Sound science at Notre Dame

This exercise is a part of Educator Guide: Saving Notre Dame’s Sound / View Guide

Directions for teachers: After your students read “Saving Notre Dame’s sound,” ask them to answer the following questions. Questions are organized by subsection with general questions at the top — in case you want to divvy up the reading among students. Note: You may want to show students acoustician Brian Katz’s virtual reality simulation of a concert in Notre Dame that re-creates acoustics from various locations. If viewing on a desktop, click and drag on the video to rotate the perspective. For mobile viewing, direct your students to move their phones to rotate the perspective.


1. What is Notre Dame and where is it located? What event damaged Notre Dame in 2019?

Notre Dame is a historic cathedral in Paris, France. A fire in April 2019 destroyed the cathedral’s roof and spire and damaged other parts of the church.

2. What role do acoustics researcher have in restoring Notre Dame? What field has their work put in the spotlight?

Acoustics researchers are trying to reconstruct how Notre Dame sounded before the fire, which could be used to predict how renovations may change the cathedral’s sound. The research has brought attention to the field of heritage acoustics — or the study of sound in historical buildings.

Aural history

3. What is a sound wave? What is the difference between an echo and reverberation?

A sound wave is how a sound moves through air. Sound waves are made of vibrating air molecules that cause variations in pressure. An echo is a delayed repetition of an original sound, made by sound waves bouncing off a single surface. Reverberations are created when sound waves bounce off many surfaces and can’t be distinguished individually. We perceive the sound as fading over time.

4. What is reverberation time? Name two factors that can affect a room’s reverberation time.

Reverberation time is the number of seconds it takes for a sound to fade by 60 decibels. The materials in a room and the size of the room can influence reverberation time. Rooms with marble and limestone, which tend to reflect sound waves, have longer reverberation times. It takes sound waves longer to travel between surfaces in larger rooms, which can increase reverberation time.

Sound of silence

5. What did researcher Brian Katz record in 2013 and why is this recording considered special? Describe one acoustic property that Katz measured. Why is this measurement important?

Katz took detailed measurements of Notre Dame’s acoustics. The recording is special because it is the only recording of its kind that exists. Katz measured the cathedral’s room impulse response, or how the loudness of a sound varies after it is initially made. Researchers can use the room impulse response to figure out reverberation time and other acoustic properties that affect how listeners perceive sound.

6. What path did Katz take to become an acoustician?

It’s interesting that Katz researches the physics of sound because he doesn’t play any instruments and isn’t a conventional physicist. He studied physics in college at Brandeis University in Massachusetts, but unlike his peers who were interested in the physics of the universe and cosmos, Katz was more intrigued by physics on the human scale. He eventually found his way to studying acoustics, thanks in part to setting up sound systems for events at school.

Music from ruins

7. What other buildings’ acoustics have been re-created? How do those re-creations compare with Katz’s work on Notre Dame? 

Researchers have reconstructed the acoustics of a ruined English abbey and a 16th century Italian church. The English abbey reconstruction required researchers to make a lot of assumptions because only a few walls of the abbey and its arches remained. The researchers couldn’t make detailed measurements like those at the Italian church or at Notre Dame.

8. What does the author compare to acoustic time machines? Why is the simile appropriate?

The techniques that researchers use to measure buildings’ acoustic properties are like time machines because they can transport listeners to an earlier era by re-creating how buildings sounded in the past.

The measure of a cathedral & Tuning up

9. What was Notre Dame’s average reverberation time in 2013? What characteristic of the sound affects reverberation time?

Notre Dame Cathedral has an average reverberation time of about six seconds. The reverberation time varies depending on the pitch, or how low or high a sound is.

10. How might Katz’s simulation of Notre Dame aid rebuilding efforts?

The simulation re-creates the acoustics of the cathedral and so he can use it to test how various changes to the structure or materials used could affect the real cathedral’s sound. 

Crafting a soundscape

11. Who is Mylène Paroden? How does her work complement Katz’s work?

Mylène Paroden is a soundscape archaeologist who reproduces ambient sounds of the past, including sounds that would have been heard on battlefields and on the streets of Paris outside Notre Dame. When combined with Katz’s acoustic model, the reproduced sounds can reveal what a person might hear within Notre Dame at different periods in history.

12. What does acoustician Damian Murphy mean when he says that no historic building is ever completely static? How is this relevant to Notre Dame’s rebuilding?

Murphy means that as time goes on, buildings are constantly changing. There is no single Notre Dame; it has changed a lot. Rebuilders will decide what the next Notre Dame looks and sounds like.