Here's my take laying out the plan. All dimensions are in cm. Divide by 2.54 for inches:

- Establish a center-point (CP) and trace an arc with radius 27.5cm for the top and bottom plates
- The arc should span 130 degrees (x: +/- 24.92, y: 11.62 from CP)
- Draw an arc of 3.9cm from CP. This is where the inner tip of the vanes will sit
- From centre to edge, the vanes are located 22 degrees, 22 degrees, and 21 degrees from each other. Don't ask me why the last one is 21 and not 22.
- Don't use degrees in your layout. It's more accurate to translate to X/Y coordinates. Mark these coordinate in relation to the CP and connect them to the CP to give center lines for vanes:
(0, 27.5)
(+/- 10.3, 25.5)
(+/- 19.1, 19.78)
(+/- 24.92, 11.62)

- Clip the apex of your fan by 0.61cm to give mouth opening of 2.6cm, OR keep trimming the apex back until you get the 2.6cm opening

The best way to ensure you get 4 identical plates is to cut a hardboard template with the above dimensions. Roughcut the actual material a little oversize and use the template and laminate bit on a router to trim.

Making the 25 degree cut on the side pieces will be tricky. I made a jig for my chop-saw and even then, it took 8 cuts to get 4 good ones. Best bet is to rough cut to 1/16" oversize and level with 80 grit on a sander.

Looking forward to hearing other suggestions on building techniques.

Gar.

• audioheritage smith horn link

Yeah I know, the damn things ain't built yet and I'm already asking what-if questions.......C

I did noticed that when I switched from my 2380A horns (90x40) to the smiths, I loss a few dBs in sensitivity and had to adjust the L-pad. No big deal as most compression drivers have over 10dB advantage over the woofer, so there's lots of room to play with in the L-pad.

In my experience, I've found it difficult to accurately apply angles on a board. Much more accurate to use a bit of tri and layout with x/y coordinates. I just translated the dimensions from the plan to the x/y coordinates.

gar.