Bacek Posted October 28, 2019 Share Posted October 28, 2019 Superelliptical tractrix horn for tweeter - a.k.a small rain from a big cloud. Why a.k.a. It took me several years to actually implement this idea and originally I was planing it for 400Hz horn. I started to think about it in Forte days, I was planing to build some external mid/high horn for fun. Then as replacement horn for La Scala. Original material suppose to be something else. Don't know English name but I was planing it as cast made of polymer resin with mineral filler. Friend of mine was doing round horns with it and I really liked the product. So as I said got idea maybe 5 or more years ago, I did math, CAD project and laid it into a drawer for a long time. Doing large horns is really challenging. Inspired by Dave A work on tweeters I thought why not try something much smaller fist. So I ended with small solid beech wood tweeter horn instead of huge cast resin one. OK so why Superellipse? It's fun curve. Special cases of this curve are circle, ellipsis and in the end rectangle. By manipulating basic curve parameters we can do smooth transition from circle to rectangle or in this specific case rectangle with rounded corners and all the way be compliant with Tractrix horn flare. Why to bother when we have elliptical horns? Because using same front area we can make horn with lower cut of frequency without having any sharp edges on wave path. So basically join elliptical and rectangle horn strong points. Of course it's not always desirable to have lowest cut of freq but in this case math looked good. I have created parameterized xls sheet witch which I can control how transition from circular throat changes to semi rectangular mouth. Horn is calculated for 1544Hz and has good loading from 4147Hz (strange tails but I was shooting for particular mouth size) For this particular horn for half of length it goes smoothly from circle to ellipsis and then shape starts to be more rectangular. But this is fluent and I could make it almost rect from the beginning. From math I did FreeCAD project (or actually my xls almost generates it). Then I had to find someone who will make wooden prototype. It's not so easy to find someone who wants to play with such "large", 4 items, orders, but finally I did. As always with prototype not everything is 100% correct so cut off is probably bit higher but as proof of concept it went well. I stained it little bit and painted with semigloss lacquer I decided to use B&C DE120 for it. Guess I was not reading too carefully because to use it I needed to scrap some wood from top hat to fit drivers magnet. I did some measurements to compare K77 square, K77 round in original horns and DE120 to mine. Looks fine. Green is round, red is square, blue is DE120. Don't pay attention for reference level, my mike has +3 or more dBa from 16kHz but as reference to other K77 measurements it's fine. Currently my system plays better then ever. Unfortunately I cannot say it's all because of horn/tweeter change. At the same same I went from passive to fully active system. So currently I'm using active digital crossover (Najda DSP) with 6 channel Rotel amp. Additionally to normal crossover points I did full time delay alignment for all drivers. With everything changed I really love to listen live recordings. For good realizations it sometimes gives me an illusion of being actually there at time of a concert. Now it's time for bass extension with La Scala bass reflex mod 2 Quote Link to comment Share on other sites More sharing options...
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