Relates other horn (newer work):
– https://www.printables.com/model/430600-spherical-wave-horn-generator

This is a generator for horns with tractrix crossection.

Those are not the same as spherical wave horns. See here: https://www.grc.com/acoustics/an-introduction-to-horn-theory.pdf
https://audioxpress.com/page/audioXpress-Supplementary-Material

under: Horn Theory: An Introduction, Part 1 https://audioxpress.com/assets/upload/files/kolbrek2884.pdf

and: Horn Theory: An Introduction, Part 2 https://audioxpress.com/assets/upload/files/kolbrek2885.pdf

Horns act as acoustic impedance matching transformators, transformating high pressure low speed to low pressure high speed sound waves or vice versa.

Note that the sizes that are printable on common personal 3D printers are only suitable for rather high frequencies (even for whistles).
Well as it turns out low frequencies get amplified as well.
See: http://www.thingiverse.com/thing:389700

Example horn:
cutoff frequency: 4500Hz
inlet inner diameter: 20mm
inlet outer diameter: 24mm
inlet pipe length: 5mm
horn length cropped to: 80%
cropped horn mouth diameter: 126.5mm
complete horn length: 129.9mm
tractrix segment length: 124.9mm

Known issues:

For now keep crop factor >0.9 in customizer

known problem: thingiverse customizer can't deal with this file :(
found out: crop factor above 0.9000 works

Category: Audio