Sonic boom is sufficiently long. A new metric has emerged, known as "perceived" loudness, measured in PLdB. This takes into account the frequency content, rise time, etc. A well-known example is the snapping of one's fingers in which the "perceived" sound is nothing more than an annoyance. The energy range of sonic boom is concentrated in the 0.1–100 hertz frequency range that is considerably below that of subsonic aircraft, gunfire and most industrial noise. Duration of sonic boom is brief; less than a second, 100 milliseconds (0.1 second) for most fighter-sized aircraft and 500 milliseconds for the space shuttle or Concorde jetliner.
Speed of sound Speed of sound The speed of sound is the distance travelled per unit time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about 343 meters per second (1,234.8 km/h; 1,125 ft/s; 767 mph; 667 kn), or a kilometre in or a mile in . It depends strongly on temperature, but also varies by several meters per second due to which gases are present. The speed of sound in an ideal gas depends only on its temperature and composition. The speed has a weak dependence on frequency and pressure