Speaker Building

Here are a few tips for building a subwoofer with the following features:

My preferred arrangement of panels

I build my speaker boxes out of 18mm MDF, with ports of PVC pipe, and finish with either veneer, or rounded edges and three coats of polyurethane.

The front panel is double thickness, comprising an outer layer which has no visible seams and an inner layer that is fully surrounded by the box

The top panel has a seam to the front, and the side panels have seams to the top and front.

The rear panel is fully surrounded by the box

The bottom panel is surrounded by the outer front and sides, but visible at the back

Tips for cutting rectangular panels

Check that your new sheet of MDF is square, and if so, mark each corner. This gives you a good corner and 2 good edges to start with and you will be able to identify the good parts of the offcuts for later use. Mark the other 2 edges 5mm oversize and cut with your power saw.

If an edge is not going to be visible ( butts up to another panel), it will need to be trimmed to the exact dimension. This can be done with a router using a straight bit and a fence clamped as a guide. You will get a more accurate dimension and a much straighter edge using this method

If an edge is to be visible, it can be "left hanging", and after gluing can be cleaned up with the router using a flush trim bit.

Construction walk-through

Read all steps before beginning work - Particularly the note about router height on Day5.

Day1

I use PVA glue, which takes 24hrs to reach full strength. This generally means working alternate days. (Day1 - cut route etc. and glue. Day2 - Drying not done till afternoon. Day3 repeat)

Cut the following panels:

Front inner panels and rear panel - good corner top left - all edges exact

Side panels- good corner top-front and leave back and bottom edges oversize

Top panel - good corner not required, (use offcut if possible) - front edge true, sides and rear edge all oversize

Bottom panel - Good corner to front. Sides exact and rear edge oversize

Front outer panel - will be trimmed all round later so no need for a good corner or edge at this stage. Cut 10mm oversize

Also cut some strips to be used for edge bracing. Make them the same width as the sheet is thick (square cross-section). You will end up with 2 good faces and 2 ordinary faces - no need to trim with router as glue will fill the gaps.

If you have access to some large clamps, you can glue these panels as shown here. (Viewed from bottom)

As you can see, the clamps hold the top down, and the twisted rope holds the sides in at the bottom.

The front inner panel, (not visible here), fully enclosed and sitting flat on the table, is used as a guide and not glued at this stage.

Some sandwich plastic between the front and side panels will stop glue getting onto the front panel

Sitting on a flat surface with the front of the box down (all good edges) ensures everything will dry true. Here, I sit it on the front outer panel (not glued)

An offcut with a good corner was used to get all the seams square as the clamps were applied.

Allow to dry for 24hrs

Day3

Tap out the front inner panel to make sure it isn't glued from the previous work.

Re-insert front panel but do not glue. Lay face down as before. Glue edge bracing for the top-side seams and the bottom-side seams. Clamp rear end of bracing. Stand box up and remove front inner panel. Clamp front end of bracing. (8 clamps required)

Glue front inner and front outer panels together, clamping well - leave 24hrs (Another 6 clamps required, or an extra day. Alternatively park small car or large motorcycle on top....just kidding, a stack of house bricks will do!)

Day5

Use a router and flush-trim bit to clean up the sides of the top panel and the bottoms of the side panels

Front panel - cut rebated speaker hole and port holes using plunge router and circle jig.

Quick Tip - When cutting out circles, put 2 screws through the panel inside the area to be cut out, and clamp the rest. This will stop any movement when you cut that last little piece out - otherwise you will damage your panel. The screws need to be long enough to go into the work surface under the panel. I have a work table with a chipboard top that I can screw into and route into to my heart's content. When it gets too chewed up, I just replace it.

For the driver cutout, do the larger diameter first and then the smaller. Depending on the plunge capacity of your router, you may have to turn the panel over to complete the cut.

For the port, plunge route a cylindrical cut the exact diameter of the port and to a depth of just over half the panel thickness. This will allow the port to bridge both sections of the double layer front panel. Route a smaller hole right through from the front. Make this 10mm smaller diameter than the port's internal diameter, as it will be cleaned up later with a flush-trim bit and then a rollover bit.

If required, drill LED indicator hole and route rebate.

If you are using shelf bracing, cut out brace and route pattern through centre. Route rollovers on cutouts to improve airflow. If you leave the front edge until last, it will be easier to clamp this panel while you do all the fiddly stuff.

The pattern to use for the shelf brace is up to you. I like to have a cross-strut as shown here. I make the width of the strut the same as the thickness, giving a square section. The material around the perimeter I make 5mm wider to allow for what is rebated into the box itself. At the back of the bace, make some cutouts to clear the edge bracing that will be fitted to the side-back panel seams on Day7

If using 18mm thick MDF, you would end up with something like this:

Shelf brace

Route slots in cabinet sides. Don't cut slots all the way to the back. Stop short enough to leave room for the edge bracing to be fitted to the rear-side seams. If you go right through, the slot will be visible from the back of your speaker. If you are using the cut list generated by boxnotes, the slots for the shelf brace need to be 5mm deep

Route slot in back of front panel for shelf brace.

Quick Tip - You can slide the front panel into position, and reaching in from the back, use the slots cut in the side panels as guides to mark the exact position for the slot in the front panel

Route slot in front of back panel for shelf brace. Don't cut slots all the way to the sides. Stop short enough to leave room for the edge bracing to be fitted to the rear-side seams. Whilst the slot would not be visible if you don't stop short, doing so maximises the surface area for the glue.

Quick Tip - You can slide the shelf brace into position, and reaching in from the front, use the slots cut in the side panels as guides to mark the exact position for the slot in the rear panel

Have a quick look at the Snorky Gallery and the EBS-Snorky Gallery if you are unsure about how the shelf brace fits.

Glue port stub to front panel

Glue shelf brace into front panel only. The shelf brace / front panel assembly can now be slid ito the the box to hold the brace in the correct position. This shot shows how it fits. Take care not to end up with anything glued to the side panels. Some sandwich plastic between the front and side panels can help

Lay the box face down and allow to dry for 24 hours.

Day6

Make extra panel to allow Amp rebate if desired.

Route cutout in rear panel and trim with a 45degree bit or rollover bit to facilitate airflow across amplifier.

Glue and clamp extra panel to rear panel

Day7

Route port edge with rollover bit. This gives a smooth port flare, is free, and looks great!

See the Routed Port Flares page if you need more detail on this step

Remove front panel / shelf brace assembly

Glue remaining port pieces with plumbers glue or quick setting epoxy. Use masking tape to prevent excess glue finding its way onto the inside surfaces of the port.

If ports pass through shelf brace, a generous application of hot melt glue can be used to stabilise the ports to the brace

Glue back panel and edge bracing for the side-back panel seams into enclosure. Lay enclosure on its back, on blocks so that the back panel caries the weight. If you have a large clamp, use it from underneath, to hold the sides in tight against the back panel

Day9

Flush trim around rear panel

Sand interior of ports to remove any excess glue and sharp edges

Glue in foam damping sheet to top and bottom panel if required. This helps if top-bottom dimension is large enough for standing wave to be a problem.

For subwoofers, this is only required if enclosure is tall. For example a 1m tall enclosure will have a top-to-bottom standing wave of 178hz With the driver centre 300mm down from the top, the driver-to-bottom standing wave wave will be 126hz) See Boxnotes for calculating your own - it will also calculate the dimensions of each panel and can print your cutting list

If you have used PVA glue (Aquadhere or Titebond II) you should apply some Neutral cure Silicone to seal all available internal seams. Don't use normal silicone, because as it dries, it emits acetic acid, which can damage your electronics and drivers. This step is not required if you've used Polyurethane glue (Aquadhere Durabond or Gorilla glue) because it expands as it cures, sealing any gaps.

Glue in shelf brace / front panel assembly. Clamp or weight well

Day11

Flush trim front panel

Rollover trim all external edges (unless you are going to use veneer)

Sand all over ready for applying your selected finish

Silicone front panel internal seams