The bigger and heavier the aircraft, the more air it displaces. The shock wave forms a cone of pressurized air molecules which move outward and rearward in all directions and extend to the ground. As the cone spreads across the landscape along the flight path, they create a continuous sonic boom along the full width of the cone's base. The sharp release of pressure, after the buildup by the shock wave, is heard as the sonic boom. It is the rate of change, the sudden onset of the pressure change, that makes the sonic boom audible.
All aircraft generate two cones, at the nose and at the tail.
They are usually of similar strength and the time interval between the two as they reach the ground is primarily dependent on the size of the aircraft and its altitude. Most people on the ground cannot distinguish between the two and they are usually heard as a single sonic boom. Sonic booms created by vehicles the size and mass as the space shuttles are very distinguishable and two distinct booms are easily heard. A larger and heavier aircraft must displace more air and create more lift to sustain flight, compared with small, light aircraft. Therefore, they will create sonic booms stronger and louder than those of smaller, lighter aircraft.