There are 6 main modes of vibration that occurs in a guitar. (More on Modes Of Vibration) The Monopole mode of vibration is believed to be the most important mode of vibration, creating the majority of the sound. When this mode is active, the top(& back) is moving in a up and down motion.

The Monopole mobility is a measurement of how much the top moves under the forces of the string. If the top of the guitar is too heavy or over built, It will take more energy to move it.

"More Movement = More Sound"

Measuring the Mobility of a guitar involes measuring the deflection of the top under a known weight. Using this information we can calculate how much energy it takes to move the guitar top (s/Kg x10-3).

A guitar with a higher Monopole Mobility are more sensitive/responsive and this equates to more volume. 

All Murphy Guitars would measure high on Monopole Mobility and what you would hear when testing, is a guitar that is noticeably louder than the average.

On the left a graph showing the  Monopole mobility of a Murphy Guitar and others that have been tested.