Notre Dame has risen again, and with it, its acoustics. The iconic Paris cathedral, which suffered a devastating fire in 2019, is set to welcome visitors once more on December 8. In the wake of the blaze, acoustics expert Brian Katz has been meticulously studying the sonic characteristics of the cathedral, including the echoes and reverberations that define the space, both post-restoration and across different periods in its long history (SN: 1/12/20).

Prior to the fire, Notre Dame was known for its reverberant qualities, where sounds lingered in the air for several seconds before fading away, a result of sound waves reflecting off the walls, floor, and other surfaces within the vast interior. This reverberance was significantly diminished by the fire, which left gaping holes in the vaulted ceiling and debris scattered across the floor. Now, following extensive repairs and thorough cleaning to remove hazardous lead and other contaminants, the cathedral is closer to its former glory. However, even minor alterations to a space, such as changes in wall hangings, carpeting, or furniture, can impact its acoustics.

Science News had the opportunity to speak with Katz, who is affiliated with CNRS and Sorbonne University in Paris, about his ongoing research and what he anticipates the revitalized cathedral will sound like. This interview has been condensed and clarified for brevity.

SN: What are the current acoustics like at Notre Dame?

Katz: We conducted some preliminary measurements in late September, though much of the site was still under construction. Given the significant cleanup efforts since then, we are eager to return in the coming weeks to assess the current state. Early feedback from those who have recently visited suggests a notably reverberant environment. We anticipate it will be more so than before the fire, as the space is now exceptionally clean and refinished. Every surface was treated with latex, which not only removed lead but also all other dust and debris, resulting in a remarkably vibrant soundscape.

SN: What defines good acoustics in a space like Notre Dame?

Katz: For sermons, the cathedral has been equipped with an upgraded sound system designed to minimize sound dispersion and focus on the audience, enhancing clarity even in a reverberant space. For performers, it largely depends on the musical style and the desired reverberation. Ideally, I would love to see a system that allows for variable acoustics, such as rolling tapestries in and out to adjust the reverberance while maintaining the aesthetic. This would be the ultimate solution.

SN: How were acoustics considered during the renovation?

Katz: Once the decision was made to restore the cathedral to its pre-fire state, much of the guesswork was eliminated. There was no need to consider the acoustic impact of major structural changes, as everything was being rebuilt as it was. The focus then shifted to smaller details like carpets and tapestries. Once the cathedral is returned to regular use, it will be a matter of fine-tuning rather than major adjustments.

SN: What is it like to see Notre Dame reopening?

Katz: It brings back vivid memories of our first visit just two months after the fire, when the site was still in the early stages of cleanup. The solitude, quietness, and the lingering smell of the fire were overpowering. Now, seeing the bright, clean, and restored interior is truly remarkable. I am eagerly looking forward to experiencing it firsthand.

An animated film by Katz and his team, celebrating the acoustics of Notre Dame, will premiere on January 24 as part of UNESCO’s Week of Sound. Titled 'Vaulted Harmonies,' the film recreates the music of various historical periods as it would have sounded in the cathedral during those eras. Additionally, Katz and colleagues have developed an audio guide, 'Notre-Dame Whispers,' available on iOS and Android, which takes listeners on a virtual tour of the cathedral’s exterior, sharing the sounds of its past.

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