Absorber sizing
Porous absorber thickness and perforated-panel resonator tuning for a target frequency.
Porous absorber (mineral wool, foam)
Hz
- Thickness for good absorption (λ/4)
- 0.686429m
- Thickness for useful absorption (λ/10)
- 0.274572m
Porous material absorbs where air velocity is high: about a quarter wavelength from a hard wall. Leaving an air gap behind the panel extends the effective range downward.
Perforated panel resonator
mm
mm
mm
mm
- Open area
- 3.14159%
- Resonance frequency
- 456.409Hz
Estimate for an unfilled cavity. Mineral wool in the cavity broadens and lowers the absorption peak.
How it works
Porous absorbers work best when their thickness approaches a quarter of the wavelength, which means very thick treatment for low bass. Resonant absorbers such as perforated panels trade bandwidth for the ability to target a specific frequency within a shallow depth.
Formulas
- d ≈ λ / 4 = c / (4 f)
- f₀ = c/2π · √( P / ( D · (t + 0.8 d) ) )
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