Anechoic Chambers

A claustraphobic silence that some find unpleasant and others love.

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The anechoic chamber at the University of Salford, UK
The anechoic chamber at the University of Salford, UK

When someone talks in a full anechoic chamber, their voice sounds muffled, like your ears need to pop while in an aircraft. Some visitors find the disjoint between the visual and aural unsettling. This is a room where you can see but not hear walls. One scientific study showed that if you turn the lights out, after a while some visitors will start to have hallucinations in the chamber.

Anechoic chambers are incredibly quiet and the walls of the room don’t reflect sound. This enables acousticians to test products and sound phenomena without interference from outside noises or reflections from the walls. A well designed anechoic chamber is so quiet that no sound enters your ear canals, the only sounds you hear are generated by your own body. You might hear blood moving through your head and/or a high pitched hissing originating in the auditory nerve. But the extraordinary quiet isn’t the main reason why some visitors ask to leave the chamber. The walls, floor and ceiling are covered in absorbent wedges that mean no sound reflects back to you when you talk and this sounds impressive.

This video is the best illustration I know for how quiet the space is:

And this sound of a balloon burst is a great illustration of how the anechoic chamber stops reflections, turning the normal bang into a brief click:

Location and logistics

There are many anechoic chambers in the world, but you need to find a high quality one with an absorbing floor and very low background noise level to get the full aural experience. At Salford University, our anechoic chamber opens up during open days for public tours.

Bell Caves

What makes the echoing sound of these caves unusual, is the way the different chambers are connected together.

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The Bell Caves have a unique sound. What makes the Bell Caves unusual and worth a visit is the acoustic effect created by the connections between the chambers. As the sound moves between the large chambers along the passageways, a very distinctive reverberance is heard, as sound sloshes about from one chamber to another.

The caves were quarries which were excavated at different times in history, but it is claimed some date back to the 4th century B.C. The walls are made of beige coloured limestone.

Location

The Bell Caves are in the Beit Guvrin National Park. The park also contains a Roman amphitheatre.

Credits and sources

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.

Pisa Baptistry

The rich reverberant sound in the Baptistry of Pisa lasts an astonishingly long time, to the delight of all tourists, not just sound-ones.

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Under the dome of the Baptistry in Pisa a stunning acoustic effect can be heard. Notes sung here last so long, it’s actually possible to accompany yourself: new notes will harmonize with old ones still reverberating around. The Baptistry Guards will often demonstrate this beautiful effect.

The key to the remarkable acoustic is that there’s very little soft material about to absorb the sound. Consequently, notes rattles around the space for a long time, some suggest for over 12 seconds, before the sound dies away and becomes inaudible.

Logistics

To enjoy the wonderful acoustic arrive early before it gets too busy. Website with opening hours.

Credits

  1. Sound (c) jnbcarvalho
  2. Photo: gaspa (c) some rights reserved

Vienna Musikverein

Possibly the best and most famous concert hall for classical music.

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If you were to take a straw poll among acoustic engineers to find the best concert hall in World, then the Musikverein would come pretty close to the top: it might even top the list. It’s one of four concert halls around the World that are commonly cited as sound exemplars, with extraordinary acoustics against which all new designs are compared. Like all good concert halls, the Musikverein provide sound reflections that enrich the orchestral sound. Without these reflections, the music would sound rather thin and distant.

Scientists have spent many decades trying to unlock the secrets of the hall, and perhaps the most important feature is its diminutive floor size. People are packed together in a way which wouldn’t be allowed in a new building because of modern fire regulations. This results in a very lively sound; the music reverberates and echoes for a long time, bouncing around the hall, creating sound that seems to envelope the listener. It’s ideally suited to the music of Brahms, Bruckner, and Mahler; these famous composers all had music premiered here.

360 video

Location and logistics

Website: Book a concert, or second best, go on a tour.

Credits

Photo: By Li Sun – Own work, CC BY-SA 3.0

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

Great Court British Museum

An amazing cacophony in the largest covered public square in Europe

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(5 Votes, average 4.20)
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This place has a remarkable acoustic which complements the beautiful architecture. Opened in 2000, the court wraps around the circular central reading room, providing a huge circulation space with cafes, information points and shops. The sound of people talking and walking echoes throughout the space. The soundscape is a cacophony of indistinct speech and other blurred sounds.

Large reverberant spaces are familiar to us all, but the sheer size of the Great Court along with the number of people creating the sound makes this space ear-conic. The only downside to the great sound effect is that it makes conversations difficult to hold in the cafes – as I found out when I foolishly tried to hold a business meeting there.

Incidentally, audio nerds can also wander around and look for the Intellivox loudspeakers; an interesting technology which attempts to make public address announcements intelligible in cavernous spaces.

Logistics

The British Museum, Great Russell Street, London, WC1B 3DG. Can only be visited when the museum is open. The Great Court is free to enter. Most impressive when busiest (weekends, school holidays etc.)

Credits

  1. http://www.britishmuseum.org/the_museum/history_and_the_building/great_court.aspx
  2. Photo: M.chohan
  3. Sound ERH (c) some rights reserved