Various physical objects which are in strong, liquid or gaseous state can sound. For example, the vibrating string or the current of air blown from a pipe.
The sound is the wave fluctuations of the environment perceived by a human ear. Sources of sounds are various physical bodies. Vibration of a source excites fluctuations in the environment which extend in space. Sound waves occupy frequency range from 20 Hz to 20 kHz, between an infrasound and ultrasound.
Mechanical oscillations arise only where there is an elastic medium therefore in a vacuum the sound cannot extend. Acoustic speed is a speed of passing of a sound wave on matter surrounding a sound source.
Through the gaseous environment, and in solid bodies the sound passes liquids with a different speed. In water the sound extends quicker, than in air. In solid bodies the acoustic speed is higher, than in liquids. For each substance the speed of distribution of a sound is constant. I.e. acoustic speed depends on density and elasticity of the environment, but not on the frequency of a sound wave and its amplitude. The sound wave can bend around the met obstacle. This phenomenon is called diffraction. At low sounds the diffraction is better, than at high. Here characteristic of a sound influences the direction of the movement of a wave, but not speed. A formula for calculation of acoustic speed in any single-component environment: with =1/√ρβ, where with — acoustic speed, ρ — environment density, β — adiabatic compressibility of the environment. For Wednesday from mix of liquids or gases the formula becomes complicated. In practice use the help tables containing already calculated values of acoustic speed in various substances. The condition of the environment through which there passes the sound wave depends on numerous external factors: temperatures, pressure, heat exchange between various objects. Therefore the help tables containing data on acoustic speed in various environments are surely annotated about the size of external parameters. Acoustic speed in air about 340 m/s, in water of 1500 m/s, in steel — near 5000m/page.