s are classified into THREE , those are Ultrasonic SoundInfrasonic SoundAudible SoundULTRASONIC SOUNDUltrasonic sounds are those sounds which are higher than 20000 Hertz. Ultrasonic  sound have frequencies which are higher than the range of frequencies  not audible by human EARS.Some animals can hear this ultrasonic sounds .Some APPLICATIONS of UltrasoundUltrasonic sound have application in many fields , these includes :-SONARSONAR technique in which ultrasonic sound waves are USED to  detect objects under the surface of the water.Detection of cracksUltrasonic sound waves are used to detect cracks in dams , bridges and other buildings.Medical FieldUltrasonic sounds founds many application in medical Field ultrasonic sounds are used in scanning .INFRASONIC SOUNDUltrasonic sounds are those sounds which are lower than 20 Hertz. Ultrasonic  sound have frequencies which are lower than the range of frequencies  not audible by human ears.Elephants can use infrasonic waves to communicate with each other.Some Application of Infrasonic SoundInfrasonic Sound is used by some animals LIKE elephant for communication .Infrasonic sound is used for detecting earthquakes,volcanic eruption , etc.AUDIBLE SOUNDAudible sounds are those sound which are audible by human ears. Audible range of human ear is from 20 Hertz to 20000 Hertz .