Cavity Resonance

Cavity resonance is a phenomenon where an enclosed volume of air acts as a resonant system, strongly amplifying sound at specific frequencies determined by the cavity's geometry. The most well-known form is Helmholtz resonance, named after Hermann von Helmholtz, where a volume connected to the exterior through a narrow opening resonates at a frequency determined by the volume size and neck dimensions — the same principle that makes a bottle "hoot" when you blow across its opening.

In professional audio environments, cavity resonances appear in many contexts. Speaker enclosures are deliberately designed to exploit cavity resonance (bass reflex ports are Helmholtz resonators tuned to extend low-frequency response). However, unintended cavities — behind wall panels, inside podiums, within ceiling voids — can create problematic resonances that color the sound and reduce measurement accuracy.

Cavity resonance in building acoustics affects sound insulation performance. Lightweight double-wall constructions (drywall on metal studs) have a mass-air-mass resonance frequency where sound transmission actually increases. This resonance, typically between 50-150 Hz, creates a dip in the sound reduction index that can compromise compliance with building codes. Filling the cavity with absorptive material (mineral wool) damps this resonance.

SonaVyx helps identify cavity resonances through several tools. The RTA reveals narrow peaks that may indicate resonant cavities. The impulse response shows ringing at the resonant frequency. The room scan estimates room modes including cavity effects. For deliberate resonator design (bass traps, Helmholtz absorbers), AcousPlan provides design calculators that predict the tuning frequency and absorption bandwidth.