This sound effect was discovered when “a workman dropped a hammer on one side of the arch and a painter on the other side, nearly 40 feet away heard him.”
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The whispering arch is a treat, talk towards the wall and someone 20 yards away can plainly hear you. pretty cool.
Aquariuz, Trip Advisor
The whispering arch is the structure to the left in the old postcard, there’s a plaque marking the spot. This whispering arch dates back to when the building was a large railway station in the nineteenth century. When someone talks into the wall, you can get sound that stays close to the edge of the arched ceiling. A classic way of illustrating this is to consider sound as a snooker ball bouncing around the edge of a circular table.
In the lobby of the St. Louis Union Station Hotel. Head for the stained Tiffany glass window featuring three robed women figures.
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.’
This railway tunnel creates an extraordinary metallic flutter.
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This old railway tunnel near Sheffield creates an extraordinary metallic flutter when you shout or clap your hands. I was alerted to this strange acoustic when I was interviewed for the Channel 5 programme Walking Britain’s Lost Railways. While many tunnels have lots of reverb, it’s unusual to have such a warbling effect.
The warble is a type of flutter echo, caused by repetitive reflection paths. The animation shows sound being modelled as a simple bouncing ball. At each wall the ball follows the law of reflection (angle of incidence = angle of reflection). The source is the black circle and the red circle is where the listener is. You can see that the sound keeps returning to the receiver, but it takes a few reflections before it returns. There is a pattern of regular reflection arrivals, but the bowed shape of the tunnel creates paths that traverse the width more than once before returning to the receiver. There’s a slightly longer explanation on my acoustical engineering blog.
If you want to experience it yourself, it’s open as part of the National Cycle Network. The tunnel is here.
A whispering gallery found in a surprising place, Grand Central Terminal in New York.
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There’s an area under 4 archways, on the way down to the lower concourse, where you can experience an amazing sound effect. If you and a friend stand at opposite ends of the underpass and one of you speaks towards the wall at a normal volume, the other person can hear you perfectly even though you are a good 10 metres away and facing in the opposite direction. The stone walls and ceiling do a great job of reflecting the sound on a path across to the opposite side of the underpass. For more on the cause of this effect, see Whispering Gallery in St Paul’s Cathedral.
Logistics and location
In the lower concourse outside the Oyster bar. Whispering galleries need to be visited when it isn’t too busy otherwise the effect can’t be heard above other noise.