# 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.

# The First Build of the mk3b2 Radial Fin Horn

Much faster than I initially thought when writing the original article and providing the corresponding sample CAD files, my mk3b2 radial fin horn was already built using my  sample CAD files intended to use for a high-end 2-way speaker project. Of course, I feel  honored when someone trusts that the theoretical investigations will prove useful in practice and invests a lot of time and financial investment in such a project. The genesis of the entire speaker project has already been documented and discussed here:

I was thankfully given permission by the owner of the new speaker system to use his own photos to write an article about the build of the speaker. But I’m essentially limiting my focus to the phase of building the mk3b2 fin horn. I would like to take the interested reader on a little mk3b2 picture journey.

Milling the parts…

The side flare elements are separate parts.

Everything complete to start assembling?

The fins as close-up.

Glueing the radial base element layers.

Glueing the side elements to the radial base elements.

A step that needs high attention and accuracy is to align the fins. Great idea!

Painting and glueing the fins and radial base elements before assembling the whole horn.

Painting and assembling of the horn.

mk3b2 fin horn.

mk3b2 fin horn.

mk3b2 fin horn.

Horn adapter glueing the layers around the 3D printed inlay. I like this idea!

mk3b2 in action.

mk3b2 in action.

mk3b2 with front loaded bass reflex unit.

mk3b2 with front loaded bass reflex unit.

mk3b2 with front loaded bass reflex unit.

high end 2-way speaker system.

high end 2-way speaker system.

What a beautiful and awesome speaker system! I would like to congratulate the designers and builders on this great speaker project.

A personal comment from my side about the mk3b2 fin horn based on the previous simulations and the initial sound descriptions. I am convinced that from now on the quite well known fin horns like TH4001 and Yuichi are obsolete. They neither load sufficiently being way too short to be able to load down to their designated cut-off values nor they cannot completely avoid waist banding and especially finger printing at HF. In my opinion the mk3b2 radial fin horn is the new reference.

# The mk3b2 Radial Fin Horn

It is already some time ago when I worked together with DonVK and fluid investigating fin horns and especially finding methods how to simulate them properly with BEM. First, off I would like to mention that this collaboration was one of my highlight “diy” experiences. When three people with their respective strengths work together in a concentrated and constructive manner over a longer period of time this is a very good chance creating something special. It all started exploring the original Yuichi/Arai fin horn design and how to simulate it with BEM.

I had started developing my own fin horns already a few years before, but struggled to simulate these horns accordingly. Especially the individual fins or separate channels and their integration as BEM model at throat and at the end of the fins is tricky. You could either simulate them as individual channels but in this case several interfaces are necessary and you could end up with interface issues (one to many and many to one subdomain). Or the BEM model is one single mesh including the fins but then at fin start and end you encounter very close vertices when the fins are very sharp which is a problem with BEM. At that time more questions than answers left for me and these initial designs ended up in the drawer.