One of the most satisfying upgrades you can make to a simple system is the addition of a subwoofer. The low bass a subwoofer can provide will greatly enhance the musical experience in a car, even one with an otherwise factory system. We've used our Volvo S60 project car in a few articles already with the head unit and navigation screen installations. This month, we'll show you how to install a simple 10" subwoofer system in the trunk of the Volvo that won't take up any space. The technique we'll use for this sub system allows you to form odd-shaped subwoofer enclosures very quickly. Needless to say, we use it often. This month, we'll make the back of the enclosure and form the frame for the fiberglass on the front. Next time, we'll finish off the fiberglass and add the finishing touches to integrate this enclosure cleanly into our Volvo. As always, send any questions to sbrown@alpine-usa.com and check out SteveBrownUniversity.com for more hands-on opportunities.
Here's the stock trunk area of our Volvo S60 sedan. | 
Our first order of business is removing the stock trunk liner in the mounting area to see what's behind it. | 
The procedure for making the sub enclosure involves cutting individual pieces of wood to fit together like a puzzle. |
Here, we've taken the cardboard and transferred the shape onto our 1/2" MDF sheet. | 
We also need to consider how to mount this enclosure in the car after it's finished. | 
Next, we'll use the same technique to make all the rest of the pieces for the enclosure. |
This shot shows some of the strange shapes that emerge when forming a box to fit an odd-shaped space. | 
With a few more pieces in place, we end up with the complete bottom, top, back and sides for our sub enclosure. | 
We can now use an angle die grinder to trim off any sharp edges on the back of our enclosure. |
Before we install the top of our enclosure, we need to reinforce it. The CA-glue we used to hold the box together is just a temporary bond. | 
The reinforced body filler is simply stuck to all the interior corners of our box, a procedure that both strengthens and seals the joints. | 
Now it's time to make the front of our subwoofer enclosure, so we have to decide if we want to use a simple flat top or spend the time to make a more stylish curved fiberglass panel. |
A neat trick that we use often is to make our subwoofer ring out of two individual rings glued together. | 
An MDF brace is required on the front of the box to stiffen the structure, so here we are attaching one with CA-glue. | 
Now we have our sub enclosure framed out and ready for fiberglass. We'll finish this project up next month. |