Imam Mosque echo

Tour guides delight in standing underneath the dome and flicking a piece of paper, which creates a short, sharp “clack, clack, clack, . . .”

This Mosque was completed in 1629, in the last year of the reign of Shah Abbas. Sound bounces back and forth between the floor and ceiling, with the vast dome focusing the sound, forcing it to keep moving back and forth in a regimented fashion. Without a dome, the echo from the ceiling would be lost among all the other sound reflections in the mosque. The iconic blue-tiled mosaic tiles help to provide strong reflections, which is why so many repeats of the echo are heard.

A domed room focusing sound
You can also excite the echo by stamping your feet

Location

Esfahan’s main square

Credits

Photo: seier+seier

Mapparium

A spherical room that allows you to whisper sweet nothings in your ear!

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The Mapparium is a giant hollow globe of the world, with the seas and continents vividly drawn on stained glass. It was built in 1935 following a suggestion by architect Chester Lindsay Churchill. It took eight
months to paint and bake all 608 glass panels, which are mounted on a spherical bronze frame.

You traverse a walkway cutting through the center of the Earth linking up two opposite points on the equator. Three hundred lightbulbs illuminate the globe from the outside. Looking at the world from the inside out is an odd experience, but what also strikes visitors are the strange acoustics, which were an accidental by-product of the geometry.

One of the effects you’ll hear is false localisation:

“Suppose you are on the Mapparium bridge facing South America. There is a source of noise to your right, but you discover that you hear the noise coming from your left!”

William Hartmann, Michigan State University

This happens because the reflections from the globe are focussed and very loud. Your brain thinks the sound is coming from the reflection direction and not direct from the source. This focussing also allows you to do things like whisper in your own ear!

As you approach the exact center of the Mapparium sphere you suddenly become aware of strong reflections of your own voice . . . If you sway to the left, you hear yourself in your right ear. If you sway to the right, you hear yourself in your left ear.

William Hartmann, Michigan State University

Location

Marky Baker Eddy Library in Washington. They have regular tours. At the end of my tour, they allowed us to linger a little to play with the acoustics.

Credits

Photo: Smart Destinations

Tilted Spheres

Richard Serra’s giant concave artworks can produce an astonishing diversity of sounds.

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I stumbled across this Richard Serra sculpture when flying back from Tononto Airport. Clapping is one way of exploring the space, it’s like having a giant sound-effects unit to play with. Get the right place, and the focused reflections from the arcs follow repetative patterns creating Gatling gun echoes.

The start of this video nicely shows off the effects of clapping

It’s also fun to listen out for people with noisy roller suitcases walking down the middle. What’s nice about this sculpture is being outside a gallery means the public can play with the sound. Here is a spot of impromptu singing exploiting the acoustic.

Location

Pearson Airport. Terminal 1, after security, International departures, hammerhead F.

Credits

Photo: By Ken Mist from Brampton, Canada – Tilted Spheres, CC BY-SA 2.0

Elogio del Horizonte

This large sculpture plays with the sound of the wind and waves.

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If you stand in the center of the structure, the sound of the wind and the waves at the bottom of the cliff are intensified. The experience makes you feel as though the elements are swirling around your head.

Expedia travel guide

Created by Basque artist Eduardo Chillida, this curved concrete sculpture creates a clear and strong amplification of the sounds of the sea crashing at the bottom of the cliff. You have to stand in the center of the sculpture. Close your eyes, you will hear the noise of the waves breaking against the rocks, but the sound comes from the upper area of ​​the sculpture. Apparently it is an accidental sound scuplture, with the artist being surprised when he first heard it.

Thanks to J.Oscar for providing some first hand experience of what is going on (see first comment). It’s a reflection from the underneath of the upper ring. But the other key acoustic element is the lack of any sound straight from the breaking waves to your ear because the edge of the cliff is in the way. This lack of direct sound is what causes the image to falsely appear to come from above, and also why you’re surprised to suddenly hear the sea as you walk into the focus point.

Does anyone have recordings?

Location

The scultpute can be found in the grassy Parque del Cerro de Santa Catalina, at the top of Cimavilla, Gijón.

Credits

Photo: By Triplecaña – Own work, CC BY-SA 4.0

Site suggested by Santiago Álvarez-Buylla

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

Ear of Dionysius, Sicily

Legend has it that the funnel shape of this cavern allowed the whispers of prisioners be overheard.

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This large limestone cave has a great sound legend attached to it. The story goes that the tyrant Dionysius (ca. 432–367 BC) used this place as a prison. The wedge shape of the cavern caused peoples’ conversations to be focussed and amplified at the roof of the cave, 22m above the floor. Supposedly this enabled guards to spy on prisoners by listening to the amplified sound through a small hidden opening at the top of the cave: even when the prisoners spoke in whispers.

“The tearing of a piece of paper makes a noise not unlike that occasioned by knocking a heavy stick against a stone” Conrad Malte-Brun, 1829.

Unfortunately, it’s no longer possible to hear the effect because of safety fears; in the past travellers were hosted up by rope and pulley to the opening. Consequently, a modern listener is just left to enjoy the reverberance at ground level, marvel at the legend and take in the cavern’s ear-like shape.

Gino Iannace and collaborators [1] have made measurements and test whether the spying myth is true. Rather disappointing, they found that any whispered conversations were unintelligible and lost in a blur of reverberation. The sound sample at the top of the page was reconstructed from their measurements. Even with carefully enunciated speech, it is hard to understand what is being said.

This video has good sound, but for some reason has been shot on its side.

Logistics

The Parco Archeologico della Neapolis, which includes the cavern, also has a Greek amphitheatre which sound tourists can admire.

Credits

  • Site suggested by Nick Antonio
  • [1] G. Iannace, L. Marletta, F. Sicurella and E. Ianniello, “Acoustic measurements in the Ear of Dionysius at Syracuse (Italy)” Internoise 2010.
  • Photo: Michael Wilson (c) some rights reserved

Gol Gumbaz Mausoleum

There’s crazy acoustics in this mausoleum: a whispering gallery and also an echo chamber..

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This vast 17th century mausoleum includes the second largest dome of its type in the World, but the acoustics are even more impressive. Getting to the whispering gallery underneath the dome involves climbing a hundred or so steep, crumbly steps. If you go early enough in the day when it’s not too busy, then you can test the whispering gallery. Sound hugs the inside of the dome so a whisper can be heard nearly 40m away on the other side of the gallery.

However, if you get to this place after the crowds have arrived then the soundscape isn’t so serene. Indeed downstairs, it’s more like a municipal swimming pool during a kids’ float session. They’ll be endless whooping and shouting as visitors test out the echo. The repeating echo in this building is unusual and well worth seeking out by sound tourists. Sound keeps bouncing around the dome, so that every 3 or 4 times seconds the sound whizzes past your ear. At quiet times, this repeating echo can be heard 7-10 times before it becomes inaudible.

Location

In Vijayapura, you need to arrive early if you don’t want to be deafened by a cacophony of mass acoustic-induced hysteria.

Credits

  1. Photo: Ashwatham
  2. Sound © Audio Ease. Thanks to Arjen from Audio Ease.

Whispering Arch, Grand Central Station

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.

Sources

  • Site suggested by Charlie Mydlarz
  • Photo Nick Gray

Whispering Gallery, St Paul`s Cathedral

One of the most famous whispering galleries.

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St Paul’s Cathedral is an iconic building in the centre of London. High up in the central dome is a Whispering Gallery, which I remember visiting as a child. Climb 259 steps inside the dome, stand on one side of the circular gallery and talk very quietly and your speech can be heard quite clearly on the other side some 30m away.

St Paul’s is a circular whispering gallery. In this case, sound hugs the walls, allowing it to move from one side of the room to another without getting a lot quieter – the diagram shows some of the paths that the whispers take around the perimeter of the gallery.

Diagram showing sound in a circular whispering gallery
Sound paths in a circular whispering gallery

Location and Logistics

St Paul’s Cathedral, St Paul’s Churchyard, London, EC4M 8AD.  It’s worth arriving early in the morning and going straight to the Dome, because once the space gets busy it’s hard to pick out the whispering gallery effect amongst the hubbub.

Credits

[*] Picture Nanonic Creative Commons Attribution 2.0 License

Sound Mirrors

Acoustic mirrors were an attempt to detect enemy aircraft flying towards England in the early twentieth century.

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These amazing structures are sound mirrors. Concrete concave dishes designed to capture the sound of incoming enemy aircraft as they flew over the north sea and the channel towards England.  Acting on sound like a concave shaving mirror focusses light, the sound from the aircraft is concentrated to a point where a microphone picks up the sound.  The largest structures allowed aircraft to be detected 6.5 miles away, as well as determing the direction of attack to an accuracy of 1.5 degrees [4]. Overall they were not terribly effective, however, and became obsolete and abandoned when RADAR was invented.

Sound mirror
Sound mirror, Kilsnea, Yorkshire {1}. The focussing point where the sound is concentrated is at the top of the metal pole.

At Kilnsea, Yorkshire, UK the mirror is about 4.5m high. It was used in World War I to try and pick up the engine noise from Zeplin aircraft. This gave 3-4 minutes of extra warning before attack [2]. Zeppelins raided the North East of England fifteen times between 1915 and 1917.

Sound mirrors denge
3 Sound mirrors, Denge {3}

At Denge, Kent, UK there are three mirrors. The various acoustic mirrors were constructed in the 1920s & 1930s. The different designs are evidence of experimentation to discover which shape and size worked best. There are a 6m concrete concave mirror, a 9m hemispherical bowl and a curved 60m long mirror.

Logistics

Easy to visit

Abbot's cliff sound mirror {6}
Abbot’s cliff sound mirror {6}

1. Abbot’s Cliff, Kent, UK: grid reference TR27083867. A ten minute walk from the Folkestone – Dover road along a tarmac path [5].

Sound mirror at Hythe [6]
Sound mirror at Hythe {6}

2. The Roughs near Hythe, Kent, UK are on MoD property but several websites say the dishes can be visited. The picture is of a 9m mirror, a smaller 6m mirror lies nearby on its face [5].

3. The Redcar sound mirror is in a modern housing estate at the junction of Holyhead Drive and Greenstones Road.

Sound mirror Sunderland
Sound mirror Sunderland {8}

4. In Sunderland alongside a bridleway about 200 metres west off the Newcastle Road, Fulwell.

On private land and probably only viewable from a distance

1. Boulby, Yorkshire, UK: West of Boulby Barns Cottage on Boulby Bank. On private land, although the rear of the mirror is visible from a nearby minor road [5].

2. Kilnsea, Yorkshire, UK: Not far from a road but on private land.

3. Il Widna (“The Ear”), Malta: On private land but can be seen from a distance through a fence [5]. Large curved strip mirror similar to the large device at Denge.

Accessible only on a guided tour

Denge, near Dungeness, Kent, UK. These are not accessible to the public except via guided walks by. [5]

Sources & Links

Website dedicated to sound mirrors

[1] Photo Paul Glazzard, Creative Commons Attribution-ShareAlike 2.0 license.

[2] http://www.bbc.co.uk/humber/content/articles/2008/10/15/kilnseaabandoned_feature.shtml

[3] Photo Paul Russon, Creative Commons Attribution-ShareAlike 2.0 license.

[4] http://www.southdown-amateur-radio-society.org.uk/HTML/Soundmirrors.html

[5] http://www.andrewgrantham.co.uk/soundmirrors/

[6] Abbot’s Cliff and  Hythe photos Between a Rock, Creative Commons Attribution License.

[7] Redcarr photo © Copyright Mick Garratt and licensed for reuse under this Creative Commons Licence.

[8] Sunderland sound mirror photo, Phil Thirkell, Creative Commons License Attribution-Non-Commercial 2.0 Generic.