt my first fiberglass box.

Quick question: Why didnt you attach the mdf to the fiberglass with fiberglass instead of screws? Please update this thread. Again, great info.


Studdlygoof 08-20-2011 09:17 PM

Quick question: Why didnt you attach the mdf to the fiberglass with fiberglass instead of screws?

Frank, as with most things in this build I probably over due it, but the main reason is I wanted to keep everything square. Also I think the structure wouldnt be as strong and have a risk of just sliding off the MDF over time. With all this in mind, however, now that the MDF is attached to the base I am going to go back and fiberglass up the inside walls of each enclosure before I add fleece to give myself an airtight enclosure

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