What would happen if two sonic booms merge?

Say, if two capable planes flew towards each other (but not so that they'll collide) at speeds higher than the speed of sound (thus producing a sonic boom) what would a person who may be standing at the point at which each plane crossed paths experience? Would the sonic boom be twice as loud? Would the sonic booms be cancelled out? Would a wormhole be created into the future? (Just kidding about the last question!)