DIY boombox

[SavidSelim]

I would like to build a boombox out of an old typewriter case and an old set of speakers I have. The speakers are crap JBL floor standers with a 10", 4" and 1" tweet.

The case is pretty small and the volume is way too small for the drivers, but this is not about high-fidelity sound.

I think i will use the stock crossover that come in the speakers, but i need a small battery powered amp. the speaker can take 100w and arent very efficient. i would like to have 25-50w @ 8ohm. i have looked at parts express and havent seen an amp that fits this description. I would be willing to build one from a kit, but was hoping to buy one assembled.

I am just going to put a power switch, volume control and a 3.5mm input on the top of the case.


Here is my inspiration:
http://theboomcase.wordpress.com/gallery/

i doubt these sound very good, but they sure do look cool!

Thanks for the help!

 

[SavidSelim]

http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-300&source=googleps

this looks like a great amp for the boombox. anybody have experience with this type of amp?

 

[annunaki]

That amplifier will require a 14VDC constant power supply. They sell the power supply separately at PE.

I am not aware of a battery powered amplifier but I am sure one exists. You will want to go with a lower power solution here to avoid draining your battery too quickly.

The other issue you will have here is that the efficiency your speaker has now is also much in fact due to it's enclosure. A driver works with the enclosure to generate sound. Putting the driver into a very small enclosure that it is not well suited to will result in decreased efficiency.

This is an interesting idea but will require some thorough planning to execute it well.

 

[lsiberian]

The 2 channel sure amp is very solid. Diyaudio has threads on the amp with help from the manufacturer.

 

[j_garcia]

PE has the t-amps on sale this month. They don't have a lot of power, but they can be battery powered last time I checked.

 

[SavidSelim]

Thanks for the replies! I will look into those t amps. A friend of mine builds batteries and will be taking on the task of building me a battery pack and charger. I am hoping to add an ac adapter port on the case as well for recharging.. This will be MONO, so i could use a very simple amp.

I am building the speakers config tonight after work. Ill post some pics of how it looks when i am finished.

 

[SavidSelim]

would this be a good amp choice?
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-385

its only 15wpc. Could i bridge the hot speaker connection on both channels to make this mono?

I am in touch with somebody who can hopefully get my battery situation under control.

Here are the speakers i am taking apart:
http://manuals.harman.com/JBL/HOM/Technical Sheet/TLX181 ts.pdf

The crossovers on this are nowhere near what they should be for this size cabinet, but like i said.... this is not for sound quality! just for fun!

they are 90db, so maybe they will be loud enough with a small amount of power.

any suggestions? am i moving in the right direction?

thanks!!

eye candy:

 

[j_garcia]

The one you listed isn't battery capable AFAIK. This is the one I was referring to:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-380

 

[gregz]

Interesting project ya got there. Definitely a fan of a single subwoofer with enough air volume behind it rather than cramming two without enough space. I would spend some time looking at power supplies, and make sure you choose one that has the right parameters no matter if it claims to be good with batteries or not:

Input:

Obviously, you know you need a power supply that takes DC unless you're willing to expand your project to some circuit design. With a battery pack, reaching 12VDC is not difficult.​

Efficiency:

For battery operation, you certainly want to stick to a switching power supply for efficiency, usually called class D or H, all of which have efficiencies in the 80-90% range. The catch is that max efficiency is at a specific power output. Switchers also usually require a minimum output power to run, so you want to match the max output power of your amp to the levels you plan to play.​

Dropout Voltage:

Here's the spec that should show if a power supply is truly battery compatible or not. Unlike car applications, battery voltages drop as you use them between charges. You want a power supply that will keep working well below the rated input voltage.​

 

[gregz]

By the way, Annunaki's point is a good one on efficiency. Not only is the 90dB based on a larger enclosure with a passive radiator, but it could very well be achieved mostly through the tweeter and mid. The woofer itself could have an efficiency much lower.

If I were to make a boombox, I would base the entire design around a speaker, and I would start with a speaker that was as efficient as possible - definitely higher than 90dB.

I might even consider a car audio coax speaker for a simple, extremely efficient design.

 

[SavidSelim]

Can I not connect a 12vdc battery to a device that takes 12vdc as long as I am close in amperage? I am looking to get a battery made for me with a charger. I am not experienced in building electronics but my battery guy seemed to think it could work. I want an amp that will allow me to have an external power switch volume knob and 3.5mm input. I guess I could take that amp apart??

There is something I don't understand....

 

[SavidSelim]

alright, so the speakers arent optimal. i am going to test this with my 100w receiver today. you think i am going to have to hit this thing with lots of power?

i have the box semi assembled. the holes are cut, and i put some left over peal n seal in the case. i will need some more and some foam as well. i am getting hardware today as well.

i am assuming this little amp will not power this thing to any decent volume level.
http://www.parts-express.com/pe/show...number=300-385

my case is pretty small, with the woofer in place i do not have much clearance on the back. so size matters.

i can always pick up a bigger suitcase from a thrift store. they are everywhere.

i am pretty set on making something like this work.

gregz: thanks for the input on power supplies! i need to research this further. i might start with a plug-in version only. maybe with a car adapter or something. i am not experienced with batteries or building electronics.

 

[gregz]

Well? Did you hook it up to your receiver yet? How did it sound?

I'm still digging the whole look of this suitcase boombox. What a creative, wild and whacky idea! Aside from power and efficiency, the next difficulty - I mean challenge - will be the fact that even a hardside suitcase will flex in and back out if that sub starts to pull with any force.

Although most people making speaker boxes out of 3/4" wood panels go to great pains to add bracing to prevent even a millimeter of flex, this isn't the end of the world. There was a period of time in the 90's when many top automobile instal shops were experimenting with a partially flexible wall in the subwoofer enslosure that allowed a smaller box to be used for the same alignment. Your suitcase could be spot on, or way off, but there's always a chance it will work well with no internal bracing.

B.T.W., your latest amplifier link was a dead-end.