Help building speakers

[guerilla_logic]

Hey guys i'm looking to build my first set of home made speakers. I have a 50 cal ammo box that i would like to put either 2 3.5 or 4 inch speakers in. I want to power it by outlet, and i would like it to be able to take input from either an MP3 player or laptop via 3.5 mm jack. My question is do I need an amp how to wire ect, I will be able to do all the box cutting without an issue I just need help on wiring and parts.

 

[Guest]

If you are looking to build a computer or MP3 speaker, these are normally powered (ie have a built-in amplifier). Hifi speakers generally don't -- ie you use them with a separate hifi amplifier or receiver.

How suitable are ammo boxes for the purpose -- can they be airtight sealed ? If made of steel can they be damped aso as not to rattle at certain amplitudes/frequencies.

My guess is, if you are going for the military look, best to buy some existing speakers already in boxes which will fit the new outers without much modification.

 

[anwaypasible]

if you want to use that box.. you need to find some speakers that will work best in that size of a box.
you can measure the box and find the cubic feet.. but it is best to compensate for the amplifier and the back of the speakers (unless you reverse them).
the way i was taught, first of all, you can sometimes get the volume of the speaker in the specifications.
otherwise you put the speakers in a bag so they are water tight and then dip them into a bucket of water filled to the rim.
you place the back of the speaker into the water like as if you were mounting it to the water with the rim of the speaker barely touching the water (or a few millimeters above the water is okay).
you let the extra water spill out.. then pour the rest of the water into a measuring cup to measure the amount.
you can translate the amount of water into air volume/cubic space.

you also want to do this with the amplifier.

anways.. you could try one of those amplifier kits on ebay for less than $20
you have to provide them with enough power.
and usually they require a weird amount of voltage.. 20v - 30v
this means you cant really connect it to an old computer power supply.
and the best option would be to purchase a toroidal coil that accepts 120v in and puts out 30v
but if you use a toroidal coil, i would suggest purchasing the seperate 'power bank' which is a bunch of capacitors to filter any jitter in the voltage input.
you could probably screw the transistor chips directly to the metal box for a heatsink.
and if you want added protection.. you could probably purchase a heatsink and screw it outside of the box directly where the transistors are.
a heatsink with double sided tape might work.. but it might get the glue hot and fall off.

its best to make the box air tight unless you tune the box for a specific frequency.
there are box and port calculators on the internet to help you decide.
but even with a port.. you dont want any air leaks because the holes will make noise and affect the air suspension of the box.
you probably dont want to glue it.. so use some kind of weather stripping to seal the lid shut.

you can purchase a headphone input jack from any electronics store like radio shack .. or purchase one online.
you want one that will screw into its hole with a lock nut.
that will give you an input jack that goes onto the amplifier.

the amplifier goes together like legos and is pretty easy with a soldering iron.
the circuit board tells you what goes where.
but if you want the amp to come prebuilt.. pay the small extra fee to have it done for you.
the power inputs and speaker inputs/outputs are marked.
all you have to do is put the wire into a screw clamp and tighten it with a screwdriver.

i would send you to parts express in search of some speakers.
but no speaker box is complete without having a crossover and tweeter.
you cant expect a single speaker to play the midrange and the treble unless you pay more for a 'full-range' or 'extended range' speaker.
parts express does have those speakers available.

i have had good luck with cerwin vega crossovers on ebay.. they are half the price of crossovers on parts express.

but the first thing you need to do is measure the box and determine the internal volume so you can get some speakers that will thrive in the box size.
the wrong box size can utterly ruin the output of the speaker ... a clear mismatch isnt always easy to do, so you might not know what you are missing.

this is probably the cheapest option with the highest results unless you purchase a prebuilt speaker system and try to glue the pre-made boxes in alignment with a cutout hole for the speaker.
i wouldnt advise it because there is more internal volume to use.. and that increases your potential of a full sound.
putting pre made speaker boxes inside the box will probably sound dull and lifeless (at least in the bass range).

maybe it would be best if you pick a sealed back midrange and choose the other speaker to be a woofer.. then get a crossover and tweeter to have yourself a three way system.
three way systems have a much broader frequency range.
and by choosing a sealed back midrange.. the woofer wont push on the other speaker because of the bass.

you can have something that sounds like a sony boombox from the early 1990's .. or you can have something that rivals an expensive bose speaker system.
it all depends on what speakers you choose (and amplifier) .. and then how much research you do selecting the right ones.
reviews dont always work because many people will praise a product simply because it isnt broken.
you need to rely on a brand name.
peerless has been used in quite a few hi-fi sound systems under a different brand name.
so has scan speak.

peerless india is not the speaker you want.. they are made in a different factory and have less quality.

 

[MEgamer]

id go for dipole design, and find the biggest driver that can fit in that 'box'.

 

[guerilla_logic]

Best answer selected by guerilla_logic.