CONCEPT OF POWER
Research had shown that power may not change with the specs, but rather with the stringbed stiffness only because of trajectory of shots.
Softer or Firmer Stringbed?
People in the industry have been saying string looser for more power and tighter for more control. Both were right and wrong. If we define power as the speed of the ball / shuttlecock as it leaves the racquet, they are wrong. If they are referring to how far the shots will land in the court, they were right. If it is to be referred as tension only, then they would be totally off the tracks as the other 6 variables also do play their part in stringbed stiffness.
Speed and Trajectory
Lab tests that have been performed shows that a racquet and the speed at which it is swung do have a big effect on the speed of a ball / shuttlecock but the strings have none. The speed of a ball / shuttlecock as it leaves the racquet is not affected by stringbed stiffness, gauge of string, material of string or construction. A ball / shuttlecock will leave the strings at the same speed regardless of the specs of the string.
Though speed is NOT affected by the stringbed stiffness, but the trajectory of the ball / shuttlecock leaving the stringbed is greatly affected. All other things being equal, a ball / shuttlecock struck with a racquet with a softer stringbed will leave the racquet at a higher trajectory than a ball / shuttlecock struck with a racquet with a firmer stringbed. The higher trajectory ball / shuttlecock will travel farther landing deeper in the court.