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Speaker in a Tin

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Georgeous0154 View Drop Down
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    Posted: 10 September 2016 at 1:34pm
Hello all.

I recently found some of these tins kicking around my house and decided to take on a project converting them into portable speakers. Until now they have just been used to keep nuts and bolts in.



I'm considering a 12v system with a 4" Faital Pro 4FE32 in one end, I've had trouble finding anything that will beat this sound and price wise. This will (probably) be powered by a fairly decent LiFePO4 battery as I'm looking for a good playtime and have space to work with here. I know there's a basic equation for working out life based on the mAh somewhere. 

In terms of Amp I'm a little lost and was wondering if anybody had any suggestions for me. I know I'm in need of a class D with 8ohm impedance but I would also like to be able to daisy chain multiple when built. Also will a 30W amp be unnecessary for volume and drain the battery quicker, I'm thinking of a high and low gain similar to that of the minirig.

If anyone could point me in the right direction or have any bright ideas I would be very grateful. 


Edited by Georgeous0154 - 12 September 2016 at 10:42am
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Hemisphere View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 12 September 2016 at 10:45pm
The equation for working out battery life is approximately amphours x volts = Watt hours, so 1ah x 12.6v = 12.6 Watt hours, then knock off about 15% for amp inefficiencies so call it 10 Watt hours, but music program is approximately 1/7 of the maximum output, so if you have a 10 Watt peak amplifier a 1ah 12.6v battery will run it at full blast for approximately 7 hours.

In real world conditions most amps are probably more lossy than that and other factors come into play, but it's a good rule of thumb to start from.

Your amp doesn't need to be 8 ohm impedence unless you buy 8ohm drivers. All aps you can buy will be able to run 8 or 4 ohms. If you're only running one driver per cabinet, try and buy a 4ohm variant, if running two buy 8ohms and run 2 off each amp channel.


If you're planning to run a single driver in a single cabinet in mono, you should get a mono amp as stereo amps don't really like having just one channel plugged in (it can be a cause of component failure)

For a basic low budget project like this you'd probably be fine with any of the TA2020 or equivalent Class D amps available on eBay, some will come with an enclosure with volume/power switch/led etc built in, some just as a bare board. I quite like the ones which are bare boards but also have a volume pot built in which double functions as an on/off switch, that would probably be perfect for what you're trying to do and you can get them for less than £10, that will drive 2x Faital drivers at 20w each which is just about the right amount of power for them.

Lastly I think you're going to find the baby milk tins will be the weak link in the chain unless they're a whole lot sturdier than they look, or unless you take significant steps to reinforce them from the inside.  You may end up spending £60-70 on the other components, but they won't sound much like a £70 investment if you mount them in a cardboard tube.

You could spend £10 on a metre of chopped strand mat fibreglass and a pot of resin and hardener and line the inside and perhaps the outside too with a few windings of that before painting, that could make all the difference, and maybe even something to brace it too. You shouldn't need to compromise on weight and cost much to add quite a lot of stiffness. Something will be a lot better than nothing.










Edited by Hemisphere - 12 September 2016 at 10:47pm
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Georgeous0154 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Georgeous0154 Quote  Post ReplyReply Direct Link To This Post Posted: 13 September 2016 at 12:29pm
Thanks for the reply Hemisphere. 

The tins are actually steel and would be reinforced inside and a wood effect plastic covering applied to the outside. I do like the fiberglass approach though, hadn't thought of that and have plenty kicking around. 

As for the amps I'm struggling to find any 20w mono amps on ebay. I would be running just the single driver, would it be possible to bridge a stereo amp or has this been known to cause problems? The best I have found so far is http://www.magenta2000.co.uk/acatalog/20W_low_distortion_mono__stereo_amplifier_module.html would this be suitable?

As for a battery something like this would run around the 7 hour mark judging by your equation http://www.alibaba.com/product-detail/2012-newest-Lifepo4-26650-12V-2Ah_211783371.html?spm=a2700.7724857.0.0.ycT73h

(Apologies, I'm not sure how the hyperlinking works on this forum)


Edited by Georgeous0154 - 13 September 2016 at 12:32pm
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Hemisphere View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 13 September 2016 at 4:35pm
Have you considered putting one driver in each end of the tin for a 360 degree sound? It looks like they have enough internal volume to accommodate two and there are several advantages (efficiency/bass extension) to doing this.

It's not that stereo amps can't be used to drive a single speaker by the way, I'd just heard it wasn't advisable. 

That kind of battery pack seems like it could work but really you're going to want one with everything included, BMS, charger/adaptor, that might not have either of those things and anyway that's a wholesale vendor.

Many people have had a surprising amount of luck with the cheapo battery packs being sold on eBay, like this one: http://www.ebay.co.uk/itm/DC-12V-3000mAh-Lithium-ion-Super-Rechargeable-Battery-Pack-AC-Charger-2368-EU-/291274043805?hash=item43d149319d:g:rLkAAOSw8cNUR4Eh


These are the sort of amp boards I was thinking of. If you buy a separate knob-cap to go with it, you could mount it inside the cylinder and have the potentiometer stick out the side as an on/off switch and volume control. 2x15 Watt so if you used two drivers one on each channel you've got 30w of amp power, plus a big boost in efficiency from using two drivers in a back-to-back arrangement you would get a very respectable level of output from this, and the efficiency is very high so even a small battery pack will last ages.

I've picked out some of the cheapest options available. The battery pack will only have about 500 full charge cycles but that's actually many years of constant use. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Georgeous0154 Quote  Post ReplyReply Direct Link To This Post Posted: 19 September 2016 at 11:38am
The idea of having a driver in both ends does seem to pretty beneficial, not to mention there are many more options when it comes to amps. 

As for the battery it was just to get an idea, it is possible to buy single units from alibaba so long as you don't mind a long wait for postage. There are some similar to the one you posted with a 2000 life cycle. Considering its a homemade project though parts can always interchanged so this isn't too much of a concern. 

Thanks for the head start Hemisphere!
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