Perforated Resonator Calculator

The Perforated Resonator calculator computes resonant frequency, Q factor, and absorption curve for a panel with circular holes or slots mounted in front of an air cavity with porous backing (mineral wool, polyester). The tool runs in two modes — "Perforated" (circular holes on a square grid) and "Slot" (parallel slits) — and supports three geometry-input modes: diameter + spacing, perforation ratio + spacing, perforation ratio + diameter. Why it matters: perforated panels are the middle ground between the narrowband Helmholtz resonator and the broadband porous absorber. The panel itself tunes a peak at a specific frequency (typically 100–500 Hz); the porous backing catches residual energy across a wide band. The construction is more compact than membrane absorbers (the panel does not need to vibrate), easier to install, and integrates well into interior design — often disguised as decorative perforation on ceilings or walls. How to read results: the primary tile is resonant frequency f₀ (green border); Q factor shows peak sharpness (Q < 1 — broadband, Q ≈ 2–5 — typical, Q > 30 — bare panel without backing, useless); bandwidth BW = f₀/Q reflects the -3 dB peak width. The absorption curve is normal-incidence (impedance-tube convention) — in a real room the Sabine coefficient will be 1.2–1.4× higher at resonance. Treat this as guidance, not as the exact value for RT60 calculations. Common mistakes: bare panel without porous backing — yields Q ≥ 30 and a uselessly narrow peak; perforation ratio > 20 % — the construction stops being a resonator and behaves like a porous absorber (the calculator warns); hole diameter < 1 mm — micro-perforated (MPP) regime, requires Maa formula (Phase 2); hole spacing ≤ diameter — holes physically overlap, geometry impossible. Next steps: for a problematic room mode, open the room-modes calculator, find the target frequency, switch the perforated calculator to "Design for target frequency" mode, and solve for cavity depth or perforation ratio. Compare with a Helmholtz resonator at the same frequency — the perforated panel has a wider tail, the Helmholtz has a sharper peak.