why in different subs the speed of sound differs?

Sound is a type of longitudinal, mechanical wave. They need a medium to propagate and will not travel through a vacuum. Sound travels at different speed in different media. The speed of sound is determined by the density and compressibility (K) of the medium.

Density is the amount of material in a given volume, and compressibility is a measure of how much a substance could be compacted for a given pressure.

The denser and the more compressible, the slower the sound waves would travel. Water is much more dense than air, but since it is nearly incompressible the speed of sound is about four times faster in water than in air.

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