How on earth do you expect to get 60 cubic feet of horn out of two sheets of plywood? My 32 cubic foot "DH horn" takes 3.25 (13 sheets builds 4 boxes). And very little scrap. There is more than one full sheet just for all the innards. It was designed specifically to fully utilize 4x8 sheets and pack into a horse trailer.
You can cut the outer 4x2x3 (24 cubic foot) FLH box out of two sheets, but I'll be surprised if you can get the innards out of that last half sheet, considering you want a 96 inch path. A well stocked scrap pile might help. The box would be big enough to get useful 40 hz out of, but would be more like 6dB down in singles. You might want two.
You can cut the outer 4x2x3 (24 cubic foot) FLH box out of two sheets, but I'll be surprised if you can get the innards out of that last half sheet, considering you want a 96 inch path. A well stocked scrap pile might help. The box would be big enough to get useful 40 hz out of, but would be more like 6dB down in singles. You might want two.
Steve,
Might as well edit "under 60 square feet external" to "under 60 cubic feet", and specify the SPL output you desire in half space while you are in the edit mood ;^).
60 cubic feet is 1680L. That's not a small box, and will likely need more than 3 sheets of wood.
Anyway, with a big front-loaded horn, you can do it. I used a decent RCF 12" driver in my sims since that's what I happened to have loaded in Hornresp.
This achieves 129dB from 43Hz upwards from a single 12" driver, in a box a smidge over 3000L net. With wood added for folding etc, it might end up 3500L.
Vrc: 56.16
Lrc: 41.50
Vtc: 1345.55
Atc: 530
S1: 132.5
S2: 38436.24
L12 (Hyp): 420.77
Good luck folding it.
IMO, the specs you're hoping to achieve are borderline ridiculous. For a 12" driver to do that SPL in a sealed box, it'd need a little more than 4" of one-way travel. A big horn gets you some leverage, but you're looking at 3 cubic metres of horn. By the time you've bought all that wood, you could've got a nice pair of 15" drivers, a few kilowatts of amplifier, and done the same thing in less than 200L.
Chris
Anyway, with a big front-loaded horn, you can do it. I used a decent RCF 12" driver in my sims since that's what I happened to have loaded in Hornresp.
This achieves 129dB from 43Hz upwards from a single 12" driver, in a box a smidge over 3000L net. With wood added for folding etc, it might end up 3500L.
Vrc: 56.16
Lrc: 41.50
Vtc: 1345.55
Atc: 530
S1: 132.5
S2: 38436.24
L12 (Hyp): 420.77
Good luck folding it.
IMO, the specs you're hoping to achieve are borderline ridiculous. For a 12" driver to do that SPL in a sealed box, it'd need a little more than 4" of one-way travel. A big horn gets you some leverage, but you're looking at 3 cubic metres of horn. By the time you've bought all that wood, you could've got a nice pair of 15" drivers, a few kilowatts of amplifier, and done the same thing in less than 200L.
Chris
No, more like that the person answering needs to think a bit before the answer. This is how it works in real conversation right? Instead of becoming dead silent after a question, the respondent indicates that the question is received but is not ready to answer. The Um is just the written variant. Not necessary but again, indicates that the answer took some time to identify. Rudeness usually comes out much more clear
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Steve,
With those parameters, your horn won't do what you want it to do.
You've simulated 135v RMS input, and you're allowing the unit to reach Xmech. It'll sound bad, but not for long - that's a lot of power input, and the driver will burn quickly if subject to those power levels for anything other than very brief periods.
I hit Xmech a couple of times on a nice 15" subwoofer driver, and the cone folded. This was under extreme testing conditions - a ported box driven a couple of octaves below tuning with high power sine waves.
I don't think anyone else here would ever design a cabinet that has to hit the driver's Xmech to live up to specs. Xmax or Xvar (for B&C drivers) is the one to use.
When it comes to folding difficult shapes, my recommendation would be to draw the expansion out on paper, and then cut out each section and re-arrange the sections until you've got something that works.
It was recommended that you keep the final expansion, but have it flat-packed or whatever so you can construct it and bolt it to the original horn. Leaving it out will lose you output and LF extension.
Chris
With those parameters, your horn won't do what you want it to do.
You've simulated 135v RMS input, and you're allowing the unit to reach Xmech. It'll sound bad, but not for long - that's a lot of power input, and the driver will burn quickly if subject to those power levels for anything other than very brief periods.
I hit Xmech a couple of times on a nice 15" subwoofer driver, and the cone folded. This was under extreme testing conditions - a ported box driven a couple of octaves below tuning with high power sine waves.
I don't think anyone else here would ever design a cabinet that has to hit the driver's Xmech to live up to specs. Xmax or Xvar (for B&C drivers) is the one to use.
When it comes to folding difficult shapes, my recommendation would be to draw the expansion out on paper, and then cut out each section and re-arrange the sections until you've got something that works.
It was recommended that you keep the final expansion, but have it flat-packed or whatever so you can construct it and bolt it to the original horn. Leaving it out will lose you output and LF extension.
Chris
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S4 is at the mouth, and S3 is at the back corner. L23 goes up the back, and L12 gets folded back over, possibly multiple times, until you reach S1. Where to include the bends (as part of which segment) depends on where they fall. It will take trial and error. You may or may not end up with an outer box that works well - and may or may not be efficient in terms of wood usage.
If you approach it from the angle of letting the break points between segments be flexible, you can force it into a given box (provided its big enough). Let S3 be at the back corner of a known dimension. Force both ends of the bend to fall directly on the curve of the ideal hyp/exp expansion, following the "advanced centerline". Do the same for S2 at the top rear. The lengths of these segments and thru the bends form L34 and L23. If you run out of space to fit L12 and the driver chambers you need a bigger box. If there is wasted space it can be shrunk. It will take several paper iterations to optimize.
For an offset driver, you have one extra segment to the back short (hyp/exp expansion starts at S2). Now you see why I prefer a 3 segment approximation. OD's are easier to build, but with S1 = 108 it may be a bit iffy with a box of these dimensions. Keeping the outer walls parallel all the way to S1 may or may not be possible. Part of L12 may have to expand in x and the other expand in Y. For a box width close to the driver diameter one direction usually works (say width=21 or 24 inch with an 18 inch driver). It would get awfully narrow with a 12.
If you really want to build this you will need to spend some time playing with it on paper and drawing it out on a 4x4 piece of cheap plywood. I keep a bunch of cheap 3/8 inch on hand just for laying out horns - and I keep the ones I end up using so I have a template to build more later.
If you approach it from the angle of letting the break points between segments be flexible, you can force it into a given box (provided its big enough). Let S3 be at the back corner of a known dimension. Force both ends of the bend to fall directly on the curve of the ideal hyp/exp expansion, following the "advanced centerline". Do the same for S2 at the top rear. The lengths of these segments and thru the bends form L34 and L23. If you run out of space to fit L12 and the driver chambers you need a bigger box. If there is wasted space it can be shrunk. It will take several paper iterations to optimize.
For an offset driver, you have one extra segment to the back short (hyp/exp expansion starts at S2). Now you see why I prefer a 3 segment approximation. OD's are easier to build, but with S1 = 108 it may be a bit iffy with a box of these dimensions. Keeping the outer walls parallel all the way to S1 may or may not be possible. Part of L12 may have to expand in x and the other expand in Y. For a box width close to the driver diameter one direction usually works (say width=21 or 24 inch with an 18 inch driver). It would get awfully narrow with a 12.
If you really want to build this you will need to spend some time playing with it on paper and drawing it out on a 4x4 piece of cheap plywood. I keep a bunch of cheap 3/8 inch on hand just for laying out horns - and I keep the ones I end up using so I have a template to build more later.
...or map it out in a spreadsheet and use Excel's Goal Seek routines to provide the optimum results
If you can provide a sketch of what you're talking about, I might be able to fit an Excel workbook to it, similar to what I've done for the other horn folds at The Subwoofer DIY Page - Horn Folding
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