For human beings, sound is a perception of waves in the brain. However, physically it is the propagation of vibration as an audible pressure wave which requires a medium for its transmission. The medium need not be air always as loud sounds can also propagate through water.
A group of scientists of SLAC National Accelerator Laboratory, Department of Energy took an X-Ray laser to generate a very loud sound in water. The team reported that the loudness was such that it was almost at the edge of being the loudest sound which could be produced through water. The results of the experiment were reported in Physical Review Fluids.
Physicist Claudiu Stan of Rutgers University Newark said that the produced sound was slightly below the threshold that would be enough for boiling the water. To achieve this result, scientists used an equipment known as Linac Coherent Light Source (LCLS). This is a very powerful X-ray laser which is capable of creating molecular black holes and also raise the temperature of water to 100,000 degrees celsius in a time period which is lesser than millionth of a millionth of second. The X-rays produced by the laser have very high brightness and is considered to be the most powerful X-ray source in the world.
LCLS was used by scientists to understand how the high-intensity sound waves that generate very loud sounds impact materials. For the experiment, researchers blasted very small liquid water microjets with a thickness less than hair strand in a vacuum chamber having X-ray pulses.
As the water stream was intercepted by the laser, very rapid ionisation occurred in the microjet due to heating of the water leading to its vapourisation which in turn produced shock waves.
The researchers found out that these shock waves had peak pressures which match with high sound intensity and sound pressures above 270 decibels. This is louder than a rocket launch or a jet plane taking off. It has been found that it is not possible to reach an intensity louder than this as it would result in the break down of water.
Researchers explained that the magnitudes of the sound intensity were restricted since the wave would destroy the medium of propagation though cavitation. This makes the ultrasonic waves in jets as one of the most intense sounds possible to be generated in water. Scientists also estimate these sound waves to be the highest intensity sound waves produced in water till date.