The sounds in the prayer hall have changed over the centuries.
The sounds in the prayer hall have changed over the centuries. Tim Adams/CC by 2.0

When a building is slated for an addition or a renovation, preservation-minded architects often look for ways to keep the aesthetics visually consistent. They are less likely to consider the acoustic landscape inside. In many cases, though, sounds are a key part of what makes a place feel like itself.

Recently, Rafael Suárez and collaborators at the Higher Technical School of Architecture at the University of Seville wondered what the Mosque–Cathedral of Córdoba would have sounded like thousands of years ago, during the age of Abd al-Rahman I. Construction began on the Moorish structure in the 780s. It was enlarged a few times during its life as a mosque—more naves were added to the prayer hall, and more arches soared. Then, in the Renaissance, it was renovated as a Roman Catholic church.

Unlike fragments of tools or shards of pottery, sounds don’t lodge themselves in the soil. They don’t linger. But archaeologists specializing in acoustics, also known as archaeo-acousticians, can model what particular environments may have sounded like to people who passed through long ago.

To approximate the acoustic environment of past iterations of the Mosque–Cathedral of Córdoba, Suárez and his team worked backwards. They started with a present-day measure of impulse responses around the space. They placed the source of the sound near the mihrab and minbar, where sermons were recited. (To control for other, unrelated sounds, they measured after hours, when the space was empty.) From there, they used software to reconstruct the internal architecture of the mosque during four different phases of construction and renovation. They set up receivers throughout the space, and considered the absorption or scattering effect of various surfaces. Next, they produced auralizations, or sound files replicating what worshippers would have heard.

The mihrab is richly detailed.
The mihrab is richly detailed. Jocelyn Erskine-Kellie/CC by 2.0

They describe their findings in a new paper in the journal Applied Acoustics. In the 780s configuration, the researchers found, the sound was easily intelligible from the nave all the way around the prayer room. Subsequent construction added more depth, and also moved the sermon space off-center. That led to reverberations. Later, more construction created what the authors describe as “acoustic shadow zones”—places where little direct sound arrives.

What would these changes have sounded like to worshippers? To find out, the researchers used software to model how the architecture would change the same snippet of a recorded salat, or daily prayer. In the first configuration, the prayer sounds full-bodied and sonorous; in the model that reflects the mosque’s last renovation, the same prayer echoes as though it was recited deep inside a cave.

Visually, a lot has stayed the same in Córdoba over the past 1,200 years. Gilt calligraphy and intricate tiles still decorate prayer spaces, and hundreds of columns—made from jasper, onyx, marble, and other stones salvaged from Roman ruins—continue to stand in the hypostyle hall. Sonically, it’s a different story. “The increase in area and, consequently, in the volume of the temple, has generated significant deterioration of the acoustic conditions,” the authors write. “The enlargement interventions failed to take the functional aspect of the mosque and gave the highest priority to mainly the aesthetic aspect.” Identical words, delivered today, wouldn’t sound exactly the same.