Recreating the Acoustics of Notre-Dame de Paris

To address this, the digital model of the cathedral’s acoustics developed by Brian FG Katz, a CNRS research director at the Jean le Rond d’Alembert Institute, could prove invaluable.

A Virtual Model of Acoustics

For over 30 years, the Lutheries – Acoustics – Music (LAM) team from the Jean le Rond d’Alembert Institute has conducted studies to document the unique acoustics of Notre-Dame. The first series of measurements was conducted in 1987 at the request of the Ministry of Culture to study the feasibility of building a new organ. In 2015, Brian FG Katz developed a digital model of the cathedral’s acoustics as part of the "Ghost Orchestra" project.

In partnership with the Paris Conservatory (CNSMDP), the team created a highly precise recording of the concert held in the cathedral for its 850th anniversary in 2013—an oratorio of Massenet’s La Vierge.

“We aimed to reconstruct the cathedral’s sound characteristics beyond just its geometric structure,” explains Brian FG Katz, who had previously worked on the historical reconstruction of several Parisian theaters.

Using advanced acoustic technologies, such as omnidirectional microphones and artificial heads that mimic human hearing, the team combined these measurements with architectural data to construct a virtual acoustic model of the space.

“In this model, we recreated the cathedral’s 3D architecture and assigned acoustic values to each type of surface (stone, wood, stained glass, paintings, etc.),” Katz explains. “It’s like adding colors and textures to a 3D image, but in this case, we’re adding acoustic textures.”

The result? Audiences can now experience the concert from various perspectives and enjoy an immersive experience by virtually navigating inside the 3D cathedral.

Interdisciplinary Collaboration

Creating this virtual acoustic model required close collaboration with historians, including Andrew Tallon, a specialist in Gothic architecture. Tallon’s 3D scans of Notre-Dame helped verify architectural details of the model, such as the height and curvature of the vaults.

“Acoustics is a science of detail. The shape, position, and materials of every element, from sculptures to woodwork, can influence the sound,” says Katz.

Before the fire, Notre-Dame contained numerous wooden panels and paintings. “These small elements of sound absorption and diffusion had significant effects on the cathedral’s acoustics,” the researcher adds.

A Valuable Tool for Reconstruction of the Cathedral

Thanks to this model, researchers now have a precise description of Notre-Dame’s acoustics that will aid in its reconstruction.

“With our virtual model, we can guide architects in their restoration choices by simulating the impact of different materials on the cathedral’s acoustics,” Katz emphasizes.

The importance of acoustical science in heritage restoration is well established. Katz cites the example of the Fenice Opera House in Venice, where pre-fire acoustic measurements enabled the restoration team to replicate the original sound of the venue.

Experiencing the Past and Creating New Concerts

The virtual model also enables researchers to observe the evolution of Notre-Dame’s acoustics over the centuries.

“The cathedral’s acoustics today are not the same as they were 100 or 700 years ago,” Katz notes. “In the past, there was likely less reverberation. The function of the space was entirely different. Painted walls, tapestries, wool or silk draperies, and decorative elements likely absorbed more sound.”

The acoustic model could also be used to create virtual concerts broadcast live in the digital replica of Notre-Dame.

“The Paris Conservatory has more than a dozen recordings of concerts performed at Notre-Dame that we can refine with this digital acoustic model,” Katz explains. This would allow audiences to relive the “lost” acoustics of Notre-Dame during a concert.