Small Boombox for Less Than 80 Dollars That Packs a Punch

I've wanted to build a small boombox that was lightweight, easy to transport, and has decent sound (both volume and quality). There are MANY different designs out there for a DIY boombox, both small and large ones, and different diffulties from complete novice to expert level knowledge of electronics. This design is VERY simple, and requires only a minimum of skills and knowledge.

I based my design on a 2*20W tripath amplifier from "indeed hi-fi". It plays plenty loud for a beachparty or BBQ with your friends and will easily play for a 3-day weekend. The entire system weighs about 6-8 pounds (i think...EDIT: it weighs 13 pounds) and the picture shows it with a soda can for size reference.

There is also a sketchup model of the design attached.

You need:

• No actual skill or experience building speaker systems
• Basic carpentry skills, so the box will not be crazy crooked :P
• basic tools (Jigsaw, a drill and a pensil...yes that's really all the tools needed)

Materials

1. 12mm plywood for the box
2. Amplifier that runs 12V DC
3. Speakers
4. 12V battery 4.5Ah capacity
5. DC powerjack to connect battery to amplifier
6. Handle for carrying
7. Cable to connect amplifier to phone or mp3
8. LM7805 voltage regulator (OPTIONAL)
9. Bluetooth module (OPTIONAL)
10. 3-pin SPDT ON-ON switch (OPTIONAL)
11. Terminal for connecting the charger from the outside (OPTIONAL)

EDIT #1:

I have added four different wiring diagrams for the boombox.

1. The minimum circuit, with only amplifier, battery, cross-overs and speakers
2. + added circuit for connecting charger without opening the box or frying the amp
3. + simple bluetooth wiring
4. + more advanced bloetooth wiring

Circuit 1 and 2 don't necessarily need any soledering, but circuit 3 and 4 will need a bit of soldering (not much though).

EDIT #2:

Thanks for the attention of my first instructable :D af
hope these help a little, and feel free to ask questions :)

Small boombox.skp
Download

Step 1: Choose Your Parts

The most crucial parts, when building a boombox, are amplifier, powersource and speakers.

If you don't want to read all this text (it's mostly just explaining HOW to pick your parts), jump to the bottom of the page, where i've made a suggested parts list :)

Amplifier

As i mentioned in the intro, i based my design on a 2*20W tripath amplifier from "Indeed Hi-Fi", because i had it from another project i made a while back. It outputs 2*20W RMS with a 4ohm load. This type of amplifier is great for these kinds of projects, because a lot of them run on anything from 9-24V.

NB!! not all amps do this, so check to make sure.

My amplifier in particular runs on anything from 9-14V, which is great, since i plan to run it from a 12V battery.

You can of course choose any type of amp you would like, however i recommend to stay away from car amplifiers as they are not very powerefficient, since their normal environment has an endless powersupply (the cars engine).

Powersource

Selecting your type of powersource is vital (of course :P). Most amplifiers can be run of batteries, or you can power them with a powersupply.

I went with a 12V sealed lead-acid battery with a capacity of 4.5Ah. It is a fairly small capacity, but a battery's size and weight increase as the capacity increases. So to keep the weight down, not take up too much space in the box and keep the cost down, i chose this type of battery.

Again, you can choose whichever method you want, but i would recommend to power it from a battery so you keep the mobility of the boombox :)

Speakers

The type of speakers are paramount for sound quality and volume the system will be able to output. You can buy predesigned 2-way system which comes with a premade crossover designed for the speakers.

This kind of speaker sysmtem is composed of a mid-woofer (makes the bass and middle tones) and a tweeter(makes the treble tones). when picking speakers, check to make sure they have a frequency response that goes as low as possible! (remember the human ear can only detect between 20Hz and 20000Hz). Choose a set that goes as low as possible, but 50Hz should be just fine.

When it comes to bass in speakers, bigger is sometimes better :D I recommend you choose a set with a 5.5 inch or 6.5 inch woofer, as the deep bass frequencies tend to get clearer as the speakers gets bigger.

The last thing you want to know about speakers, is that sensitivity(also called SPL) plays a HUGE role in how loud they can play. the higher the sensitivity, the louder they can play. So to make it short, find a set with a sensitivity of minimum 91dB

These system range from very cheap (and mostly crappy) to really really expensive. Find your budget and pick a set you like :)

Speakers: http://www.parts-express.com/boss-pc652c-phantom-6...

Battery: http://www.parts-express.com/power-sonic-ps-1250f2...

total cost of electronics: 73.45 dollars + shipping

These are the bare minimum of parts you need to make it work. You could add a bluetooth module for wireless music, but it gets a bit more advanced, and you need to solder, if you want it done cheap. So for now i will keep it as simple as possible and keep it to the basics.

Step 2: Building the Box to Match the Boom

Building a speakerbox is not just slapping a few pieces of wood together to make a box for mounting the speakers in...or is it?

NO!!! NO!!! NO!!!...is the answer, if you want to make a high-end hi-fi system. That requires experience, many calculations, simulations and lots of measuring.

Well...we're not going to build a high-end hi-fi system :D That doesn't mean that the design of the box is of no importance, but for us it's more of a "form follows function"-thing. We want a portable boombox, so it cannot be too big, but we still need to fit all of our electronics in it, so there has to be some room inside the box.

I build my box from 12mm plywood, and this is what i recommend. You could use thinner wood, but if you choose to use thinner wood, i recommend using bracers in every corner of the box.

the box:

2 pcs. 580mm x 212mm (front/back panel)

2 pcs. 580mm x 150mm (top/bottom panel)

2 pcs. 126mm x 212mm (end panels)

that's all you need for the box, these six panels make up the box. this will give you a box of roughly 14 liters. You can make the cutouts for the speakers as you like, but i recommend placing the woofers to the sides and the tweeters towards the middle, as this gives the best weight-distrobution for carrying the box, and it is much easier to stuff everything in there.

It is important that the box is as airtight as possible, because if the air escapes from inside the box, the sound quality is going to suck. So i recommend sealing the box with woodglue as you assemble it.

How to assemble

Cut the different pieces
Cut holes for speakers, amp, and anything else you might need a hole for (switches, minijack cables for music etc.)
Paint all the panels (if you want to)¨
Assemble front panel on top of bottom panel. (see picture above)
Assemble both side panels on top of bottom panel (see picture above)
Don't assemble back or top panel just yet, you want to install the speakers and amplifier first (next page)
After you have assembled all of the electronics, put the back panel on the box
I suggest you mount the top panel with hinges, so access to the electronics is easy.

Step 3: Connecting the Electronics

How to:

Mount the speakers in the holes
Mount amplifier
connect speakers to amplifier
connect battery to amplifier

These 2-component speaker systems usually comes with a diagram for assembly, so just follow that :) the wiring diagram shown on the picture above is generic diagram, and may not apply to your exact speaker choice (but it probably will), Check to make sure

for connecting the battery to the amplifier, you will need a DC powerjack, they can be bought here: http://www.aliexpress.com/item/10pcs-lot-Male-DC-P...

"+" connects to the red terminal on the battery

"-" connects to the blac/blue terminal on the battery

that is it...

turn it on and bask in your glory! :D

EDIT:

If you want to add Bluetooth or terminal for external charger, i've added circuit diagrams for these as well :)

Step 4: Future Add-ons

There is loads of room for improvement in this design. I've already added bluetooth for wireless music, but i'm thinking of adding a solar panel for even better battery-life, and LED's that blink to the beat of the music. I'm also planning to add a shoulder-strap, so i can take the boombox along with me when i travel by bike.

I did add a tone-control circuit, because the amp i have in my system does not have one (the amp i linked to in suggested parts has one built in).

if i wanted to spend some more money, i could've gone with a li-po batterypack in stead of lead acid, to save some weight. I could put a better amplifier, but again, my focus was also to keep the price of it down.

EDIT:

I added a digital batterymeter, i bought it for about 10 dollars from china. i think it makes a nice addition to the design, and looks pretty cool :)

I also got the external charger circuit connected so i can seal the box properly and still charge the battery.