inaudibleness

from WordNet (r) 3.0 (2006)

inaudibleness
    n 1: the quality of not being perceptible by the ear [syn:
         {inaudibility}, {inaudibleness}] [ant: {audibility},
         {audibleness}]

from The Collaborative International Dictionary of English v.0.48

Inaudible \In*au"di*ble\, a. [L. inaudibilis; pref. in- not +
   audire to hear: cf. F. unaudible. See {In-} not, and
   {Audible}.]
   Not audible; incapable of being heard; silent. --
   {In*au"di*ble*ness}, n. -- {In*au"di*bly}, adv.
   [1913 Webster]