HF Horn/Waveguides

This is going to be part of my project in another thread. I wasn't getting very good HF response, so I'm looking into the causes and trying some other ideas.

This is one of the HF horns I was using





I tried measuring it without the rest of the box. There was a massive difference in top end when measuring on and off axis, in the long mouth direction. The best measurement was over 12 degrees off axis. Here is a comparison plot





I'm thinking the top end is bad on axis due to the bends in the middle pair of 'hornlets,' not helped by the internal width of them, it looks like there is nothing to make the shorter waves follow the contours, they would take a shortcut down the middle and cause cancellations. The outer hornlets are more straight.


To check it wasn't a problem with the overall horn dimensions and flare rate (which is fairly low,) I made a simple radial type horn with the same flare dimensions











This was measure using the same driver, settings and distance as the original horn





This looks fairly good. The trace with the dip around 15kHz was made on axis. I assume this is some sort of reflection across the straight sides of the horn. I won't be investigating any further as this horn won't actually work in the box I'm designing.

I can add a little advice to this design. No sharp edges or corners inside the waveguide. Just a small radius on every inside edge will do Wonders for you :)

Edited by FOO - 26 July 2020 at 6:36pm

doober wrote: I have been very careful to make the path lengths the same. The silicone mould will allow me to make horns with different curvatures. I can take the corners off the mould, this can be done with a knife as I shave off the little stray bits. What is the reason for not having sharp corners?

Here is the first attempt made from epoxy. It needs a bit of tidying up, and some outer walls. I'll probably just clamp it between 2 pieces of ply to give it a test. It is 2 separate casts, either side of a sheet of unclad epoxy PCB, with a GRP mounting flange and throat stuck on the end.








Hopefully I'll get to test it soon

Thanks, these techniques are new to me too, I'm making it up as I go!

I clamped it between 2 pieces of MDF and fitted a driver





This is the result, no EQ or filters





Looks like the HF is there,hopefully enough to sort out with a high-shelf EQ. It doesn't vary much off axis. I might knock up a small horn for further testing.

I made a very basic 90 degree horn and did a test




Plot with no EQ or crossover





It looks a bit smoother now, there is quite a drop towards the high end, but it is a steady drop. It takes quite a boost to make it close to flat. I'm not sure whether it is too much, and when I make the proper box it might make things worse. I plan to use 4 of these horns to make a 500mm tall slot, curved in the vertical plane, my concern is that lower frequencies will get a boost from combining, higher frequencies will spread more and become weaker.