Cave Soundscapes and Acoustics
Caves are remarkable acoustic spaces. The high humidity and limestone walls produce long reverberation times; the absence of ambient noise allows quiet sounds to carry. Several caves have been used for music — the Concert Hall at Postojna, the Cathedral chamber at Carlsbad — for exactly these reasons.
Reverberation time
Reverb time (RT60) — the time for a sound to drop 60 decibels — is the standard acoustic measure. Concert halls aim for around 2 seconds. Cave chambers regularly reach 5-15 seconds in large spaces. The Concert Hall at Postojna has RT60 around 8 seconds.
Dripping water as music
A single water drop falling in a still cave makes a clear, musical note. Multiple drips create rhythmic patterns. The acoustic resonance of cave chambers amplifies and sustains these notes. Many cavers describe wild caves as having "music" from the random combination of drips.
Infrasound
Caves with airflow generate infrasound — low-frequency vibrations below human hearing (<20 Hz). The phenomenon is documented in many large cave systems and may explain the sense of unease some people report in caves.
Concerts in caves
Postojna's Concert Hall hosts orchestral performances annually. Eisriesenwelt has hosted small recitals. Wieliczka Salt Mine in Poland has a chapel with extraordinary acoustics. The pre- human Palaeolithic use of decorated caves may have included sound — researchers have noted that the most decorated chambers in some caves are also the most acoustically resonant.
Recording
Cave recording requires careful microphone placement and very low noise floors. The Sennheiser MKH series and Schoeps CMC are common professional choices. The acoustic detail captured is unlike any surface environment.
Audible cave life
Cricket calls in cave entrances; bat squeaks at high frequencies (some audible to humans, most ultrasonic); the occasional splash from cave fish. Listening is part of cave exploration.
Explore on the map
See acoustic caves on the interactive map.