// Acoustic calculator

Horn
Sizing

Pick a cutoff frequency and throat size to get dimensions for a round-mouth exponential horn.

Cutoff Frequency Hz
20 80 320 1.3k 5.1k 20k
Throat Diameter 33.0 cm
Expansion 17:1
// Results Round mouth · Exponential
Wavelength 429 cm ≈ 4.29 m
Horn Length 96.9 cm
Mouth Diameter 136 cm ≈ 1.36 m
Mouth Area 14,628 cm² ≈ 1.46 m²

// How it's calculated

  • —Mouth: sized so ka = 1 at cutoff (d = λ/π). This is the minimum radius at which a circular opening radiates efficiently rather than reflecting energy back.
  • —Horn length: L = ln(Smouth / Sthroat) / m, where m = 4πf/c is the exponential flare rate at cutoff. This is the exact acoustic path length for the expansion to occur.
  • —Speed of sound: 343 m/s (dry air, ~20 °C).

// Rectangular mouths

  • —Sizing: use W × H ≥ mouth area shown above.
  • —Loading: the smaller dimension limits low-frequency loading, not the area.
  • —Directivity: horizontal and vertical dispersion differ — wider mouth narrows horizontal coverage.
  • —Diffraction: sharp corners add coloration; rounding them helps.