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).
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.
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.’
A beautiful reverb surrounded by vivid and explicit frescos.
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This doesn’t appear very high on lists of tourist attractions in Oslo, but it deserves to be much better known. It was built in 1926 by the artist Emanuel Vigeland as a gallery. Luckily, for sound tourists the windows were later filled in when it was turned into the artist’s mausoleum. Every surface in the room is now concrete or stone, and this means the sound bounces and rings around the room for an extraordinary long time. Norwegian acoustician and composer Tor Halmrast describes it as the most reverberant place for its size that he had ever experienced. When I sang a few notes, the notes hung in the air for 10-15 seconds. I can see why musicians like to perform there, because the reverb is very rich and seems to gradually cascade down from the ceiling.
Here is a simple balloon burst I recorded:
An acoustic analysis of the balloon burst and the acoustics can be found here.
The room is more dimly lit than the photo above shows, but after a while once your eyes have adapted to the dark you start to pick out the frescos covering the walls and ceiling that depict conception, life and death in very explicitly. One of the most famous mural is above the door just above the urn holding the artist’s ashes. A plume of babies rise above a pair of skeletons reclining in the missionary position.