Train booking hall

An accidental sound sculpture created by a wierd flutter echo.

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This doesn’t appear in travel guides to Oslo, but every sound tourist should look it out if they’re in town. Here is me describing the strange acoustic, and as I walk into the middle of the ticket hall you can hear how my voice takes on a strange warbling. (The end of the audio when I walk out from the centre is the most dramatic).

A description of the sound, listen to the warble on my voice in the middle. No electronic effects applied!

Flutter echos are caused by repeated reflections arriving at regular intervals. In the graph below, you can see them as a set of clearly spaced spikes in the response to the room to a balloon burst. A warble is heard when the reflection pattern has some subtle irregularity about it. There also has to be a delay of more than about twenty-milliseconds for the brain to sense a temporal fluttering.

A balloon burst in the railway booking hall.
A balloon burst in the booking hall.

The architect Arne Eggen kindly sent me an article about the station that includes a plan for the ticket hall. The red lines are added by me to show that the inside space isn’t a simple cylinder but two half cylinders of different radii joined together. This means focussed reflections from the top half-cylinder arrive quicker than those from the bottom half-cylinder. But it is actually more complicated than that, because the domed roof also plays a role in breaking up the regular reflections.

The other thing I learnt from the architect was it wasn’t deliberate. And the railway company didn’t like the effect when it was first built. However, once musicians and others started visiting the remarkable acoustic as a tourist attraction, the train company grew to love it and put a plaque on the floor that says ‘Akustik Skulptur.’

Location

Map. Henrik Ibsens gate, 0010 Oslo, Norway

Author: Trevor Cox

I am a Professor of Acoustic Engineering at the University of Salford where I carry out research and teaching focussing on architectural acoustics, signal processing and audio perception. I am also an author and radio broadcaster having presented many documentaries on BBC radio and written books for academics and the general public.