And we're back...
Here's a little back story on this cab and the thought process. About 6 months to a year after completing and testing the Othorn's I started thinking about something that would go "further" and hopefully improve upon Othorn. I have been really happy with the Othorn both from a perspective of the measured results and the subjective results. It's one of my favorite subwoofers for pure music listening at stupid levels. It just does something right. A lot of others tend to agree. I don't know how many people have built them but it's far more than I ever expected. There's a guy with 16 in his inventory from what I hear. That said there are a few things I felt could be improved on.
#1 Cut down on cabinet and panel vibration near the driver.
I have found that one of the main weaknesses in tapped horns is the area under the driver near the mouth. This is often a single sheet of material with a large area which can only modestly be braced, if it is even braced at all. It makes the build easier and makes sense as far as folding most times, but it is subjected to a lot of force. In the Othorn this area is braced fairly well compared to many TH's, but the hatch will flex and vibrate quite a bit once it really gets pushed. Placing the hatch area down takes care of most of this, but sometimes cabs need to be placed horizontally. With a 450g moving mass and a lot of pressure in the Othorn cab it will also tend to "hop" when pushed hard.
#2 Improve the fold or reduce build complexity.
The Othorn horn fold I've always felt was quite ugly with 3 90deg folds. There are some odd angles and tricky pieces to fabricate in there as well. It's a product of cramming a huge driver and enough path length for extension down to 25-30Hz into such a compact package. It is not elegant by any means and I've never been that happy with it.
#3 Higher performance.
Of course I always want to get just a bit more out of the same amount of space so improvements in overall efficiency, voltage sensitivity, excursion limited headroom, power handling and output compression are always a priority.
#4 Driver options.
Most people that build the Othorn's do seem to use the recommended 21 or 18" drivers but there have been a few who have used much more affordable / weaker drivers that simply do not perform right in that cab and won't allow it to perform like it should. Usually if someone isn't happy with the Othorn it is because they skimped on the cabinet build quality or used a driver that isn't compatible. With that said it would be nice if a newer design was more tolerant of other drivers.
I originally went with a refolded tapped horn the Palehorn in the same cabinet form of 24x36x36. The fold was much better and did address the weak areas under the driver hatch so that the amount of panel vibration should be much less. The overall cabinet should be much sturdier. The path length ended up just a bit longer though and the Othorn was already using one of the highest output pro drivers available so it probably wouldn't have gained much in the overall performance department. Being a TH it was still very driver dependent and only the same few very expensive drivers that would work right in the Othorn would work in the new cab. At the end of the day the PH would've somewhat addressed item #1 and #2 to some extent but did not address #3 or #4 on the above list. Overall I'd call it an improvement but not as big of one as I'd like. I also worked on the Gjallarhorn design for exactly the same reasons at the same time and I did release that design update as GH v2 with the improved cabinet design. I probably will release the PH cab design as a final update to the Othorn as a sort of v3 whenever I get around to finishing the print.
What I really wanted were new cabs that would outperform the GH and Othorn so I kept trying things until I found some simulations I liked with the quasi 6th order BP horn that resulted in the M.A.U.L. and this new Skhorn cab. The M.A.U.L. got completely out of hand since it would be a one off personal project that no one else would be building. However since it matched the simulations quite well and in most cases it has the potential to outperform a pair of GH's from only 36% more space I'm quite happy with it. The M.A.U.L. is what convinced me to go ahead with this type of design and tweak and finish off the Skhorn design.
I am happy with the bandwidth covered by the Othorn for loud music or reinforcement applications (25-100Hz). One way to easily make a sub seem more powerful is to sacrifice extension. It'd be easy to make a 40Hz extension sub that is loud as hell but those types of cabs have been around for decades. Personally I just find "subs" that really only extend to 40-50Hz or higher just miss too much of the bottom end of modern music. Notes come up M.I.A.. In my opinion a real "sub" needs to be able to produce a legit powerful 30Hz at minimum or it's just a bass bin. That means I wanted similar extension as the Othorn for the new design. That being the case, since I want the new design to be able to outperform the Othorn and it is already using one of the most powerful drivers available, there's really only 2 ways to make that happen. Make the cabinet larger due to H.I.L. or use more power and have higher displacement and multiple drivers. If you want significantly higher headroom you do both. To that end I decided I'd go with a slightly larger cab with a form factor and size similar to the large dual 18" vented pro cabs on the market. I tried my ass off to miniaturize down an 18 or 21" tapped horn even smaller than the Othorn, so I could join them in a dual cab while maintaining that type of extension and logistically it is just a nightmare. I just couldn't get it to work without severe compromises. Now if you drop to 12 or 15" drivers it can be done but I'm not about that life. The BP6 horn deal does quite well in sizes even smaller than practical TH's with a deep tuning so I was able to compact it just enough to make that happen. The overall design is a bit simpler than folding up a TH as well. With dual drivers it seems to be able to offer some performance advantages from a cab only marginally larger.