Do you remember that huge design I was planning? the like 300 cubic foot bass horn, 40 Hz flare in half space, 4,500 sq inches of mouth and around 12 feet of horn length?

I've been contemplating for a very long time about how to build this thing and still keep it mobile. My first idea was to just build it all out of plywood, which I can do, but the weight woudl be huge. I am guesstimating about 700 pounds of plywood per horn.

My second design was to use a sandwich of 1/2" plywood and expanding foam. The idea is to use a 1/2" inner horn wall, use perhaps 2x6's as "studs" every 16" (almost creating a wall like building a house) and then another 1/2" layer of plywood. After that, I could fill all the cavities with mass amounts of expanding foam.

My third idea was to pretty much engineer the whole thing out of solid styrofoam, maybe giving the actual horn walls a couple of layers of fibreglass. Only trouble is, that much fibreglass woudl be very expensive and I don't even know where to get styrofoam chunks that huge.

If you recall the design, it's rediculously huge. The mouth is slated to be 8 feet wide and 4 feet tall, with the largest unit being 4 feet deep as well, with a smaller bolt on section making up the rest. So pretty much, the longest length that needs to be braced is roughly eight feet. Also figuring I can only use cross bracing inside the horn mouth no more then every two feet.

Also, I'm wondering what happens when you load a single horn with multiple woofers. If I were to load this thing with four JBL 15's as opposed to my original single 15" plan, woudl I also have to make the mouth area and everything four times a large? Or can I just quadruple the rear and front compression chambers?

Thanks man... With some help, I'm hoping to get a revised design up soon.

Adam

Adam

That limits your choices, doesn't it? Of course, if you didn't need to be movable, you could make a structure from concrete - Something like an ampitheater. But if you must be movable, I have another good suggestion.

I would make two large panels, perhaps having wheels on the bottom. The two panels would make sides of the horn and the ground makes the bottom - Something like what I use the walls of a corner for in the cornerhorn. If you want a curved flare, then you can make protrusions that narrowed the area closest to the motor chamber, in order to constrain the throat.

Something like this:

For the panels, I would probably build a framed structure like the walls in your home, using sandwiched expansion foam surrounded by reasonably thick wood panels. For installation, bring the two panels together at their apex and have them firmly clamped together. They should be tied together along their length with braces put along the top and bottm, or perhaps with guy wires or rods holding them taut.

I'd avoid building an entire horn structure, because it will be hard to keep it from being "flimsy" at this scale. But the panels probably wouldn't be too hard to work with, and your motor chamber would simply sit in the corner. It can be a box that is shaped like monitor speakers having a diagonal face, and you can load several drivers in the motor chamber cabinet. Even MF/HF subsystems can be placed within the horn if it had a conical flare or a curved throat shape that wasn't constrained too much.

Like the design I am considering uses multiple sections that can be detached, moved seperately and bolted together. It woudl be a huge task to move them around, but that's life. I moved a 1,500 pound trebuchet that's 35 feet tall, four feet wide and sixteen feet long from my house to a grassy field with only a trailer, myself and my dad, I think this thing will be a synch in comparison. :)

So, what kind of increases will I see if I use multiple woofers? Will I see the usualy +6 db gain from doubling the number of subs?

If I use four subs in one horn, that is four times the cone area and four times the power input (just assume that second point for a second) so I should be getting +12 db max output over a single driver design, and +6db sensitivity over a single driver, right?

That woudl put the sensitivity of this bass horn at around 112 db/1w/1m... pretty sweet! :P

Also, is it possible for me to split the horn into two sections partially down the line? I know it's possibe actaully, I'm just not sure how to do it.

I mean like an "M" shape, with the center being the mouth, and then the horn splitting into two like a mcdonalds crest, and having two of the woofers at each end. Obviously each individual horn woudl still have to have the same area as the bigger single one, but when they combine, I'd have to immedietly cut it in half... I know that sounds really confusing, I'll draw a diagram if you don't really follow me.

Thanks for the help, Wayne.

Adam

Keep us posted on your progress!

I gotta see this thing when you're done!

I'm aiming for a fall construction date, I'm not sure when I'll get the woofers, though.

Trying to catch another tent sale. After seeing the prices of the tent sale, I simply refuse to pay the retail on the JBL 15's. I couldn't live with myself.

I'll keep updating.

Adam