Introduction: 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 :)

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 :)

Suggested parts

Amplifier:http://www.aliexpress.com/item/Handover-Hi-Fi-Car-...

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

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

Step 3: Connecting the Electronics

How to:

  1. Mount the speakers in the holes
  2. Mount amplifier
  3. connect speakers to amplifier
  4. 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.

Comments

author
M L G (author)2016-05-05

Hi, Great tut! thanks for sharing.
I'm new to this whole instructables thing but love to potter and tinker with electronics in my spare time albeit I have only just started doing this in earnest and still very much a complete novice. What I wanted to ask you was: would it not simplify the design in terms of the bluetooth if I just used this bluetooth module http://tinyurl.com/hgtwnrd
Its on ebay and is a class D amplifier which I believe is supposed to be pretty good right? Or there is this one which at least has knobs for manual operation again on ebay http://tinyurl.com/jxjqchx

author
JohanH5 (author)2015-10-12

Hey, great instructable! One question thou, if I read the wiring diagram correct, you cannot use the boombox while it's charging? Is there any way to change this, for example if you connect the ON/ON switch to get constant power from the carger, and then direct the current to either battery or the amp? Sorry confusable english ;)

author
Grisling (author)JohanH52015-10-12

You could remove the switch all together, it will charge and play just fine. I added the switch, because my charge terminal are a little exposed, so in order to be 100% sure they didn't short accidentally while not charging I added the switch so they're disconnected when not in use. You could also modify it slightly so the switch just connects/disconnects the chargend terminals without interfering with the power to the amplifier.

author
IsaiahK2 (author)2015-07-28

So it does not need to be plugged in to a wall outlet you can take em anywhere you go?

author
Grisling (author)IsaiahK22015-07-28

No it doesn't, it's powered by the battery when not plugged in to a wall outlet. So yeah, I can take it anywhere I want to, I've mostly used it at the beach.

author
ValdemarA (author)2015-03-17

I don't now if this thread is still alive but is it possible for an aplifier with a 15 w output to power at speaker at 100 w ?

author
Grisling (author)ValdemarA2015-03-17

yes of course. The 15W from the amplifier is the maximum power the amplifier can output. The 100W of the speaker is the maximum rated power it can handle without breaking. Since 15W is far less than 100W there is also no chance that the speaker will break even after hours at maximum volume from the amplifier.

author
ValdemarA (author)Grisling2015-03-19

But will it be able to deliver enough power to the speaker when there is such a difference? Or does it even matter?

author
Grisling (author)ValdemarA2015-03-19

yes, no problem. What matters in this case is the impedance of the speaker, most amplifiers can handle 4-8 ohm per channel, and that's also the most common speakers. Your 15W amplifier will play just fine in to a 1000W speaker if you wanted to do that.

author
ValdemarA (author)Grisling2015-03-19

Okay, thank you very much!! This is really helpful! Really awesome build btw!

author
BAURO (author)2015-01-27

how do you charge the battery?

author
Grisling (author)BAURO2015-01-28

i have installed an old speaker terminal in the back with two brass connectors that i hooked up to the battery with a switch, so that i can connect an external lead acid charger to it, and still disconnect them so you don't accidentally short the battery. i didn't have those parts at the time i made the instructable, and i forgot to add pictures.

author
dillonxti (author)2014-09-26

Can buy the parts for this at Parts Express

author
Grisling (author)dillonxti2014-09-27

yes you can :)

author
michael.kudla.3 (author)2014-09-08

Any chance you can save it in an older format? 2013 say?

author
SeanR1 (author)2014-09-01

How would I go about adding 2 microphone ports to this so that I can make one for my girls to use for sing-alongs?

author
DUDE123456789 (author)2014-08-19

How much cheaper isit to make it yourself than buy from store?

author
Grisling (author)DUDE1234567892014-08-21

well, where i live, most boomblasters available in stores cost around 110-120$, so its not that much cheaper. I did it mostly for fun.

author
DUDE123456789 (author)Grisling2014-08-22

thanks

author
michaelgc (author)2014-08-12

nice, looking for fun technology projects for my middle school stem kids.

author
Cool Dude 123 (author)2014-08-12

Ill pay 200

author
Grisling (author)Cool Dude 1232014-08-12

Thanks for the offer, it's not for sale though :)

author
Grisling (author)Cool Dude 1232014-08-12

Thanks for the offer, it's not for sale though :)

author
Ethereo (author)2014-08-11

I have a big question, I have 3 speakers, (2 mid range & 1 small subwoofer), and i dont know how to make the enclosure, i've read lots about the pros and cons of the sealed box and the ventilated box, and i can't decide which one to use.

author
Grisling (author)Ethereo2014-08-12

Hi, I would seperate the the woofer from the two mids (and maybe the mids in two seperate chambers, they don't need to be ported). As for choosing a sealed or ported enclosure, remember that the ported enclosures as a rule of thumb are bigger than the sealed ones, so take that in to consideration.

If you have any specs on the speakers you can also calculate the EBP (Efficiency Bandwidth Product) to see if the woofer would work best in a sealed or ported enclosure. EBP = Fs/Qes. If the EBP is greater than 90 its best in a ported, and below 50 its best in a sealed. Between 50-90 it's what you would prefer really (again just a handy rule of thumb).

Hope this helps :)

author
BigStoddy (author)2014-08-11

Well Done! I'm an electronics beginner but you've given me hope. Next addition... cup holders where the can sits in picture #1. :-)

author
Grisling (author)BigStoddy2014-08-11

I didn't even think of that, what a sweet idea! :D

author
LeonardoR1 (author)2014-08-10

It is beautiful

author
Grisling (author)LeonardoR12014-08-10

Thank you very much! :D

author
LeonardoR1 (author)Grisling2014-08-10

You know,I'm dancer and I need a small boombox to show in the street,your design is nice ,I like it.

author
barobbin (author)2014-08-06

Do you get any distortion? Does the amp push those speakers ok? Also could you post some pictures of the bluetooth setup?

author
Grisling (author)barobbin2014-08-10

Hi again, i have finally uploadet pictures of my bluetooth setup :)

what you're seeing, is probably the easiest way of connecting with bluetooth. I used a USB bluetooth dongle, a 3*1.5V battery holder, a usb extension cable and an on/off switch. I run the bluetooth seperately from the 12V powersupply, because i didn't have a LM7805 voltage regulator while building it. I cut the USB extension cable and used the black and red wire inside of it to wire it to the battery box. I soldered the red (positive) wire to the battery box via a seperate switch so that i can turn it on and off, and the black (negative) wire directly to the box. the bluetooth module came with a minijack output so i just connect it directly to my amplifier.

IMG_20140810_144340.jpg
author
Grisling (author)barobbin2014-08-06

Hi, no i don't have any distortion in my setup, but this really comes down to the amplifier used in the setup. The better (and often more expensive) the amp, the better the sound quality. The amp i linked in the suggested parts list is a decent amp, with a little less power than the one i have used. the amp will drive the speakers just fine. I don't have any pictures of the bluetooth setup right now, but i will post some ASAP :)

author
static (author)2014-08-09

A good instructable for those who are clueless as to now to go about constructing boom box. True when constructing a speaker enclosure you would want to insure the joints are sealed. With no isolation of the woofers it may be better if the case4 had 'ventilation", this not like speaker install on a cars' package shelf and of the volume of the trunk to the rear of the speaker cones. As you indicate you weren't going for HiFi but loud. No to go figure out why the Firefox spellcheker isn't fully funcying with thi comment field.

author
magnuswf (author)2014-08-08

Og forresten, hvad hedder din amp, og hvor har du købt den?

author
Grisling (author)magnuswf2014-08-09

Det er en TA2020s fra "Indeed Hifi". Jeg købte den for lang tid siden hos canopysound.dk da jeg skulle bygge en boominator til festivaller. Du kan også finde dem på ebay.

author
magnuswf (author)Grisling2014-08-09

Fedt, tak :)

author
hamsammy (author)2014-08-07

Nice looking boombox. Simple and effective. I've done a number of simple builds like this and they're always fun.

Just one note I would add. The efficiency of a speaker is not a tell for how loud the speaker can be, but rather how loud it is given a standard unit of input (2.83V typically). So a speaker with a higher efficiency will play louder than one with lower efficiency in that test but this doesn't not mean the speaker with the lower efficiency can't get louder than the other; that's a matter of power input and handling.

author
Grisling (author)hamsammy2014-08-08

Hi, as i understand it, if you give two different speakers the exact same signal, the one with the higher sensitivity will be loudest?

author
sesparza1 (author)2014-08-07

Heyyyy its great congratulations

author
GrfxGawd (author)2014-08-07

I see you're aware of the volume of the enclosure issue and chose a sealed design, one change will radically help with stereo separation and imaging. Move the tweeters to the upper corners. With the high frequency drivers so close together it's possible to experience a lot of problems with cancellation. It also wouldn't be a poor choice to place an internal baffle to separate the two mid/bass drivers. You can stuff a fair amount of household type insulation into each side and effectively "fake" some additional volume (as in space). It'll also help reduce any unwanted resonant frequencies and reflections from the cabinet walls. If you'd like the additional efficiency of a ported box, you could passively radiate and weight the passive radiators to add dampening to help compensate for the small internal space. Or you can fill a conventional port with soda straws, sounds goofy but it can be an effective fix for porting an enclosure that's effectively too small. Slot loading the ports is yet another potentially useful consideration for space compromised enclosures. Considering the design and application, having a bit of a peak around 50hz wouldn't really be a bad thing. Awesome job of supplying detailed information about your project!

author
Grisling (author)GrfxGawd2014-08-07

Hi, yes my tweeter placement was chosen for looks, but i haven't had really had major problems with frequency cancellation(it sounds pretty good, havent measured anything because i don't have the equipment at home and my school is closed for the summer). I didn't think about the insulation, which might be a good addition.

I didn't seperate the boombox in to two seperate chambers because i was a bit lazy when designing it, and didn't bother :)

Thanks for the advice on the ported possibilities, never heard the one with the straws though :)

GREAT feedback, thanks a lot! :D

author
wobbler (author)Grisling2014-08-07

Good instructable and good loking finished design.

Regarding the above comments, because the two tweeters are being driven by different signals
(left/right) phase cancellation isn't really an issue. Phase
cancellation is important when both tweeters are driven by the same
signal in a mono system. Similarly, separating them won't have any great
effect on stereo separation . This design won't really have any
stereo separation to speak of anyway unless you have your head about a
foot in front of it.. From further away there will be none. You could
try to create some stereo separation by angling the tweeters outwards
and try to bounce the signals of walls, but given that this is designed
to be portable and used outdoors it probably wouldn't work. In
reality, sonically at any distance beyond a couple of feet, boomboxes like this are effectively mono systems.

Adding some
speaker wadding though is a good idea and should make the speaker sound better.
However, if you do add speaker damping material, make sure it is not
allowed to cover up the electronics. It will act as an insulator and
either cause the electronics to overheat or may even catch fire (this
happened to me with a subwoofer I made with internal amp like this and
the wadding caught on fire). Even without speaker damping material, my only other worry about this design is
that the electronics are inside the sealed enclosure and there is no
ventilation, so potentially it could get warm in there anyway. However, it appears not an issue here as your design seems to be working ok.

Similarly, as we go lower in frequency from the mid-ranges, because the bass in a signal is effectively mono, putting an internal baffle between the woofers may not actually have any effect or be needed and could actually make the bass worse by making each bass speaker be in effectively its own smaller enclosure. That's why you only need one subwoofer in a stereo system,

You might also find that it sounds just as good driven in mono, which would make for an interesting experiment. Do we really need two amps and stereo speakers in a boombox other than for visuals and expectations?.

author
GrfxGawd (author)wobbler2014-08-07

I respectfully disagree about tweeter location, the impact of phase cancellation and no benefit in creating enhanced stereo imaging (in both tweeter placement, and dividing the cabinet), but agree about potential issues of overheated electronics (especially the battery). I further acknowledge that halving the currently shared space will greatly increase the effective Q per the design, hence my suggested methods to help mitigate that potentially unfortunate result.

I concur the cabinet dimensions substantially limit the soundstage yet I assert the application of my suggestions should help achieve better coherence, more spatial information and tighter, clearer bass with less distortion - static (THD, IM) and especially dynamic (TIM, TID, SID, etc).

Every true audiophile understands that a "mono subwoofer" for anything above 38 hz and exclusively for the sole purpose of enhancing special effects is pure heresy and the unholy spawn of Satan...

I will not argue the well known effects of acoustic coupling and why a "mono subwoofer" can potentially be effectively employed in a multi-driver installation - this is intended primarily for open spaces, not enclosed.

"Subwoofers" indeed... *shudders*

Next I expect you'll advise he simply slap a single 5X7 driver into a box and call it good. ;)

In all seriousness, mainly I just wanted to provide motivation for him to further investigate the design and construction of speaker cabinets. I feel deeply rewarded by the application of what knowledge I've been able to acquire and apply.

author
GrfxGawd (author)Grisling2014-08-07

PS. This was my first definitive source. Out of print, but nothing contained will be outdated. All the principles of acoustics still apply. http://www.amazon.com/Building-Speaker-Systems-2nd-Edition/dp/B000THVC3S

author
GrfxGawd (author)Grisling2014-08-07

You're kind of where I was in my late high school years. If anything I said helped, it brings me joy to share it.

author
jayeshshinai (author)2014-08-06

I need this for my camping trips. Can you give me an idea how long the battery lasts? Whats the method to calculate battery life (hours of music at max volume?).

Boomshankara.

author
Grisling (author)jayeshshinai2014-08-06

Well, the basic math of it (voltage*capacity; 12V*4.5Ah=54Wh) says about 1.5 hours at full blast. That's not true though, as i have run it for several hours at full blast without loosing power. I tested a similar system, with the exact same amp actually, but with a 7.2Ah battery, and it played for 6 days before dying (mixed listening volume during day, and 2 parties). So you should get at around half that with a 4.5Ah battery i think.

author

I've noticed the same...
I have a 12v 7ah battery, and a 100w amp. It played at near max power for over 8 hours

author
Grisling (author)jayeshshinai2014-08-06

alternativly just opt for a 7Ah battery, they are not much heavier, and you could fit in in the design as it is.

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