CTho9305 had the right idea but jospII was closer.
The first
Sonic boom is actually around the center of volume, not the leading edge. The location depends alot on the shape of the object. Sonic booms do not always travel in pairs.
Straight from
NASA: "
Sonic boom are created by air which reacts like a fluid to an aircraft as it nears the speed of sound. Air molecules are pushed aside and form a shock wave much like a boat creates a bow wave. The shock wave forms a cone of pressurized air molecules which move outward and downward to spread across the landscape along the flight path. The sharp increase of pressure is heard as the sonic boom.
Sonic boom intensity is governed by several factors such as weight, size, and speed of the aircraft, plus altitude, vehicle attitude and flight path, and weather or atmospheric conditions.
There are two types of
Sonic boom: N-waves and U-waves. The N-wave is generated from steady flight conditions, and its pressure wave is shaped like the letter "N." N-waves have a front shock to a positive peak overpressure which is followed by a linear decrease in the pressure until the rear shock returns to ambient pressure. The U-wave, or focused boom, is generated from maneuvering flights, and its pressure wave is shaped like the letter "U." U-waves have positive shocks at the front and rear of the boom in which the peak overpressures are increased compared to the N-wave.
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 (.100 seconds) for most fighter-sized aircraft and 500 milliseconds for the space shuttle or Concorde jetliner .
The intensity and width of a
Sonic boom path depends on the physical characteristics of the aircraft and how it is operated. In general, the greater an aircraft's altitude, the lower the overpressure on the ground. Greater altitude also increases the boom's lateral spread, exposing a wider area to the boom. Overpressures in the sonic boom impact area, however, will not be uniform. Boom intensity is greatest directly under the flight path, progressively weakening with greater horizontal distance away from the aircraft flight track.
Ground width of the boom exposure area is approximately one mile for each 1,000 feet of altitude; that is, an aircraft flying supersonic at 30,000 feet will create a lateral boom spread of about 30 miles. For steady supersonic flight, the boom is described as a carpet boom since it moves with the aircraft as it maintains supersonic speed and altitude.
Some maneuvers, diving, acceleration or turning, can cause focusing of the boom. Other maneuvers, such as deceleration and climbing, can reduce the strength of the shock. In some instances weather conditions can distort sonic booms."