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Old 11th July 2012, 05:03 PM   #1
matros is offline matros  Denmark
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Location: Lyngby, Denmark
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Lightbulb [SOLVED] Small Festival Stereo, need help wth battery life and construction

Hey Guys
As many others I am very new to this diy stuff, but I am looking for some help in regards of the construction.

First off the parts I am thinking of using (if you have any inqueries about these let me know asap as I need to order very soon.)

Drivers: Monacor SP-60/8*
Tweeters: Monacor MPT-001
Amplifier: Indeed Class T Amp TA2020 Mini Amplifier 20WX2 Tripath
Battery: 12V 12Ah SLA (Not this exactly, but similar, dont remember the brand)

*I am unsure weather I should get 4ohms or 8ohms.

For the box itself I found some plywood around 1,2cm thick, lots of layers and with some brown coating - it feel very solid

So the plan is to build is kinda like the famous Boominator with 2 drivers and 2 tweeters on each side.
From a calculator online I read that the internal volume for the speaker should be 5,55L. But to this I have a question: Should the space be twice that size with two speakers? Or can I just mount them magnet to magnet and keep the same size?

I am making the depth according to the Tweeters as they are a little deeper than the drivers. Should I put something between the driver magnets?

Also. With this setup, how long do you reckon battery life would be?

I am studying to become an electronics engineer, but have never worked with sound and all that, so when you calculate stuff, please elaborate so I know how to do it for future projects if you dont mind :P

Last edited by matros; 15th July 2012 at 07:34 PM. Reason: Gotten all my questions answered elsewhere.
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Old 12th July 2012, 09:08 AM   #2
matros is offline matros  Denmark
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This is the datasheet for the batteries I have access to, do I read it right when it says:
20 hour rate (0,6 A - 10,5V) 12 Ah

Does that mean that discharging it with 0,6A for 20Hrs it will reach 10,5V ?
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Old 15th July 2012, 07:24 PM   #3
dangus is offline dangus  Canada
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Join Date: May 2004
Location: Vancouver Island
The capacity and discharge rate sounds right. But you should avoid discharging the battery that far. Consider building in a cheap eBay digital panel voltmeter so you can check the voltage from time to time (use a momentary contact switch so the voltmeter isn't an unnecessary drain). Battery life will depend on how loud you play it. Even at close to clipping, the average consumption should only be a couple of watts, so it might last an entire long weekend.

With two speakers, box volume should be doubled.

4 ohms (or two 8 ohm speakers in parallel) will allow you to get the most power from the amp. If you're putting two speakers on each side (for a total of four, ignoring the tweeters), then use 8 ohm speakers.

Larger speakers with lower power handling might get louder. Like secondhand car speakers, or factory car speakers that were discarded to install an aftermarket system. They'll be 4 ohms, though, so you could only run one per channel. You might get some for very cheap by asking at car stereo stores that do installations.
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Old 15th July 2012, 07:33 PM   #4
matros is offline matros  Denmark
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Hi Dangus, thanks for you input, I already have a voltmeter mounted, and with a switch so it isnt running constantly.

I am considering buys two 7,5V 5,4W solar panels, and connecting them in series to keep the charge on the battery. I got the battery from my work, and I know very well what happens when the voltage dips too low on those batteries, on that front they are kinda sensitive

I have already ordered the 8ohm SP-60, and gotten told to double the volume, so I am just waiting on the parts to arrive so I can get going

I am gonna mark this as solved, but if someone has questions, feel free to ask them at any time in this thread
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