Certain extended techniques, such as multiphonics, will only be effective at specified dynamics as shown in the multiphonics fingering chart. See Robert Dick, The Other Flute , for a complete listing of standard multiphonics and dynamic for the C flute. It should also be noted that different instruments respond in different ways to many extended techniques, and it is often advisable to check details such as this with the player concerned.
Multiphonics using partial key venting are generally less stable and have less projection than those using completely closed keys. As a general rule, multiphonics which have small intervals are softer than those with a wide intervallic range.