The UK's five weirdest sounding places
We're all familiar with sightseeing, but what about "soundseeing"? There are places where what you hear is not what you would usually expect, says Trevor Cox, professor of acoustic engineering at the University of Salford.
From beeping horns and workmen drilling roads, through to birds and wind whistling through the trees, we are never in silence - even in the remotest parts of the UK.
But in some places what you hear is different to the usual cacophony of sound that people's ears are used to. So where are the strangest sounding places in the UK and what makes the noises so different?
St Paul's Cathedral Whispering Gallery, London
The Whispering Gallery at St Paul's Cathedral in London is one of the few tourist sites known for its acoustics.
Thanks to a quirk in the building, designed by Sir Christopher Wren, a whisper can travel around a wall.
Stand on one side of the dome, with a friend 110ft (33m) away on the other, and whisper into the wall. The sound will skim around, hugging the wall, and be clearly heard by your friend.
Nobel-prize winning physicist CV Raman described what he called "mocking whispers" in the gallery.
"In response to ordinary conversation, strange weird sounds and mocking whispers emanate from the wall around. Loud laughter is answered by a score of friends safely ensconced behind the plaster."
The gallery in St Paul's is particularly adept at transporting whispers.
The sound is trapped against the inside of the curved dome wall, which is why it sounds surprisingly loud at the other side and appears to emerge from the wall.
This strange feature has been attributed to the slight curve of the walls. By tilting the walls inwards at the top, less sound goes upwards and gets lost to the top of the dome.
But like most whispering galleries, this magical property is an accidental by-product of the architectural design.
Wormit water reservoir, Dundee
The old water reservoir in Wormit near Dundee lies disused and hidden from view under someone's back garden.
It was built in 1923 in anticipation of the population of Wormit growing, but war intervened and the town never grew to be very big. Eventually, the cost of maintaining the oversized reservoir led to it being decommissioned.
It has few visual charms, it is just a vast concrete box about 200ft (60m) long, 100ft (30m) wide and 16ft (5m) high. It has a forest of concrete pillars regularly spaced about 23ft (7m) apart and holding up the concrete ceiling.
But as you talk the acoustic immediately reveals itself. A rumble builds up and hangs around like a smog. There are balloon popping sounds like a gun being fired, with a boom that reverberates around for ages.
The time it takes sound to die away is an important measure of room acoustic quality. In a classroom it is relatively short, so a teacher's words do not overlap and make speech unintelligible. Concert halls for an orchestra are designed with a longer sound decay, because the reverberation plays an important role in enhancing the music.
The sound takes ages to die away in Wormit. In most rooms the sound dies away because every time it reflects from a wall a little bit of energy is lost. In Wormit the room is very large so the time between reflections is very long.
Also the concrete walls are almost impervious to sound and so not much energy is lost each time the sound bounces off the walls. This is why it takes some time to die away. It is like a huge cathedral, with the great advantage that you do not have to wait for an evangelical service to whoop and clap.
Greenwich foot tunnel in London
This foot tunnel under the Thames might not be much to look at, but when the sound artist Peter Cusack asked people about their favourite sounds of London it was a popular answer because of the way it distorts voices.
Sound waves bounce back and forth across the width of the 1,215ft (370m) tunnel, distorting voices using the same physics which make some people think they can sing well in a shower stall.
You can also really let rip and hear the sound go up and down the length of the tunnel.
The recording of a skateboarder passing the microphone - listen to the audio clip on the right - sounds like a freight train because of the reflections from the tunnel walls.
When the skateboard crashed to the floor there was a reverberating echo as it hit the floor. The hard tiled walls mean the crash rattles around the tunnel for ages before dying away.
With nowhere else for the sound to go, the echo is impressively loud, travelling hundreds of metres to the end wall before returning.
Bitterns at Ham Wall, near Glastonbury
Ham Wall wetland reserve near Glastonbury in south-west England is home to arguably the weirdest sounding bird in the UK.
Bitterns are reclusive wading birds, a type of heron which makes the most extraordinary bass sounds that can carry for many kilometres over the reed beds they live in.
Their call is often likened to a distant fog horn. It's no surprise as it is immensely powerful. At 101 decibels at 1m, it has a similar volume to a trumpet. And at about 155 hertz, a typical frequency produced by a tuba.
The booms sound like someone blowing across a large beer bottle in the pub. Exactly what the bittern is doing to make the sound is unknown, because it is a rare, secretive and well camouflaged animal.
Rare video footage has shown the bittern's throat swelling up and the body convulsing as the air is gulped in.
As the males call before mating, it is assumed the females use the loudness of the boom to assess the fitness of the competing males.
The strange sound could also be a form of defence, with the males also booming during nesting, suggesting it is also used to guard feeding territories.
Anechoic chambers around the UK
There is an anechoic chamber at the University of Salford and it is the closest you can get to hearing absolute silence.
It is so quiet, in fact, that you can hear the sounds your body makes, like the blood circulating in your head or a high-pitched hiss, which is thought to be caused by spontaneous activity in the auditory nerve fibres within your brain.
The rooms are used for carrying out acoustic tests such as measuring the performance of ear plugs, loudspeakers and microphones.
They are made so quiet by having multiple walls to stop noise getting in from outside. Like a modern concert hall, the Salford chamber is mounted on springs to prevent vibration entering the inner sanctum.
If you talk in the room your voice sounds odd, and very muffled, like listening in an aircraft when your ears need to pop. The walls, floor and ceiling are covered in vast wedges of grey foam which absorb the sound reflections you would otherwise hear from the chamber's surfaces.
This is a room that can be seen but not heard. Add the claustrophobic drama of being enclosed behind three heavy doors and this can get too much for some people who feel uneasy and ask to leave.