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Old 30th June 2005, 06:31 PM   #1
jeebus is offline jeebus  United States
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Default portable backpack sound system

I'm planning to build a portable sound system small enough to
strap on as a backpack and walk around with it. I've seen
such a setup that wasn't too bad using just one 6x9. But I
was wondering what reasonably portable options would produce
the most sound.

Sound quality needs to be listenable, but doesn't need to
win any awards.

I was thinking two 6.5 inch speakers, but other people
seem to think one 8 inch with two tweeters would be better.
Or one 6x9 with two tweeters could be slightly more portable.
but I'm not sure how that compares to an 8" for bass.

Any opinions here for what would produce the best combination
of loudness and portability?
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Old 30th June 2005, 06:45 PM   #2
cratz2 is offline cratz2  United States
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Hrmm... you mention car audio speakers... I don't know if they would be the best option. Are you wanting adequate bass or would you rather have a bit less bass but with better sound quality from 100 Hz up? I can't envision what size you are wanting the entire thing to be, but I'd be tempted to try two Tang Band drivers and a single 'sub' about 5.25". Or I might even look into a 4" sub model though I've not done any research into them at all.
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Old 30th June 2005, 06:54 PM   #3
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When making a portable sound system you must ask yourself a few questions.

What is your powersource (batterys but what kind)?

What is your audio source?(cd player, mp3player, radio, etc)

What will you use for amplification(they sell wireless speakers that run off of batterys I've seen their amps used before and I think a car audio amp is a possible option also)?

How much weight can you hande?

How much do you want to spend?


Speakers should be a no brainer if sound quality isn't of utmost importantce. You want something with HIGH efficiency plain and simple. Not only will high efficency speakers increase your maximum output, but if you dont have to turn your amp all the way up for a reasonable level then you're using less battery power and you can play for longer.

if you want decent bass you're probably going to need an enclosure of some sort for the woofers. Since it's going to be on a backpack lightweight is a priority I'm sure and you cant just build a box out of some MDF. The easiest thing to do would probably find a plastic container(such as a trashcan planting pot etc...) and then fit your woofer into that. You might need to put some internal bracing in it, but if you're lucky you should be fine without it....
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Old 1st July 2005, 11:41 PM   #4
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Hmm.

Great idea by the way

There are probably 3 main ways of going about this:

1. is to go out and buy a pair of 3-way 6x9's from some auto shop and build them into a basic tuned box, stuff a sealed lead-acid battery in it (try looting around at dumps in the battery banks for old fire alarm batteries - they're often chucked out without being tested because they can't take risks... or just buy some ) and an amplifier, and you're good to go.

2. involves doing some research into drivers and cabinet arrangements, and coming up with something to suit the application. See my application ideas below :P - this takes time, but can be oh so rewarding.

3. is to suck it and see... buy some cheap buyout drivers (the 49c tweeters from Parts Express and 99c NSB's are good for the higher end, then if you get some 5" drivers etc from PE as well for like $8, you're good to go) and design cabinets for each one. Make it so the subwoofer part is downward-firing or something, with the tweeters and NSB's pointing out at angles for maximum spread, and experiment, rather than fiddle about at the design stage for weeks on end.

You're basically building what the oldies on here would call a boombox... back when you couldn't pick one of these up, people were building them themselves, on the cheap as well)

What I'd do is go for cheapo end-of-line 'buyout' drivers and have a damn good play around with them design-wise. A pair of 4 to 5 inch drivers in a nice sealed cabinet would work nicely for the all-important low end, and some NSB's with tweeters would serve the mid and highs well.

I actually built one of these before, the only difference being it was a cheap set of 8" drivers with piezo horns in a box that I bought for like 20, and put a car radio reciever and a pair of UPS batteries in. Worked damn fine with a radio transmitter (it was legal.... honest )

See, you can do it cheap, and you can do it cheaper. the only variable is time!

Hope this helps

Karanael
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Old 1st July 2005, 11:48 PM   #5
dnsey is offline dnsey  United Kingdom
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As far as the amp's concerned, class T must be the way to go.
Efficient, light, cheap and remarkably good sound into the bargain!
Suitably enclosed Jordans might make interesting speakers...
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Old 2nd July 2005, 02:48 AM   #6
AJinFLA is offline AJinFLA  United States
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I seen this question before and it looks like I'm going to have to build one for the heck of it just to show what I mean. For SQ in a very small package, I would go with a 5-7" coaxial car speaker mounted on a OB with folding wings (ie. the "sides" of the u-shape). You sacrifice bass, but end up with compact package and OB clarity. Depending on the amp used - here is an example of reasonably HE, but @ 2ohms!
http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW
There are many others for less $ of course. Smaller drivers also.
Here are my computer speakers, wings fixed. Sound great.
Could be made much smaller for portability.
Click the image to open in full size.

Cheers,

AJ
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Old 2nd July 2005, 08:16 AM   #7
jeebus is offline jeebus  United States
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Sorry for not getting back very quickly to answer everybody's followup questions. Been busy with the 4th of july weekend coming up and all.

Thanks for all the input. I'll try answering all the questions I can:

Total size: I haven't decided either, but around 10 pounds ought to be fine.

Bass vs overall quality: my guess is bass makes for more of a party atmosphere which is what I'm going for, but I'm happy to change my plans if I'm wrong about that.

Power source: I was assuming I'd go with a motorcycle battery (which I already have, although mine isn't gel). And I was going to use that to run a car amp, which I don't yet have.

Audio source: mp3 player.

Money: I could spend some money on it, but don't really want to dive straight into the deep end. If I later find that carrying this thing around isn't as much fun as it sounds, then I don't want to be out a huge sum.

I like the two 6x9 idea, except I'm afraid that might be too bulky and heavy.

I also like the idea of just experimenting with low end components and see how it goes. I'm afraid my cabinet building skills are very weak, especially when it comes to making something that's supposed to be comfortable to wear. But what do those acronyms stand for? (49c tweeters and 99c NSB's) Did I mention I'm new at this .

And of course I like those infinity kappa's. If I'm understanding efficiency ratings and such, 2 ohm and 94dB sensitivity is fantastic. Is there a down side? They're not cheap, but not ridiculously expensive either.

Why OB? (stands for open box I assume?)
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Old 3rd August 2005, 06:54 AM   #8
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hey mabye you could get an old boombox and switch it for 2 6.5coaxals and a couple of tweetwers
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Old 3rd August 2005, 06:58 AM   #9
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well i would get a backpack with 2 nice large pockets and padd the h*** out of the one nearer to you and mabye put your cheep car amp in it and then just make the small speaker boxes that would fit the other pocket
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