Exponential Horns are amazing acoustical machines with no moving parts. They also look gorgeous. Here I'll show you how I made several thin-walled aluminum and steel exponential horns. They work great as loudspeakers, and (my original intent) as smoke-ring cannons aka vortex-ring cannons. Whether you've got a 1920's Victrola, or a 2014 High fidelity sound system, exponential horns like this are unbeaten as the most efficient way to spread sound from a limited source.
Acoustical Horns are Like Gears on a Bicycle
Horns are like gears for sound pressure waves, coupling forceful motions of a small quantity of air into small motions of a large quantity of air, or vis versa. They can make a loudspeaker broadcast sound more efficiently, and more directionally, and they can also make a receiving sensor like your ear or a microphone more sensitive and directional. I experimented with using an exponential horn to couple the motions of air from an 18" subwoofer to an aperture, from which swirling toroidal (or 'poloidal' if you're a nit picker) vortexes could propagate long distances as an action-at-a-distance effector for various art and educational projects I'm working on. Nothing like blasting someone's hair back at 20 feet!! You'll also see some photos of that project, including a stainless steel iris, and heavy duty servo-motor controlled pan-tilt gimbal capable of aiming all the above.
You can read more about acoustical horns here: http://en.wikipedia.org/wiki/Horn_(acoustic)
What you'll need
Generate_Exponential_Horn.m is a matlab script I wrote to generate the flattened patterns of the facets of a faceted exponential horn.
The following variables should be modified:
numfacets %default 5, the number of facets of the horn. the number of sides of the polygonal cross section
dia1 %default 43 inches, the outer diameter of the horn at the widest end
dia0 %default 3 inches
If you don't want to run or modify the code to generate your own .DXF files, you can use the ones I've attached here. (Also Vcarve .CRV and flow jet .ORD files). These files should be able to be scaled in either axis and still join together nicely, too. If it's not overwhelming, you could also message me and I might be able to run off a series of files for you.
NOTE: some post-processing of the .DXF file was helpful to make sure that all the lines are in a closed, connected, curve. If I make another horn in the near future I'll update the details here as I refresh my own recollection.
An additional method of specifying your geometry would be to use Pepakura with a CAD model of the horn. But in my innocence of CAD at the point I attempted this the first time, I found it easier to write my own geometry code in Matlab than to figure out how to get Autodesk Inventor to specify a faceted exponential horn and export the flattened facets as 2D cut patterns.
Instructables / Autodesk folks, I asked the local pittsburgh autodesk employees about generating a faceted exponential horn in Inventor then exporting the flattened sheet metal facets (as well as every Techshop Pittsburgh DC and knowledgeable patron and Inventor Instructor here) and still drew a complete blank. I'd be happy to write an instructable about that aspect if you could get me started. Message me?