Acoustic archaeologists examine pre-Inca civilisation
Published: MEA
WORLD: A microphone array isn’t the typical tool most people would associate with archaeology, but it is a vital element being used to explore the acoustic properties of a 3,000-year old ceremonial centre in Peru.
At Chavín de Huántar, a ritual centre in the Peruvian Andes, advanced processing and Countryman’s B6 precision mics are enabling acoustic archaeologists to unlock the sonic secrets of a vanished pre-Inca civilisation. Miriam Kolar, a PhD candidate at Stanford’s Computer Research in Music and Acoustics program and a recipient of a Stanford interdisciplinary graduate fellowship (SIGF), is the lead investigator for the Chavín de Huántar Archaeological Acoustics Project. She has been leading the acoustic investigation since 2008 with the goal of interpreting the project’s findings in the context of the human perception of sound.
‘Chavín de Huántar is a 3,000-year old Andean ceremonial centre that encloses a massive stone network of rooms, corridors, shafts, and drains - architecture that has remained remarkably intact since construction ended in approximately 600 BC,’ Ms Kolar explained. ‘In 2001, Stanford Archaeologist John Rick discovered 20 marine shell trumpets at the site. They were all in one location, were beautifully decorated and remain playable. This was an unprecedented discovery. Suddenly, there was a connection to the musical universe. The archaeological thought was that this site was some sort of ceremonial centre and we wanted to better comprehend the structure, its sonic character, and its impact on the sensory experience in order to better understand what may have taken place there.’
The unique microphone array developed for acoustic measurements at Chavín de Huántar consists of 16 Countryman B6 omnidirectional lavaliere microphones. ‘The B6 is tiny,’ Ms Kolar notes, ‘and when you’re making acoustic measurements, you want your equipment to be as small as possible in relation to the sound field because a small mic will alter the sound field less than a large one. With the B6, sound waves of human hearing frequencies won’t scatter, and diffract around the microphone elements. The B6’s frequency response is very flat, it’s durable and moisture resistant, and it has a unique, flexible connector that enables us to manipulate each microphone’s position. So the array, which visually resembles a bouquet of flowers, can be adjusted to measure sound waves from myriad points simultaneously.
‘The flexible stem of the B6 made these microphones the ideal tool for this type of application, and in part suggested our configurable array design led by consulting professor Jonathan S. Abel,’ she continued, ‘This stem makes it very easy to adjust the mic’s positioning - enabling us to precisely control where the individual mics are in relation to each other. To make measurements, we put multiple sound sources throughout the space and the microphone array enables us to sample the sound field at high resolution. This arrangement gives us the ability to capture the arrival direction and the strength of individual reflections, enabling an accurate digital reconstruction of the sound field.’
While the Chavín de Huántar Archaeological Acoustics project is an ongoing effort, numerous findings have already been presented at forums such as Acoustics ’08 in Paris, the Institute for Andean Studies, and AES New York 2009. ‘This project is a giant undertaking, and I’m certain there is much more to discover,’ noted Ms Kolar. ‘Countryman has been extremely supportive of our efforts and has been tremendous in terms of helping us optimise our use of the microphones. Everyone at Countryman has been extremely responsive and a pleasure to work with.’
https://ccrma.stanford.edu/groups/chavin/
http://vpge.stanford.edu/SIGF/index.html