Sonic boom and the "rise time" of the shock which makes the boom seem louder. On most aircraft designs the characteristic distance is about , meaning that below this altitude the sonic boom will be "softer". However, the drag at this altitude or below makes supersonic travel particularly inefficient, which poses a serious problem. The pressure from sonic booms caused by aircraft often are a few pounds per square foot. A vehicle flying at greater altitude will generate lower pressures on the ground, because the shock wave reduces in intensity as it spreads out away from the vehicle, but the sonic booms
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