The Lighthouse “voice” on Flat Holm

the building as a musical instrument

The lighthouse stands, inert and mute, in a wild soundscape evoked by ceaseless motion of wind and sea, ebbing and flowing with the seasons. Passing denizens – ships, aircraft and, above all, seabirds – contribute their hurried and intermittent comment. 

A hollow core inside the stone masonry leads from an entrance on the rock to the lantern, 75 or so feet above, and is protected from environmental turmoil by walls 4 feet thick with only the tiniest of windows. The stairway rising within is isolated from the rest of the world. 

But in place of the expected silence, the core generates its own distinctive sound. It is singing. Basso profundo. It has been doing so continuously for over two hundred years, heard only by the few people who have had the privilege of entering its door. 

Their journey up to the lantern would pass through this cocooned and resonant world. But then at the top, as they break out onto a circular balcony, the external soundscape would reassert itself. 

We encountered the “voice” of the lighthouse in a visit we made with engineers from Trinity House, whose job it is to maintain the light and its supporting structure and services. It was quite a windy day which, happily for us, must have augmented the voice. The continuous low-frequency boom that filled the interior was quite unexpected to us, but unmistakable. We set up a binaural head, a recording device that mimics human listening, at the foot of the stairwell and began recording. 

A spectrogram, a map of the sound frequencies in our binaural recording, reveals that the voice is an array of discrete notes blending together. These are the notes at which the column of air in the lighthouse resonates. They fall into a series, a harmonic series, whose frequencies are in simple numeric proportion. They suggest that the column of air in the lighthouse is behaving like a giant musical instrument. The lowest note of which the instrument is capable, its fundamental, can be guessed at from the spectrogram. It is certainly below the human hearing range, as are the lowest of the harmonics. As best we could tell, the lowest note is the result of air silently sloshing to and fro at the syrupy frequency of 7.5 cycles per second. Theory tells us that any 75 feet high column of air, closed at both ends, should indeed resonate at this fundamental frequency. 

To the men who kept the light burning, this continuous voice must have been protective and reassuring. To shift attention to its feminine side, we have chosen a woman’s voice to represent the building in the film Lighthouse.  Written by Glenn Davidson & Mike Fedeski.