Acoustic Impedance

When sound crosses a boundary between two media, some energy reflects and some transmits. Explore reflection, transmission, and impedance matching.

Transmission Line — Pressure Standing Wave

Reflection coefficient R: -- | Transmission T: --

SWR: -- | Power reflected: --%

Impedance Mismatch

Normalized impedance z = Z/Z₁. The circle shows the reflection magnitude. Perfect match (z=1) → R=0. Open end (Z₂→∞) → R=+1. Closed end (Z₂=0) → R=−1.

Parameters

Medium 1 impedance Z₁: 415 Pa·s/m

Medium 2 impedance Z₂: 1500000 Pa·s/m

Frequency: 1000 Hz Tube length (wavelengths): 1.0

Z = ρ·c | R = (Z₂−Z₁)/(Z₂+Z₁) | T = 2Z₂/(Z₂+Z₁)
|R|² + (Z₁/Z₂)|T|² = 1 (energy conservation)

Acoustic impedance Z = ρc (kg/m²/s). Air: ~415 Ra. Water: ~1.5 MRa. Tissue: ~1.6 MRa. The large air–tissue mismatch explains why ~99.9% of sound is reflected at a water surface, and why ultrasound gel is needed in medical imaging.