Mechanical waves with slower speed than sound Sound is mechanical waves of high and low air pressure transmitting with 300m/s. Are there high and low air pressure waves transmitting with lower speeds? How are they produced?
 A: The speed of mechanical sound waves through the air at 0 degrees C is 331 m/sec.  But sound can travel at many different speeds, depending on the medium it propagates through and the temperature and pressure, among other variables.
What we call sound is any mechanical wave within the range of human perception that is transmitted to our eardrums via the air.  Here is a table of speeds of sound waves through several different materials: http://hyperphysics.phy-astr.gsu.edu/hbase/tables/soundv.html.  You'll notice that in liquids and solids, the speed is faster than in air.  Generally, a lattice of molecules transmits mechanical waves faster than gas because they impact each other more quickly than a loose configuration.
Generally, the speed of sound in any medium may be modeled as:
Velocity = √ (elastic property / inertial property)
Elasticity is the tendency of a material to snap back to its original shape after deformation.  Inertia is the difficulty of moving a material.  As temperature rises, velocity of sound waves will also rise, as the air molecules become more energetic.  If the air is humid, sound travels faster because water vapor has a lower molecular mass than dry air, and therefore the average molecule has less inertia to overcome.  Here is a calculator which allows you to compute the speed of sound in air under various temperatures: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe3.html#c1
As you can see from the calculator, you can significantly reduce the speed of sound by lowering the temperature of the air.
