Custom Invisible Subwoofer Enclosure for Your Spare Wheel Recess

When I started to install my first audio system, I was in conflict whether to use a subwoofer in my trunk or save the anyway small space. I decided for none of those solutions since I discovered the idea on the internet, of using the space in the spare wheel recess to place the subwoofer. In the picture I did not yet complete the bottom panel. 

The advantages are obvious: You get more storage space and an original looking trunk, while having an awesome sound. 

If you also plan to do this project, I would highly suggest to buy one of those tire repair kits to replace your old spare tire. 

All you need is:
- a subwoofer chassis
- a jigsaw
- a buzzsaw
- MDF wooden panels
- wood glue
- silicone
- damping wool (optional)
- screws
- cordless screwdriver
- time
- a car with a spare wheel recess

Step 1: Choosing a Fitting Subwoofer Chassis

Which subwoofer chassis you should choose depends on the space you have in your spare wheel recess. I roughly measured it out and calculated the available capacity. Now you can compare your volume to the recommended enclosure capacities of your favourite subwoofers.

You also should decide whether to use a closed enclosure or a bass reflex enclosure. The more space you have available the more choice you have. I had only about 22 liters so I chose a Hertz ES250 Energy with 250 watts continuous power which should do for me. You can check the parameter of my subwoofer here.

Once you have chosen your chassis, you can start planning the enclosure.

Step 2: Planning the Enclosure

First of all I made a prototype base out of cardboard to get the ground measures. I then drew many designs on paper and chose the one I preffered most. Afterwards, I set various lengths and replaced the height with a variable and calculated the perfect height to get my desired capacity.
One struggle I had to deal with was the annoying pin which lifted from the ground.

Another way of building the enclosure would be using fibreglass, but since I have never used this technique before I started with the easier one. The advantage of the fibreglass method is that you can exploit all of the available space and must not struggle with determined forms.

Step 3: Sewing Out the Parts

Once you finished planning your enclosure, you can go buy the stuff you need.

I used 3/4 inch MDF panels (medium-density fibreboard) but I think anything likewise will do. Most square parts had been cut by the hardware store. The only thing I had to do was cutting the angles with a pivoted buzzsaw. Be careful when using the jiggsaw. It might easily go wrong.

Step 4: Gluing and Sealing

Besides gluing the panels with wood glue, I screwed the plates together to make it end up more solid. I noticed that screwing MDF plates without pre-drilling them is not as funny as it sounds. But luckily you learn from mistakes.
When the basic enclosure was finished, I started sealing the edges with silicone.
Don't forget to cut out the circle for the subwoofer chassis. Once that the glue dried, I gave the enclosure a last finish by sealing the edges from the inside and the outside and finally drilled a hole for the subwoofer cable on the top.

Step 5: Mounting the Components and Testing

When I finished my enclosure I inserted the damping wool and mounted the chassis as well as the amp. The damping wool virtually increases the volume of the enclosure by slowing down the sound waves inside the enclosure.

I'm quite satisfied with the result in my car. The closed enclosure produces rich and clear bass and due to the fact that the enclosure suits very tight on the pin, it transfers the vibration very well to the car's body. The best thing about it is that I am able to use my whole trunk, at least if I can manage to build the ground plate in the next few weeks.

I hope you enjoyed my instructable and got animated to start a project by yourself.