Tutorials: Building a Subwoofer Enclosure
- Tuesday 15th February, 2011
Buying a pre built subwoofer is easy, but you can often get a better and more integrated result if you build it yourself. There really is more satisfaction to be had by building a subwoofer enclosure yourself - primarily the sheer fact of the being able to sit back and listen to the glorious bass response happy in the knowledge that your own sweat and toil was part of the equation. Here's how ...
Talking of equations, building your own subwoofer enclosure does require a little bit of math. For any subwoofer to work well it needs to be placed into the correct size enclosure. To keep things simple I’ll stick with the basic sealed enclosure design since it’s the easiest and cheapest to build and, quite frankly, you’ll have a pretty hard time stuffing it up. That’s because for modern subwoofers you can be used in 20% over or under the ideal internal enclosure volume and they’ll still sound pretty darn good.
For this exercise I’m going to install three of 10-inch subwoofers into the cargo area of my Nissan Murano, which is effectively a big hatchback. All the materials for this project will cost around $150 and will take you around six hours to complete.
List of tools:
- Tape measure
- Note pad
- 18mm MDF
- Wood glue
- Circular saw
- Cordless drill & wood bits
- Wood screws
- Trim glue
- Speaker wire
- Wire cutters
- Stanley knife & scissors
- Terminal cup
Step 1: Measuring the area
Measure the maximum width, height and depth of the area the box will sit and this includes the different top and bottom depths that will be required to allow a sloping front baffle to nestle neatly up against the rear seat. Make sure the main baffle has enough height to fit your chosen subwoofer, and ideally they’ll be facing rearwards to take advantage of bass loading into the cabin.
Step 2: Designing the enclosure on paper
Sketch out the enclosure in 3D and add in your dimensions. After subtracting the width of the MDF for each side wall (3.6cm for 18mm thick MDF) you can multiply height by width by average depth (top and bottom depths added, then divided by 2) to arrive at the internal volume in cubic centimeters. Divide the result by 1000 to get litres. To vary the enclosure volume reduce or increase one dimension and then recalculate to arrive at the desired internal volume, which will be suggested on the owner’s manual of your subwoofer. This gives you a list of MDF boards to cut.
Step 3: Cutting the first pieces of MDF
Mark out the rear vertical wall at the full enclosure height and cut the MDF using a circular saw. This will give you the straightest edge possible to allow a flusher finish when screwing it together. Measure out the bottom wall minus double the wall thickness (36mm for 18mm MDF). Using the angle setting on the circular saw cut out the MDF to create the angled front edge, leaving the rear edge to be at right angles to match the rear wall. Now that the remaining MDF sheet has an angled front measure out the appropriate top baffle width and cut its end at right angles.
Step 4: Initial construction
These three pieces should be assembled prior to the next wall being cut. Pre-drill the rear baffle with holes large enough for the self tapping screws to pass through, and smaller pilot holes into the walls they’ll bite into, as this clamps the walls tightly together. During final assembly of any wall apply a line of wood glue to the connecting surfaces.
Step 5: Marking out the side walls
Lay the enclosure on its end and mark out the two side walls. Once they are cut out attach them to the sides but add a small 5mm recess to each side, as this allows for neater trimming later and easier loading of the box. This minimal volume decrease won’t matter to the sound at all.
Step 6: Marking out the front baffle
Lay the construction against the next sheet of MDF and mark out the next cut with a pencil. Also mark the angle required for both cuts to arrive at a flush finish for the front baffle when it’s attached to the box. Cut this wall using the jigsaw on the correct angle setting. For this cut a jigsaw will be easier to work with than the circular saw.
Step 7: Attaching the front baffle
When drilling the pilot holes for this baffle you will need to drill at an angle to suit the way the baffle faces onto the side walls. Apply a bead of wood glue around the edge of the box and glue and screw this wall into place.
Step 8: Cutting out the subwoofer holes
Draw a vertical line through the centre of the wall the woofers and going to be mounted in and use the tape measure to work out the spacing for each subwoofer hole. Using the supplied template that came with your subwoofer, mark the mounting holes for each driver, pilot drill a large hole with your drill and then cut the holes out using a jigsaw.
Step 9: Terminal cup & sealing
If you’re using a terminal cup cut the hole for it prior to trimming. Once done run a bead of glue around every inner edge to seal up any air gaps to create a nicely sealed chamber.
Step 10: Cutting end wall carpet
Lay carpet into the end walls and use the Stanley knife and scissors to cut out the exact shapes of carpet for each end. These will be glued into place once the rest of the enclosure has been carpeted.
Step 11: Trimming the enclosure
Roll out your length of un-backed carpet and place the enclosure onto one end. Apply an even coat of adhesive glue using a brush to the front wall as well as to roughly the same area on the back side of the carpet that will be stuck to this wall. After allowing a few minutes for the glue to go tacky roll the box over so the glued face meets the glued carpet. Repeat this step for three all three sides of the enclosure except for the bottom facing wall.
Step 12: Cutting the carpet for the bottom panel
To create a flush fit for the two ends of carpet begin by trimming one end so that it creates a neat edge across the centre of the bottom of the enclosure. Lay the opposite end over the top and feel for where they meet together, cutting the opposite side with scissors along the same position.
Step 13: Gluing the bottom carpet
Apply an even layer of glue to both the enclosure and the back of each side of the carpet. After the glue has become tacky lay down one side neatly and try and create a smooth edge. The carpet will stretch easily so lining up the opposite edge should be easy. Trim any excess carpet off to create a seamless finish.
Step 14: Trimming the edges
Cut off any excess carpet to leave about three centimeters of overlap on each end. Apply glue to the ends of the main walls and about two centimeters around the side wall face edges, as well as to the adjacent areas of carpet around the circumference. Once tacky roll the carpet over and stick it down all the way around, trimming off excess carpet with the Stanley knife as you work around.
Step 15: Gluing down the side panel carpet
Now apply glue to the side baffles being careful around the edges to not get it on the carpet. Apply glue to the back sides of the ends you cut out previously and stick these into place. Connect the speaker wires to the terminal cup and screw this into its hole.
Step 16: Wiring and mounting the subwoofers
Connect the speaker wires to the terminals on the subwoofer, and if using multiple voice coils double check the wiring scheme to ensure you have the correct final impedance load. After pilot drilling the mounting holes screw each subwoofer into place using all available screw holes for a tight seal.
Your new subwoofer enclosure is ready to go!