I do not like the construction he did but I love the picture of this horn at the sealing of some kind of bar.

http://www.minhembio.com/The_rose/122971

Will I be look as happy as this guy is after I go over my project?

This weekend I am starting to draw the sketch and the preliminary building plan for my midbass horns. I initially thought to recruit somebody who have done it to help me with plan but after consulting with a few people I feel confident that I have all necessary skills and knowledge to do the job myself. I will be posting all information at my site, whoever feel to comment or to criticize it as I go along, please do so.

The whole project is more or less clear in my mind but there are two questions with which I am not settled.

1)  Where to buy inexpensive birch plywood? There are American, Canadian, Russian and Chinese birch plywood. I would like to go with Russian – much better quality, but it got pricy nowadays. I would like to pay for ¾ sheets of 4 by 8 no more than $40-$45 in case of mass buy. If any of you know in your jurisdictions a sores to get cheap Baltic birch then let me know – I might arrange shipping. Still, I would like to get the plywood in New England and to pick up it locally

2)   The throat transition piece – I do not have a clear image how to do it. The throat will be 7” circle, then it will be a circular pipe of very low opening rate (like all hyperbolic it almost parallel in the beginning), then it will be gradual transition to triangular shape. The whole transition will take no more than a foot long and I see a very clear how it will be. What I do not know is how to make it: material, construction techniques, way to join it with the rest of the horn, etc etc etc… My leading idea to make it from concrete and while the cement did not solidify yet to place some stands in the concrete. How to mold the complex transition piece I do not know yet. I can draw it but I do not know how to make it. I will entertain any suggestions.

Can't help with the plywood source , I'd like to buy some for myself for that price . Transition piece I'd do from stacked plywood layers screwed and glued together and cut with jigsaw. The way John Hasquin built your upperbass horns .He posted the tutorial somewhere on the DIY, orr AA site. The one or two pieces when the shape changes from round to triangular would have to filed by hand. Or if you want to be really precise you could order (I think so) a ready to go pieces form Jeffrey Jackson .He built a CNC router and I don't think it would be a problem to make such project. You can make really massive throat piece that way. The connection to main horn would be a wooden collar/flange on the main horn attached to throat pieces with dowels and long screws. Regards, W

Here I would like to share some basic ideas about the skeleton of the horn. This is just a view from 50.000 feet but it will give some illustration what is brewing in my mind.

The one side of the triangular horn will be flat and will sit at level of the house sealing (attic floor). Two other sides of the triangular horn are curved. They are not continuously curved (I do not think I need to bend if for such a low frequency). They rather are a sequence of 7-12 flat panels (circle’s chords) that are mounded at different angle and by changing the angle they shape the hyperbolic curve.

Here are my more or less final circulations in metric: Hyperbolic at 0.6, Throat = 249cm (7' diameter), 45Hz, ¼ size

Since I would like to keep the proper hyperbolic curve then the bends in each curved side will be almost in logarithmic scale as hyperbolic curve changes a lot in the end of the profile. Here is some twist however. I would like to take advantage of my triangular shale and to make the first and second bendable surface to have asymmetrical bends (chords). If you look at the image then you will clearly see that chords on one side of the “bendable surfaces” are in the middle of the chord on another side. Doing this, I will increase smoothness of my opening. It will not be complicate to do it but it will be a bit pain in ass to circulate the sq area.

After a long contemplation about the material for the horn I have my leading idea of something that I call “Soft Shell Boat” approach. I did contemplated many different approaches, starting from very cheap and frugal (like most of the DIY Californians do) to very much overbuilt approach (two layers with sand between them). Considering my specific case and reasonable weight limitation on my attic I think my “Soft Shell Boat” approach will work very nice. The idea is to build an inverted boat hull with ribs outside. The Soft Shell will be most likely ¾ Russian plywood birches. Each connection between the chords will have before and after a set of ribs (brasses) made from 2x2 and 2x4 (asymmetrical). The 2x4 of the any nearby chords will be connected by 2x2 and 2x4 (asymmetrical as well).  The whole idea do not use very strong surface of the horn is to let the very massive ribs to care the load across the horn surface. If everything will go as I plane then it will be no more than one sq feet of plywood in free hanging mode.  The image below illustrates the idea for 4 chords (divisions between the chords are think black lines and the ribs are thick lines). For sake of simplicity the chords in the image are made with no angles.

Rgs, Romy the Cat

Jessie has already shared the smartest approach to the transitional shapes. The idea is to build it up or cast the weird stuff, until you get to a shape/profile you can easily work with plywood.  You will NOT want to try to make curves with 3/4" birch ply, so use this for the straight walls and lay up thin ply layers over a frame for the curves.  The price of plywood is currently at a 2-year high.  Good luck finding good 3/4" birch ply under $60/4X8 sheet.  Some birch ply will edge shatter if nails are placed too near the edges, so be mindful of that.  I recommend pre-fitting and then gluing everything in addition to nailing with ring-shank nails.

Best regards,
Paul S

Wojtek wrote:

Can't help with the plywood source , I'd like to buy some for myself for that price .

Paul S wrote:

If not, what does the shading that looks like trusses mean to show? If so, your carpenters are either very good, very optimistic or very hungry.

jessie.dazzle wrote:

From this and from the mention of 3/4" plywood, I deduce that the "curved" walls of these horns will likely be described by a series of facets (flat planes). It is said to be okay at these frequencies; this must assume a provision that the "resolution" at which the flare will be "pixelated" is not too coarse. What is too coarse? 1 or 2 planes per meter (ppm)? As the flare is more straight twoards the throat, this figure would logically vary along the flare's length. It might also be desirable to further randomize the resolution by varying the axial dimension of each plane beyond what is naturally suggested by an economy-based interpretation of the flare.