Recently, I was involved in a private discussion with a guy who introduced himself as expert for home cinema setups. The topic was about a horn that could be used for a really large home cinema setup. Not what many would imagine immediately like a small room for 2-3 people. No, truly large for 10 or more people and the listening rows / seats have a third dimension in the vertical direction the more far away they are from the source. For such a setup, the horn should have very good directivity control. The person tirelessly promoted the TAD TH4003 as the ultimate solution for such setups. At that time I only knew the TH4003 horn from some pictures. But over the last years I have developed an eye for whether a horn profile meets certain requirements or not. That’s why I expressed my biggest concerns about the vertical pattern control of the TH4003. However, since I had no mesh file or STEP file of the TH4003 available at the time, no final assessment could be made. The discussion then more or less fizzled out. Some months later, a STEP file for TH4003. A few months later, a STEP file literally “fell off the back of a pssing truck” ;-), which gave me the opportunity to examine the horn more closely. I also remembered one of my first William Neile waveguides and the experiments with gentle diffraction slots and realized that I actually already had something much better in the drawer.
A Nice DIY Project Using my JMLC Inspired Horn Calculator
Recently, I got a request to help with some questions regarding the use of JMLC inspired Horn calculator. Usually, I have not much spare time to help in detail, but this time was indeed different because there was a well balance of give and take.
Adam contacted me with a very nice performance JMLC horn using PETF to optimize the profile with respect to better directivity control while greatly preserving loading. It is not as good as my WN300, but I was surprised about the results. With some minor suggestions from my side to further optimize PETF parameters, Adam worked almost without my help using his own workflow. It has been proven that my splines export function is working perfectly to create a step file and then mesh the BEM components using GmsH.
A New Coherent Radial Fin Horn
Already during the collaboration with @DonVK and @fluid regarding fin horns, I shared some initial drafts of a radial fin horn with almost equal fin path lengths with help of the semicubic parabola. Traditional fin horns have the shortcoming that the path length from outer throat to find end is shorter compared to the center path length because of the radial fin arrangement. I think that it is very important that the wave front beyond the fins sum up coherently or, so to speak, have the same phase. The mk3b2 horn tried to mitigate the issues with respect to different path lengths by a different fin arrangement, with the result that mk3b2′ performance surpass the current available fin horn designs.
Luckily, one of my other interest at that time was to investigate the Bézier algorithm and how to use it in designing horns (Bezier Curve). The result was a complete horn calculator based on Bézier curves. Besides the challenge to implement the math, I learned how to handle the algorithm and also found out that multiple Bézier points with the same coordinates can be used to emphasize certain regions, where the resulting curve should be more close to a distinct point.
In this article I will describe a new algorithm that starts with a slightly curved wave front which is the result of an optimization to fulfill the defined flare rate. So the first incremental step is more or less the same as a general exponential horn. Bézier curves are used to make the fin path lengths equal, ending up with a spherical wave front at fin end which is the theoretical optimum to radiate into a flared conical bell.