This is my version of a boombox that will pretty much blow your brains out :P It is based on the "boominator" by Saturnus (opensource), so all the credit really goes to him! :) I have deviated a little from his original design for the box, but the interior of the speakers housing is pretty much the same, so quality of sound should be maintained. I have added a larger compartment for electronics, so i could fit larger batteries, as i have also put a much larger amplifier in it.

Anyway, this should be a fairly thorough walk-through on how to make this. Sorry there are no actual pictures of the system, but i sold it, and i did not plan on making it an instructable at first.

It is a rather large build, and basic woodworking skills are needed, or the box is not going to look very good. If you are not used to working with powertools, get someone to help you. The electronics are very basic, and anyone should be able to assemble it.

It is heavy as hell, so i definately recommend putting it on weels.

Lets get started! :)

Step 1: Speakers, Amp and All the Other Goods That Go Inside!

I will not go in to great detail on how to wire everything, as i belive that the wiring diagram is a much better way of understanding it. I will rather focus on why certain parts are needed, some are just nice to have and why i made some of the choices that i have made.

The wiring is very basic, but feel free to ask questions if something is unclear.

Solar power and batteries

When connecting solar panels to your battery, it is always a good idea to use a charge controller. This ensures that you will not overcharge your batteries, as this will shorten their lifespan much faster, effectively ruining your batteries. since we are connecting 20W (2x10W=20W) solar panels to the batteries, we will definately need a charge controller to make sure we dont overcharge them.

Batteries: series or parallel?

The amplifier used in this build, will run on anything from 10V to 32V, so i could choose to either wire the two batteries in parallel or in series. But what is the difference?

Parallel

Wiring batteries in parallel will increase the capacity (AH) but keep the voltage the same. So with the two 12V 26AH batteries chosen for this build i would get a total capacity of 52AH (26AH+26AH=52AH) and a voltage of 12V.

This is done by connecting the positive terminal on Battery 1 to the positive of Battery 2, and then on to the amplifier. Likewise with the negative terminals.

Series

Wiring batteries in series will increase the voltage, but keep the capacity the same.This means that the two 12V 26AH batteries i have would still have a total capacity of 26AH, but a voltage of 24V.

This is done by connecting the positive terminal of battery 1 to the amplifier, the negative terminal of battery 1 to the positive terminal on battery 2, and then the negative terminal of battery 2 to the amplifier.

This is exactly the same with the solar panels, except instead of AH (Amp Hours) its just A (Amps).

I wired the batteries in series, because i wanted the higher voltage. I wanted this for two reasons.

It gets better efficiency with the amplifier i picked (this means longer play time, i want that)
It gives a higher output (i definately wanted that! :P)

Speakers: series or parallel?

When wiring speakers to the amplifier, the main thing to keep in mind, is the equivalent impedance of the speakers connected. There are two ways to wire the speakers to the amplifier: Series og parallel (yes, exactly like the batteries.)

Parallel

When you connect two speakers, of equal impedance, in parallel, the equivalent impedance, is half that of a single speaker. We have two 8ohm speakers(2 left and 2 right), so when they are wired in parallel, the equivalent impedans is only 4ohm. If you wired three speakers, of equal impedance, in parallel, the equivalent impedance would only be a third that of a single speaker, which is 2.6ohm, and so on.

Series

When wiring speakers in series, you just add the impedans of each speaker. So the two speakers, for either channel, would have the equivalent impedance of 16ohm (8ohm + 8ohm = 16ohm).

A few handy rules when determining wether to wire your speakers in series or parallel:

Higher impedance = high efficiency, low output
Lower impedance = low efficiency, high output
Never go lower than the rated impedance of the amplifier, going higher is OK

I went with a parallel solution, so i would get as high an output as possible.

Notice the resistors that are installed right before each tweeter on the diagram. These are there to dampen the tweeters, otherwise they would be too dominant.

Amplifier

The amplifier i picked for this build, is a 2 x 100W 2-channel stereo amplifier @4ohm, 24V. This means, that when a speaker (or a set of speakers), with an equivalent impedance of 4ohm, is wired to it, it has a maximum continuous output of 100W per channel, a total of 200W, when powered by a 24V source. Paired with speakers that have high sensitivity, this can play incredibly loud! This particular amplifier has fairly good efficiency, at 86% with a 4ohm load.

If you wired speakers with an equivalent impedance of 8ohm, you would get about 90% efficiency from the amp, but only a maximum continuous output of 60W per channel, a total of 120W.

This amplififer need active cooling so it does not overheat. It comes with a small fan mounted on it, but if you put it in a sealed compartment, the air will heat up, and the cooling might not be sufficient. I solved this by making small holes in the top and bottom so the air is circulated passively.

TL;DR
I wired the batteries in series and the speakers in parallel, because this gives the highest output.

Step 2: Build the Cabinet and Install the Electronics, a Step-by-step Guide

Cut all the different panels that are needed to build the kabinet. I have given the different panels letters, so it is easier to describe the assembly process. The cabinet is made form 12mm plywood.

• 2 pcs A - 772mm x 276mm (Bottom/Top)
• 2 pcs B - 796mm x 417mm (Fronts)

• B1 - 300mm x 417mm
• B2 - 300mm x 417mm
• B3 - 196mm x 417mm

• 2 pcs C - 276mm x 417mm (Sides)
• 4 pcs D - 393mm x 276mm (Speaker bracers)

• 1 pcs E - 196mm x 276mm (Electronics compartment bottom)
• 2 pcs F - 180mm x 70mm (Handle/bass reflex 1)
• 2 pcs G - 160mm x 50mm (Handle/bass reflex 2)
• 2 pcs H - 393mm x 276mm (compartment sides)

The big hole down the middle of panel B (named B3 later) in the sketchup file is ment to be a door, so electronics can be accessed once the build is complete.

NOTE: All joints should be sealed. I used wood glue for this.

1. Cut on of the B panels in to three sections B1, B2 and B3.
2. Cut holes for the woofers and tweeters in B, B1 and B2, as showed in the sketcup file.
3. Cut holes in C, F and G as shown in the sketchup file. These hole make handles/bass reflex and are vital to the design.
4. Glue panel C, F and G together(one of each, for each side). Since they will not hold anything, screws should not be necessary.
5. Paint panels A, B and C. (optional, but i recommend it, so it keeps moisture out of the wood)
6. Cut holes in H and E panel for routing wires through. Preferably as small holes as possible, 15mm-20mm should be more than enough.
7. Mount woofers and tweeters in B, make sure to leave speaker terminals turning upwards. Seal the edges around the speakers and screws with acrylic sealant. Reinforce the tweeter with it aswell, this is done by adding some to the creases on the back of the tweeter.
8. Cut holes and cut-ins D panels, as shown in the shetchup file.
9. Assemble one A panel and B1 and B2, as shown in the shetchup file. Start with the A that will be the bottom.
10. Assemble both C and H panels to the part from step 9, as shown in the sketchup.
11. Mount the D panels, as shown in the sketcup file. NOTE: The D panels should be glued to the woofers when they get mounted. I used a two component epoxy glue for this.
12. Mount the B panel, and remember to glue the woofers to the D panels.
13. Mount E panel. The placement of of this panel is up to you, and how much room you need for the batteries. The batteries go below the panel.
14. Route wires to the speakers through the holes in each H panel, and connect them to the speakers according to the wiring diagram.
15. Route wires from the batteries through the hole in E panel and connect batteries.
16. Mount solar panels on the last A panel. Make sure to cut holes so you can route the wires from them internally.
17. Make sure your wires from speakers, batteries and solar panels are long enough to reach everything that needs to be connected.
18. Mount the last A panel.
19. Connect all electronics according to wiring diagram.
20. Seal wire routing holes in H panels, you can also do it in E panel, but it is not necessary. I used acrylic sealant here aswell.
21. Mount B3 panel with a pair of hinges and a locking mechanism.
22. DONE!

With glue that needs to set, paint that needs to dry and acrylic sealant that needs to harden, this takes more than a day to make.

The Finished product, is a (fairly) portable boomblaster, that can can play for an 8 day festival, without having to be charged by anything but the sun. It will beat most portable boomblaster as far volume goes, and rival most/all in quality of sound. It is a great little monster! :D

I have entered it in the littlebits tech contest, so if you like my work, give it a vote :)

Parts:

• 4 x HP10W Woofer (http://goo.gl/IFNf2O)
• 4 x MPT-001 Tweeter (http://goo.gl/C5I0rr)
• 2 x 12V 26AH SLA batteries (http://goo.gl/0EDykQ)
• 1 x 200W(2 x 100W) 24V amplifier (http://goo.gl/0r4uDA)
• 1 x ON/OFF Switch
• 1 x Tone control board w/ volume control (http://goo.gl/52bHcG)
• 1 x 24V charge controller
• 2 x 10W 12V solar panel
• 4 x 47ohm 2W resistor
• Plywood 12mm
• Speaker wire
• Wire (for batteries)
• Fuse + fuseholder

Tools:

• Jigsaw
• Drill
• Circular saw
• Hole saw