Towards the Acoustic Characterisation of Ngilgi Cave's Amphitheatre Chamber in Western Australia

Abstract Ngilgi Cave, Western Australia’s first show cave and a site of Wardandi custodianship for tens of thousands of years, has long been celebrated for its “remarkable acoustics”. This reputation is anchored in the early twentieth-century anecdote of Dame Nellie Melba singing in its Amphitheatre chamber. This paper presents a quantitative acoustic characterisation of that chamber using in situ measurements within a nominal 2500 m 3 interconnected limestone volume with dense speleothem surfaces. Room acoustic parameters were measured as per ISO 3382–1 across four receiver positions spanning 1–15 m from the source. Spatially-averaged mid-frequency Reverberation Time was 1.2 s, Early Decay Time was 1.2 s, Clarity Indices for speech and music were 0.1 dB and –4.6 dB, respectively, and Definition was 0.26. These parameter values are comparable to those reported for similar caves and indicate acceptable musical clarity and reverberance for the audience. Stage acoustics parameters ( ST early = − 9.6 dB and ST late = − 13.2 dB ) indicate good overall acoustic impression and playing conditions for musicians. These findings are interpreted in relation to the cave’s historical performance narratives and contemporary use and are contextualised within the small but growing international body of cave acoustics research.