UPDATE: This project ended up happening after all, just years later and with a 21DS115-8 instead of the original 21SW115-8. Marvelous results so far, feel free to check it out at:
B&C 21DS115 23hz 800L TH build
For posterity's sake, original thread is intact as follows:
Okay, I've got the Tapped Horn bug. I first became acquainted with the concept not long after I searched for information on a B&C 21SW115-8 I picked up fire-sale cheap ( $285 unused from a DJ going out of business in Utah), and ran across the Othorn. My driver doesn't model well in that enclosure and I'd trade some SPL for extension for HT ( my listening is about 50/50 music/HT). I am still on the early part of the learning curve and have a LOT to learn, but an evil idea is forming in my head.
After reading a bit on Little Mike's TH tutorial, I goofed around and found it was not hard to get a fairly nice looking curve on Hornresp, but the cabinet volumes were huge. Still, gaining a dozen decibels in the bottom octave over my current BR .... hmmmm.
My shop/furnace/laundry room is on the other side of the wall from my listening room in the basement, tons of room in there. Here's my line of thought:
I don't have a great many tools, or much experience woodworking, or money, or as much time as I'd like (who does? ). I would be willing to trade sophistication and complexity for size. So I'll want to keep the number of folds and joints as basic and few in number as possible.If it turns out to be 60 ft^3, so what. It's dead space I don't use anyway.
What if I built the body of the cabinet in the spare room, and opened into the corner of my listening room?
The preliminary models call for a pretty darn large mouth on the thing, if I'm understanding things correctly. What if I built the horn with the folds in the vertical plane instead of the horizontal, and brought it between the wall studs and flush with the room wall?
If I limited the horn mouth size to 3975 cm^2 (uh, yeah, kinda' big, I know....) it would come to something like a 45" X 13.25" opening through the wall.
It's a Man-Cave in a fairly crudely finished basement, and I'd have no compunctions about doing the modifications I've got in mind.
The output and response look pretty promising. I do NOT, however, understand enough about the other model outputs to be able to tell if it will be feasible.
My B&C is certainly not the driver of choice for a project like this, but it's the driver I have. It does have a few things going for it, namely it's rugged and well built, is made by a company that's going to be around for a while, and has a lot of Xmech -- 60mm --to work with. Josh Ricci was kind enough to reply to my inquiries as to what he'd regard as useable excursion, and he recommended up to 20mm, so I've modeled accordingly.
I'm still a bit confused as to how segment lengths and areas are figured: Is length measured by the shortest, or longest, sound path around a fold? Is the area measured perpendicular to the inside of the fold, or the outside? Rrrrr.....
But before I get ahead of myself, I would love some input as to whether my concept could work at all. What I hope for is a reasonable compromise that will get me through the next couple of years. I'd rather come up with something workable I can AND WILL build than something stellar I probably can't/won't.
Included are TS specs on the B&C 21SW115-8, Hornresp input parameters, and a rough not-to-scale sketch of what I have in mind.
A note on the sketch and Hornresp inputs. I'm trying to use inputs for L12 and L34 that can possibly match up onopposite sides of the baffle, since the mouth end of the horn will have to be at least a wall's width longer than the throat end ... lot of details to work out, but first things first.
Thanks ahead of time, I really want to make this work!!
21SW115-8.pdf 161k .pdf file TH concept.jpg 45k .jpg file TH Input parameters.jpg 103k .jpg file
TH 2.83v Response Curve.jpg 83k .jpg file