“Sound is a form of energy which exists as variations of pressure in a medium such as air and travels as longitudinal harmonic waves.” This was taught to me in the 7th grade by an old physics teacher who used to wear a soda bottle glass and talk in a small husky voice.
Sound is an existence right from the Big Bang. It basically, is the sensation produced by stimulation of the organs of hearing but widely, is a physical phenomenon that may or may not be apparent to the senses. If a tree falls in a forest and no-one hears it, does it make any sound? This was a mystery which puzzled our philosophers for thousands of years. But, now we know that unheard sound exists and has various applications.
Difference between sound and audio.
Many people have asked me what the difference between sound and audio is. Audible sound is what is generally known as audio. I know it is needless for me to say, human hearing range is limited within 20 and 20000 Hz, but that doesn’t mean that Sound is limited to that range. Sounds below 20 Hz are infrasonic and above 20000Hz are ultrasonic sounds.
Infrasounds cannot be heard by the human ear. Examples are, sounds from earthquakes, lightning’s, explosions, etc. An interesting fact is that Whales, Elephant, Rhinos and alligators use infrasound to communicate with their fellow beings. Infrasonic sounds have even got the capability of affecting the human moods negatively. The ‘17 Hz tone experiment’ done by a team of researchers from UK had found that the presence of a 17 Hz tone for half an hour made them anxious, uneasy and extremely sorrow. Some of the applications of infrasound’s are Ballistocardiography, Seismocardiography, monitoring earthquakes, etc.
Ultrasounds, sounds above 20000Hz are emitted by a lot of animals such as Bats, Dogs, Fishes, Horses, etc for communication. It has got a lot of medical applications including Sonography, HIFU surgeries, Ultrasound scan, etc. Ultrasounds are also used by the army in the Real time locating systems and by the navy in SONAR: ‘SOund Navigation and Ranging’.
Sound is acoustically measured using the unit ‘Decibel’. One decibel is the smallest change in volume a human ear can perceive. A small whisper would be around 15 dB, whereas a rock concert would be 120 dB.
Artistic Sound
Can you imagine entertainment without sounds? What is music and cinema if there is no sound? How would it be if a football stadium is totally silent while a match is on?
Every sound that is formed as a consequence of an idea is artistic sound. They influence our intellect and affect our emotions. Sounds are language for communication.
Music is the main form of artistic sound. Music is technically structured in various different ways all across the world or it is classified as several genres. Any music, be it structured or not, if able to control natural behavior or mood, then it is purely artistic.
Another main form of artistic sound is Sound art. Sound art is a form of contemporary art performed on an interdisciplinary field where the ideas are inceptions of the sound artist.
Sound plays a major role in some displayed art forms like theatre, films, etc. It helps to enhance the mood of a scene. It is the soundtrack in the film ‘Apocalypse Now 
Read about more on scientific and artistic sound in here at ‘Touch Your Sound’.
References:
17 Hz tone experiment : http://news.bbc.co.uk/1/hi/sci/tech/3087674.stm
