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Old 9th June 2010, 03:57 PM   #1
Rallen is offline Rallen  Denmark
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Join Date: Jun 2010
Default Project: Building a portable outdoor-stereo

Hey there.

I'm about to start a project of building a portable stereo for outdoor use.

My ambition is to create a stereo which is able to play loud, with a decent sound as cheap as possible, and in a cabinet which is as small as possible.

The only thing I know so far is that it's going to be based on the AMP6-BASIC amplifier.

From here on, I need to find batteries, speakers and a solar panel.

Any recommandations on those things are highly welcome!

But first of all, I'm most interested in finding the speakers i should use. Which should I look for?
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Old 9th June 2010, 04:21 PM   #2
Hitec is offline Hitec  Finland
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Join Date: Jan 2010
Look for sensitive (~efficient) speakers. The amplifier should be efficient too (class D?). The battery should be light but high capacity.

I'm about to reveal my own project soon . It is based on an amplifier with an SMPS (12V -> +-30V, SG3525 controller) and TDA8920B as a class D amp cicuit. There are 2 8" elements and one piezo tweeter. The batteries are lead-acid units but for light weight one could search for li-ion batteries.

Oh and larger speakers are usually more efficient.
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Old 9th June 2010, 04:28 PM   #3
Rallen is offline Rallen  Denmark
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Join Date: Jun 2010
Thanks for your reply!

Do you happen to have a link for a suggested speaker?
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Old 9th June 2010, 04:50 PM   #4
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Join Date: Dec 2005
Location: Berlin
Hey, i was thinking about that myself!
My current system (non-diy) uses 2 Tripath 2024, 2 fullrange speakers and two woofers in a dipole configuration. It is powered by a lithium-ion battery which lasts for around 5 hours. Even though i like it very much, it is a bit weak for my taste, i would like to have it a bit more powerful...
Two things that are really important:
The speakers have to be seperate, the difference to have a nice wide stereo panorama is huge compared to a single unit.
Also the input sensitivity has to be quite high to get the full power with low-output mp3 players (most are).
A fun project, good luck with it!
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Old 10th June 2010, 05:05 AM   #5
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Join Date: May 2007
it's too bad that size is a concern. you can get "free dB" by doubling your speaker count. every time you double your speakers, you get 3dB more output or the equivalent of doubling your amp's power.

if they weren't so expensive, those little 2" tang band drivers could put out 94dB with just 8 per channel & take up very little space. it's really hard to get efficiency in a small package. those high efficiency 6 1/2" & 8" fostex full range drivers are crazy expensive too, and wouldn't last outdoors anyway as UV would destroy their foam surrounds. DON'T use foam surrounds on outdoor speakers. use rubber, cloth or accordion surrounds.

a ported design will give you maximum bass efficiency and you can also get some extra dB making a folded horn design. that could get quite heavy with wood, but you could make it work in fiberglass though.

if you're aiming for light weight & portability, li-po rechargables are your best bet followed by li-on batteries. if you're maxing your power, run time might be an issue.

if you want max SPL without spending a fortune, i'd say get a dual coil high efficiency 12" PA (eminence, B&C, selenium etc.) sub and either use passive piezos or design crossovers for horns sort of like a portable subwoofer with satellites. that's how you'd get maximum bass boom for your buck.

i tell you though, you can get pretty decent volume out of just a 10wpc amp pushing small 86dB efficient 5 1/4" 2 ways. i've seen a lady get up and dance to "play that funky music" by wild cherry at around 50 yards biking through a park with my ports plugged at that. if you went with 93dB+ 6 1/2" or 8" ported woofers with extra power too, you should get nice output unless you want to throw a giant party.

you could build 8" high efficiency 2 or 3 ways, but you won't get a lot of bass out of them, especially with the 95dB+ models. the higher the efficiency, the more bass rolloff you'll get.

if bass isn't your biggest concern, you can get jamo (JVC) 8" white paper cone "woofers" for just $7 each at parts express. i bought a few to tinker with and they're rated at 91dB. they're very light weight (under 2 pounds i estimate) and could give you 97dB if you used 4 per side, but they have absolutely nothing going on under 100Hz. i was disappointed as their specs claim 40Hz-2.7khz and wanted them as subs only, but they do play pretty loud from the midbass on up.

Last edited by budget minded; 10th June 2010 at 05:19 AM.
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Old 10th June 2010, 05:57 AM   #6
Hitec is offline Hitec  Finland
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Join Date: Jan 2010
MGR F-2008W is the speaker we have used. It is 8", 91dB sensitivity, 35-5000Hz freq. response, available in 4 or 8ohm versions (we have 4ohm) and ~20€ price . The sensitivity could be better, but as far as I remember, it was difficult to find speakers with good sensitivity and good frequency response (if you find better ones, tell me!). There is also one MGR piezo tweeter. The sound quality is "good enough" .

In the very first version we utilized some normal coaxial car speakers but they both blew up. They were meant to be used in free air while we mounted them in a closed box so maybe that was enough

Our first intention was to use li-ion batteries but since the lead-acid batteries were widely available and could be charged with normal car chargers, we picked 4 x 4.5Ah 12V batteries to the device. They give power for a long time (don't really know yet for how long but >5h is my guess). We tested the second version for 7h with almost full power and there still was energy left in the batteries. The second version had the same class-D amp but no SMPS which takes part of the power.

So pick efficient speakers, class D amp and li-ion batteries for light weight.

Forgot one thing: outdoors you maybe don't need the lowest frequencies in the sound so you could filter them out for example below 60Hz or so. This improves battery life too since great part of the music energy is concentrated on the low frequencies.

Last edited by Hitec; 10th June 2010 at 05:59 AM.
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Old 10th June 2010, 06:08 AM   #7
Hitec is offline Hitec  Finland
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Join Date: Jan 2010
Originally Posted by budget minded View Post
you can get "free dB" by doubling your speaker count. every time you double your speakers, you get 3dB more output or the equivalent of doubling your amp's power.
I don't understand this . Why does adding speakers affect the speaker efficiency? Or did you mean this (improving efficiency, not the power)?
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