Under the Microscope: The sounds we hear can induce feelings that range from intense pleasure to severe discomfort - compare the sound of Beethoven's Emperor Concerto with the sound of scratching your nails across a blackboard.
However, we are also affected by sounds that we cannot consciously hear. Sounds that vibrate at a frequency below the threshold of human hearing are called infrasound. Although we cannot hear infrasound, it affects our bodies.
Studies indicate that exposure to infrasound can induce feelings of joy, anger, fear, apprehension, or an enhanced sense of the spiritual. Certain fearful, spine-tingling feelings commonly experienced in "haunted" locations have been explained away on the basis of exposure to infrasound. Also, the enhanced spiritual feelings aroused in many by religious organ music is at least partly explained by infrasound emanating from the longer organ pipes.
What we normally hear as sound is a vibration in the air, although sound can be transmitted through any material medium. The faster the vibration (the higher the frequency) the higher the pitch of the sound. Frequency is measured as cycles per second. A frequency of one cycle per second is called a hertz (Hz). One thousand Hz is a kilohertz (kHz). Most people can hear airborne sound that vibrates between 20 Hz and 20 kHz. Sound with a frequency below 20 Hz is too low to be detected by the human ear and is called infrasound. Infrasound can travel long distances and get around obstacles with little dissipation.
We are continually exposed to a background of infrasound from both natural and artificial sources. For example, thunder storms, earth tremors, ocean waves, and volcanic eruptions generate infrasound. Infrasound also emanates from factories, lorries, aircraft, turbines on wind farms, and many other human sources. It has been suggested that the enhanced infrasound background in built-up areas is a possible cause of city dwellers' stress.
Many animal species communicate with infrasound, e.g., rhinos, cod, squid, pigeon, elephants, whales and guinea fowl. Animals that communicate using infrasound instinctively migrate, home, or call one another over great distances. Infrasonic animal calls were discovered in the 1950s with the detection of the call of the north Atlantic fin whale - mistaken originally for a Soviet submarine.
Elephant infrasound was discovered in 1984 by Katie Payne. Infrasound solved several mysteries about elephant society, particularly the male's ability to quickly find females for breeding. The female elephant is in oestrous for only about four days in every four years. When she is ready to mate, she sends out a distinctive infrasonic call that attracts males up to 4 kilometres away.
In September 2002 a study was carried out into the effects of infrasound at Liverpool's metropolitan cathedral. Scientists analysed the responses of 250 people who listened to a concert of four pieces of piano music played by Russian pianist Evgenia Tchdinovich. Infrasound vibrations were also broadcast to the audience at certain times during the concert. The guests at the concert were asked to fill in questionnaires compiled by psychologists about how they felt at different moments.
The results showed that people's pre-existing emotions intensified when the infrasound was broadcast. People who felt uncomfortable when the concert began found their mood turned into anger when the infrasound commenced. Others who had been happy when the concert commenced became quite joyful during the infrasound. Some physical effects also correlated with the infrasound, including tingling in the back of the neck and strange feelings in the stomach. In general people found that they experienced more in-depth versions of the emotions they were feeling before the infrasound began.
Infrasound has emanated from organs in churches for at least 250 years and has helped to create grand, spiritually moving music. There is a high probability that some pipes in any large cathedral organ are 32 feet (9.75 metres) long. These pipes produce infrasound. The organ in St Alban's Abbey, Hertfordshire emits sound at 14 Hz.
Because low frequency sound can cause people to have unusual experiences, it has been suggested that infrasound may be present at some "haunted" sites, causing people to have odd sensations attributed to ghosts. It has been reported that infrasound can induce cold shivers, feelings of discomfort and apparitions in peripheral vision.
On a more ominous note, there are stories of the use of sound by the military as a weapon.
In the 1950s French acoustic engineer Vladimir Gavreau experimented with infrasonic weapons. He is said to have constructed a giant six-foot whistle, powered by compressed air, which reportedly fatally resonated and scrambled the internal organs of its operator. Gavreau ceased his experiments and his plans were reportedly seized by the French authorities who declared that he had not been working on a weapons system.
However, this was at the height of the Cold War and many countries were secretly spending large amounts of money to develop new weapons. William Reville is associate professor of biochemistry and director of microscopy at UCC