Portable PA requirement - need input please.

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biggerbyfar

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#1
Hi,

I'm trying to spec a portable, battery powered PA system towed by a bicycle or possibly a tandem. It's meant for serious sound on the move, not just transportable. 😀

Obviously this needs to be LOUD and relatevely lightweight and efficient because this is a battery powered beast. Hi-Fi quality is not really relevant, so long as it can throw out some beats.

So far, it looks like a 12" or 15" Neodymium woofer in a ported box or maybe a bandpass box if it can be made to work without getting too big. Just looking for effiency here. The mids and tops will be all horns. All running off class-D amps.

The bit I really need help on is the battery configuration, power rails and getting something like 2-300 watts from D amp. From what I see, you normally need somewhere near +-40v to reach this output. How can I do with with batteries (safely!) Strapping 8 SLA's together in series sounds like trouble...? Is it possible to invert upward *really* effiently to get the required supply?

Any other comments or tips appreciated. Can anyone point to some low(ish) cost class-D amp modules for this?

TIA

Paul.
 
#2
Search around for a Blaupunkt PA2150
Discontinued, but a good car amp.
Car amps include a SMPS to raise the voltage to what they need. So for the street price of around $100 this is a good deal for a 400w class-d (class-t) amp.

Consider horn loaded designs for the low end - it will make a world of difference on volume. See: http://www.billfitzmaurice.com/index.html

Look into using composite, or foam core plywood for lighter speaker cabinets.

Batteries will be heavy unless you spend a fortune on LIon
 
#4
Nigel Goodwin said:
When you say 'serious sound' what are you trying to do, and how much power do you think you might need?.

Be careful if you consider car amps, most of them have highly imaginative ratings!.
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This isn't for personal entertainment, more of a rolling street party... How much power? Enough to push a 12" or 15" bass unit to its near-limit without too much stress. Mostly dance-orientated music.

Car amps - I know they're usually very optimistic, but I wanted to stay away from them as efficiency is not usually a great consideration for them, and for me it is. I'm making that assumption that even with a class-D car amp.

I was wondering what the 'normal' approach would be to getting +-40 volts from a 12v supply. Switching PSU?
 
#6
biggerbyfar said:
Hi,

I'm trying to spec a portable, battery powered PA system towed by a bicycle or possibly a tandem. It's meant for serious sound on the move, not just transportable. 😀
Click to expand...

If you aren't aiming for the ultimate in quality consider using a folded horn made of cardboard -- (here in the states we have a product called "foam-core" which is paper sandwiching polystyrene foam -- rigid enough for a horn) -- you will get a lot more bang for the buck (pound?) increasing the efficiency of you speakers.

I guess Bill Fitzmaurice has been kicked off the forum but he does have a website.
 
#9
biggerbyfar said:
Do you know of any projects that have used 'foam core' for this?

Is foam-core like this -

http://www.paperstone.co.uk/prod_14...ckness-5mm-Colour-White-Box-of-10-Sheets.aspx

I've refered to it as foam-board before, and only used it for mounting photos onto, but it is very light and relatively stiff.... Is is the same?
Click to expand...

looks like the same stuff. when my wife and i got our first apartment and had no money (and no kids either) i built a horn design out of cardboard and it sounded very nice indeed. the foamcore will be lightweight and is quite easy to work with -- i would suggest that you use cloth tape to join the edges.
 
#10
i built a horn design out of cardboard and it sounded very nice indeed. the foamcore will be lightweight and is quite easy to work with -- i would suggest that you use cloth tape to join the edges.
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Sounds like bliss (no wood-working required!).

Was your design similar to this one ?: http://www.billfitzmaurice.com/autotuba.html

More questions:

How do you create structural bonds between the panels, like between a bracing piece and a sidewall?

When you say cloth tape, you mean like 'Duck' tape?

Know where I can find a 4 ohm neodymium subwoofer between 8" and 12" ?


TIA
 
#11
biggerbyfar said:



This isn't for personal entertainment, more of a rolling street party... How much power? Enough to push a 12" or 15" bass unit to its near-limit without too much stress. Mostly dance-orientated music.

Car amps - I know they're usually very optimistic, but I wanted to stay away from them as efficiency is not usually a great consideration for them, and for me it is. I'm making that assumption that even with a class-D car amp.

I was wondering what the 'normal' approach would be to getting +-40 volts from a 12v supply. Switching PSU?
Click to expand...


The only way to get 40v from 12v is to run and inverter/smps which will rob you of some efficiency. Or stack batteries.

I wouldn't assume all car amps in class-d are less efficient that you could make one. Look at their specs. Good brands will list efficiency.

Pioneer calls their class-fd (full range class d) look into them, but their not cheap.

The horn loaded speaker is going to give more DB and make more of a difference than huge wattage difference. This is a good place to start. I don't know about foam without some kind of skin and reinforcement, especially for portable use. There's other forums for that.
 
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