Exponential Horn

For an outdoor recording project I wanted a small offset exponential horn that transitioned from round to square. The round end connects to a 9.7mm OD round electret mic (PUI Audio AOM-5024L-HD-R) and the other end matches a square opening in an enclosure.

You may notice it is not axially symmetric: the small round end is offset from the centerline, so I can mount it horizontal but with the mic element towards the top. That way any rain that might come in the open end would tend to run down and away from the mic.

Initial testing shows this horn is highly directional in the 1 kHz to 5 kHz range, with maybe +18 dB gain (rough guess 20 degree beamwidth?) relative to the same element used bare with no horn, based on measuring noise of crickets near 2 kHz. At low frequencies, of course it rolls off to no relative gain.

It may be a bit tricky to print due to the low, nearly horizontal slope on two sides near the base, but I managed it. The interior did have a bunch of stringy thr