Page 57 - Summer2022

Characterization of how the Marsoulas Cave modifies sounds produced within was done using portable audio electronics (Figure 5) to make spatial impulse-response measurements. This is the standard procedure for room acoustics, where a known signal is produced from a source and recorded by microphone receivers for analysis. The sound source and receiver were located at approxi- mate human head heights in various positions within the central section of the cave. Due to prior excavations and the presence of a few metal support structures, there cannot be perfect correspondence between the extant cave interior and its conditions during Magdalenian times. However, the overall dimensions and cross-sec- tional geometries of the cave have not been modified (as evinced by the intact paintings); therefore, measured acoustical parameters and noted structural features would have been similar during the Upper Paleolithic. Impulse-response measurements are the standard tech- nique for documenting how an enclosed space reflects and absorbs acoustic energy throughout the frequency spectrum of human audition and bodily sensing. One of the most common acoustical metrics for enclosed spaces that has strong perceptual implications is reverberation time. In the Marsoulas Cave, an analysis of spatial impulse responses collected in locations near the wall art indicate short reverberation times across most of the range of human hearing, around 300 milliseconds for octave bands centered at 250 Hz (near the Marsoulas conch’s sounding tone) and above. The standard RT30 metric for reverbera- tion time (Figure 6) shows an increase in the prolongation of sound with decreasing frequency, reaching about a half-second duration in the 63-Hz centered band, below that produced by the conch and consistent with the cave’s length. Measured acoustics enable the tuning and verifica- tion of computational acoustical models, a new research direction that will be used to produce auralization dem- onstrations of the conch in its cave. Musical Acoustics for Archaeological Interpretation Archaeological interpretations are based on inferences from converging material evidence of past human activi- ties. One way to deal with mysteries in the archaeological record is to evaluate functionalities of assembled materi- als according to what can be known about where, how, and by whom they were used. Musical acoustics offers methodologies for these investigations, such as that of Figure 6. ISO-3382 room acoustics metrics (analyzed using RØDE Fuzzmeasure software) applied to impulse-response data collected at human head height in front of the central bison painting in the Marsoulas Cave as shown in Figure 5. Reverberation time ( T30) is shown, with good agreement across the four channels of the first-order Ambisonics (FOA) microphone (Zoom H3VR) that recorded the impulse responses that were generated via exponential sinusoidal sweeps through a portable omnidirectional loudspeaker (Bose Soundlink Revolve+). Values from the four cardioid outputs of the FOA microphone are plotted (colored lines) along with their average values (black line). Summer 2022 • Acoustics Today 57