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Old 13th July 2011, 07:24 PM   #1
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Default New and improved version of my Backpack-Boombox

Hello everyone

A few month ago I started building a simple backpack-boombox for use at the Friday Night Skate event in Copenhagen. It was a huge succes to say the least. Unfortunately it was put together rather quickly and build using cheap MDF plate, so it is only a matter of time before it will see rain and slowly disolve.
  • The boombox consist of the following components:
  • Amp6 Basis (Gain of 2.5, input capacitors will be changed to 0.22uF)
  • 2x Monacor DT-25n: neodymium tweeter.
  • 4x Monacor SP-60/8 connected in parallel to give 4Ohm input resistace.
  • A passive second order crossover filter which cuts at 2500Hz (let me know if you need details)
  • 7.2Ah SLA battery


The input is a line-out signal from iPad/iPhone/iPod.

The system is loud as hell and the sound quality when standing a few meters away is actually pretty good. The cabinet was build to fit into a old backpack but I think it ended up being around 15L, and is closed.

Before I start building the new version, using the same components, I want to be a bit more scientific about the box. So far I have calculated it in WinISD using 4 drivers, 16L, 65Hz tuning freq. and a vent diameter of 3.6cm and 1.8cm long. The box will be build using 9mm birch plywood, hence the 1.8cm vent

Here are a few screenshots of the simulation
http://dl.dropbox.com/u/2187315/boom1.png
http://dl.dropbox.com/u/2187315/boom2.png
http://dl.dropbox.com/u/2187315/boom3.png

The goal is the same as Saturnus' boominator. To have a peak around 120Hz and to ignore freq. below 100Hz as much as possible. Im completely new to WinISD so I would love to know if waht I have done so far makes sense.

This is what the old version looked like:

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/PalleRaa
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Old 13th July 2011, 09:10 PM   #2
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Interesting project. I'm interested in for slightly different aim.
How much does it weigh?
How do you manage to charge the battery?
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Old 14th July 2011, 07:24 AM   #3
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So far the top can be removed in order to pull out the battery and charge it. This will be change in the new version.

It weighs a lot. I think around 10-12 kg. The weight will be dropped a bit with the new design, but I doubt we will ever get it below 8kg.

The only thing holding me back is the question about the boxsize and tuning frequency. Is it correct to chose a tuning frequency equal to the Fs of the woofers?
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Old 14th July 2011, 07:45 AM   #4
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Quote:
Originally Posted by Palleraa View Post
The only thing holding me back is the question about the boxsize and tuning frequency. Is it correct to chose a tuning frequency equal to the Fs of the woofers?
That's fine.
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Old 14th July 2011, 08:51 AM   #5
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Ok, thanks. 16L it is then with a small'ish vent.

I wil update this thread as we go along. I hope this can serve as a nice smaller alternaive to the popular boominator.
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Old 14th July 2011, 09:05 AM   #6
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Quote:
Originally Posted by Palleraa View Post
Is it correct to chose a tuning frequency equal to the Fs of the woofers?
I'm not an expert...but perhaps I can help you a little...is it a bass reflex? If so you can tune it 2 or 3 Hz below Fs...it's all right even at Fs..
look at WinISD diagrams and you can't go wrong
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