At 02:00 this Tuesday, while the rest of the city slept, a team of Year 13 students from the [SCI-PHY] Physical Sciences track stood in the centre of the Turku Cathedral nave, holding their breath.
They were not there for prayer, but for physics.
This expedition marked the commencement of the Autumn Term’s advanced module on Wave Dynamics and Architectural Acoustics. Led by Dr. Hans Weber, the students were tasked with creating a high-resolution “acoustic fingerprint” of Finland’s most significant medieval structure, determining its Reverberation Time (RT60) and Speech Transmission Index (STI).
The Challenge of Silence
The experiment required absolute silence to measure how sound decays within the massive brick vaults. This necessitated a nocturnal lockout, granted by the cathedral dean. The students set up an omnidirectional dodecahedron speaker array and a series of calibrated measurement microphones at key coordinates along the aisle.
However, the “silence” of a city is deceptive.
“We encountered a massive variable we hadn’t modeled in the classroom,” explained Sofia Petrov, the student lead for data acquisition. “The spectral analyser was showing a persistent spike at 50Hz. It was the ‘mains hum’ from the cathedral’s own electrical grid, likely radiating from the old wiring in the floor. It was masking our low-frequency decay data.”
The ‘Boiler’ Crisis
The situation was further complicated at 03:15. Just as the team was calibrating the sine-sweep signal, the cathedral’s automated district heating system cycled on.
“The pipes started clicking and hissing like a percussion section,” Dr. Weber noted. “In a laboratory, you simply turn off the noise. In a national monument, you cannot just locate a breaker box and cut the power. The students had to think fast. They realised they couldn’t stop the noise, so they had to mathematically filter it out.”
Working on laptops balanced on the pews, the students wrote a custom ‘Notch Filter’ script in Python to isolate and subtract the specific frequencies of the heating system from their recordings. It was a high-pressure exercise in real-time signal processing that no textbook could simulate.
Medieval Engineering Genius
Once the data was cleaned, the results were revealing. The analysis showed that the cathedral’s acoustic profile is specifically tuned to the frequency range of the male baritone voice (approx. 100-400Hz). While footsteps and door slams are dampened, the spoken word carries with remarkable clarity to the back of the nave.
“We assume medieval architects were just stacking bricks,” Sofia remarked. “But the data proves they had an intuitive understanding of resonance. They built a natural amplifier for the sermon.”
Final Output
The data gathered will be used to create a digital “Convolution Reverb” plugin, which will be shared with the [ART-DES] and Music departments. This will allow students to digitally place their compositions “inside” the virtual acoustic space of the cathedral, bridging the gap between 13th-century masonry and 21st-century audio engineering.
As the sun rose over the Aura River, the exhausted team packed away their cables, having successfully translated the invisible geometry of history into hard data.
Leave a Reply