Gloucester cathedral whispering gallery

The whispering gallery (or tunnel) runs behind the magnificant Great East Window

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Doubt not but God who sits on high,

Thy secret prayers can hear;

When a dead wall thus cunningly

Conveys soft whispers to the ear.

Plaque in the gallery

Classic whispering galleries usually have obvious curved surfaces to allow sound to travel long distances without getting too quiet. This isn’t what is happening here. As the video shows you have a tunnel within which the sound can’t escape, and so travels easily from one side of the cathedral to the other.

Great demo of the whispering gallery

The first documentation of this comes a meeting of the Royal Society in 1662. Such scientific luminaries as Robert Boyle (a founder of modern chemistry) had been discussing echoes and sounds and sought further information about the whispering gallery from politician Henry Powle.

Logistics

See Gloucester Cathedral website. While you’re there, you can also enjoy the reverberation in this huge cathedral (reverberation time about 8 seconds apparently).

Photo Credits

© Julian P Guffogg (Creative Commons Licence)

Thurgoland railway tunnel

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.

Listen to the warble in the Thurgoland Tunnel

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.

A simple ray tracing in the Thurgoland Tunnel

Logistics

If you want to experience it yourself, it’s open as part of the National Cycle Network. The tunnel is here.

Credits

Photo Dave Pickersgill under this Creative Commons Licence.

Greenwich Foot Tunnel

Startling distortions of footsteps and voices in this incredibly atmospheric foot tunnel.

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Is it just me, or is it virtually impossible to resist the urge to shout and whoop when you’re in a tunnel? I’ve noticed that some tunnels work better than others, and this one under the Thames near Greenwich, London is remarkably effective. A study by artist Peter Cusack found this soundscape to be one of London’s favourite sounds [1]. The sound qualities mentioned in the study included the amazingly long reverberance and echoes as well as the acoustic distortions to familiar sounds such as footsteps and voices.

The hard tiled surfaces allow the sound to rattle back and forth in the tunnel for a long time before dying away. What’s more, sound takes ages to go up and down the length of the tunnel, which leads to amazingly long echoes.

Logistics

The south end of the tunnel is at Cutty Sark Gardens, Greenwich, London. The north end is at Island Gardens. It’s open 24 hours a day, but has a hundred steps at either end.

Credits

  1. http://www.favouritelondonsounds.org/search/list.php
  2. Sound Matthias Kispert (c) some rights reserved