For a deflagration the reaction front propagates at a speed less than the speed of sound.
The pressure front moves at the speed of sound in the unreacted gas and moves away from the
reaction front. One way to conceptualize the resulting pressure front is to consider the reaction
front as producing a series of individual pressure fronts. These pressure fronts move away from
the reaction front at the speed of sound and accumulate together in a main pressure front. The
main pressure front will continue to grow in size as additional energy and pressure fronts are
produced by the reaction front.