"Sound pressure levels above 194 dB at sea level produce waveforms that are distorted. Sound waves are made up of rarefaction and compression cycles but when the compression half of the wave cycle is double normal atmospheric pressure and the rarefaction half of the cycle reaches perfect vacuum (no further air molecules to remove) then the only possible increase in sound level can be achieved on the compression side of the waveform. The rarefaction half of the cycle will be clipped at any level above 194 dB. Examples of such an occurence are large-scale manned rocket launches, sonic booms, munitions explosions, thunder, earthquakes and volcanic explosions.[6]"
Updated! "As sound pressure levels approach 191 dB in air at sea level, their waveforms become distorted; the exact level at which this happens varies with the barometric pressure. Sound waves are made up of rarefaction and compression cycles, but when the compression half of the wave cycle is double atmospheric pressure, the rarefaction half of the cycle approaches a perfect vacuum (no further air molecules to remove). At this point, the only possible increase in sound level that could be achieved is on the compression side of the waveform. (The rarefaction half of a sine wave would be clipped at any level above about 191 dB.) Any wave approaching these intensities is no longer considered sound, but a shock wave. Examples of such an occurrence are large-scale manned rocket launches, sonic booms, munitions explosions, thunder, earthquakes and volcanic explosions."
