Porous Absorber Calculator

Model an absorption-coefficient-vs-frequency curve from flow resistivity, thickness, and air gap using the Delany-Bazley-Miki model.

Delany-Bazley-Miki porous absorber model — flow resistivity, thickness, and an optional air gap behind the material.

Absorber thickness5cm
Air gap behind absorber0cm
Material · flow resistivity σ
Pa·s/m²
Absorption vs. frequencyNRC ≈ 0.70

How the Model Works

The Delany-Bazley-Miki model predicts a porous material's characteristic impedance and complex wavenumber from a single measured property: flow resistivity. From those, a transmission-line transform through the layer (optionally over an air gap) to the rigid wall behind it gives the surface impedance, and from that, the absorption coefficient at any frequency.

  • Flow resistivity (σ): higher values mean denser, stiffer material — light fiberglass and rigid mineral wool sit at very different points on the same absorption curve.
  • Thickness: thicker absorbers push the useful absorption band lower in frequency.
  • Air gap: spacing the absorber off the wall extends low-frequency performance without adding material.

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