During the restoration of Notre-Dame Cathedral, a multidisciplinary team of scientists from the CNRS (National Centre for Scientific Research) and Sorbonne University collaborated closely with the restoration team to preserve and safeguard its renowned acoustics.
This effort involved detailed acoustic measurements, advanced modeling techniques, and the use of cutting-edge technology to ensure that the cathedral’s unique sound properties, integral to its historical and cultural significance, remained intact despite the extensive repairs.
Their work also included studying the impact of the restoration materials and methods on sound reflection, reverberation, and overall auditory experience within the iconic structure.
Scientists build a virtual twin of Notre-Dame to help restore its glory
Virtual model
The first step was developing a virtual model of Notre-Dame's acoustics which simulates the sound characteristics of the cathedral before the April 2019 fire. This model also provides insights into the evolution of Notre-Dame's acoustics over the centuries.
Speaking about his team’s contribution to the restoration of Notre-Dame, Brian Katz, a leading researcher specializing in architectural acoustics, explained that the acoustics team dedicated their efforts to two primary objectives: documenting the acoustic evolution of Notre-Dame throughout the reconstruction process and creating detailed models of its acoustics.
"This was to provide advice to the architecture and restoration team and to look at the acoustic impact of any suggested modifications that they wanted to do," he said.
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The documentation involved conducting precise acoustic measurements at various stages of the restoration to track changes caused by construction activities and new materials.
Simultaneously, the team developed advanced 3D computer models to simulate the cathedral's acoustic properties, enabling predictions of how alterations to its structure might affect sound propagation.
This work ensured that Notre-Dame's famed acoustical heritage, vital for music and liturgical ceremonies, would be preserved and restored accurately.
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Devasting fire
Explaining how the project began, Katz detailed the role his team played following the devastating fire at Notre-Dame in April 2019. Shortly after the tragedy, the acoustics team submitted several research proposals aimed at exploring both the cathedral’s acoustic history and its future potential
. Their goal was to investigate how the unique sound characteristics of Notre-Dame evolved over centuries and to ensure their preservation during the reconstruction process.
“When President Macron announced that the restoration would be as it was before,” Katz explained, “it freed up a lot of our efforts, research-wise, that were going to be directed to the future, to look to the past.”
This shift allowed the team to focus on studying historical records, conducting simulations based on previous architectural configurations, and utilizing pre-fire acoustic measurements to recreate and preserve the original auditory experience of the iconic cathedral.
Their work has been instrumental in aligning the restoration with the historical essence of Notre-Dame’s celebrated soundscape.
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Katz also pointed out that one of the other focuses of the project was to put some effort into communicating the results of their research to the public instead of just relying on scientific papers.
Katz and his team have developed a free, immersive audio guide called 'Notre-Dame Whispers' which is available on iPhone and Android.
"It places all of our research in a kind of a museum guide in 3D audio over headphones where you can walk around the outside of Notre-Dame and listen to parts of the history whether it's the bells or the choir or the organ or the reconstruction," he said.
