What are Quattrosonics sonic soot blowers?

Sonic soot blowers are pneumatically operated horns that produce 'low frequency – high energy' sound waves, which de-bond particulate in a 360° radius, travel at a speed of around 344m (1128 ft) per second through air and at up to an amazing 5000m (16,400 ft) per second through solids. Compare this to a bullet fired from a gun which travels at a speed of around 1,500 miles per hour which equated to 670m (2,200 ft) per second.

What is sound?

Sound may be described as the passage of pressure fluctuations through a medium by means of a vibrating source.

Why different frequencies?

The higher the frequency, the shorter the wavelength path = high intensity localised power [1-2 metres]; the lower the frequency - the longer the wavelength path = powerful long distance deep penetrating
power [20 - 25 metres]

The ear does not really 'hear' sound, rather it is a pressure sensitive mechanism and detects these rapid pressure fluctuations which it interprets as sound.