Sound is a physical phenomenon that stimulates the sense of hearing. It is detected by humans whenever vibrations of frequencies ranging from about 20 hertz to 20 kilohertz being propagated through air can reach the inner structure of the ear. Frequency of vibrations that cause the phenomenon of sound is measured in hertz, where one hertz denotes one cycle of vibration in a second. Sound waves travel at a speed of nearly 1,200 kmph (740 mph). The speed varies under water and at higher altitudes. Sound energy is required to be studied to achieve good acoustics.
- For more information, see the article about Sound.