Foam, Cardboard Horn? autosub? Ultra-efficient battery powered PA system required! - diyAudio
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Old 14th January 2007, 11:54 AM   #1
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Default Foam, Cardboard Horn? autosub? Ultra-efficient battery powered PA system required!

Hi,

This relates to a previous Class-D amp post with some back-ground : Portable PA requirement - need input please.


Bascially, I'm trying to figure out the best design for an ultra-efficient, portable (towed by a bike while playing), and battery powered PA system. It doesn't need to be Hi-Fi by any standards but half-decent and importantly LOUD.

Originally I was looking at a dual bandpass box as they are loud, even though every one I've heard sounds pretty awful. More recently it's been suggested to try a Bass Horn, possibly made from lightweight Foam-Core or 'Foam board'. I've obtained the plans for the 'Autotuba' but recently found that the response chart I was looking at was compensated with the enclosed cabin gain of a car.

Bearing in mind my aim is to to get a lighweight, efficient thumper, has anyone got any options on using an autosub design in an outdoor environment. Or point me in another direction?
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Old 14th January 2007, 08:09 PM   #2
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Location: Rotterdam, NL
Quote:
Someone mention to me once that a bandpass box can be more efficeint even than a horn design, does anyone know if thats true for the same box volume ?
There is a relation between box-size, low end extension and efficiency.

Bassically you can have a small and loud box but trade-off will be the low end extension.
For a given box volume a bandpass build for efficiency could easily out run a horn which is build for low end extension and vice versa.
However horns are generally build with the eye on efficiency rather than extension.
The low end extension is reached for by stacking multiple bass horns together, as a solid 30 Hz from a horn with maximum efficiency in mind, would require a small bike-truck to tow.

A relative small or band pass horn aimed at 55-65 Hz and up depending on desired music style. Actively crossed at 120 - 180 Hz to an top that is designed for 120 -180 Hz and up. That top could either be hornloaded or use a 12 or 15" with an efficiency like 3-5 %, combined with a 1" or similair sized compression driver. All neodymium of course.

That neodymium will go for the sub as well. Reflex loaded I wouldn't mind using anything smaller than a 15" or 18", as a bigger Sd is the way to go loud with little power. Personally I wouldn´t use reflex at all unless I had the power (which you don´t).
For hornloaded 12" could do aswell but a 15" or 18" wouldn't be a bad thing anyway.

Some capable bass cabinets I would take a closer look at would include, the HD15 (speakerplans), Tuba 24 (Bill), Punisher (only in combination with foamcore) and some 15 or 18 inch BPH´s floating on the web. http://www.speakerstore.nl/index.php?l=nl&pg=5

I don't know the quality of the foamcore. Yet I do know that certain types of foam or honeycomb (thickness 1/2" and up) with on both sides 3 mm quality ply can be more than adequate for your goal.

As for the bike car itself, use the smoothest sliding wheels you can find and make sure the coupling to the bike is really good, if not it can swallow loads of energy, making just 90 pounds a real drag.

Wkr Johan
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Old 15th January 2007, 09:07 AM   #3
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A base structure of foam then sprayed with truckbed liner or another such strong material (fiberglass would be more expensive probably..) might allow you to make the horn.
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