The Collaborative International Dictionary of English v.0.48:

Loudness \Loud"ness\, n.
   The quality or state of being loud.
   [1913 Webster]

WordNet (r) 3.0 (2006):

loudness
    n 1: the magnitude of sound (usually in a specified direction);
         "the kids played their music at full volume" [syn:
         volume, loudness, intensity] [ant: softness]
    2: tasteless showiness [syn: flashiness, garishness,
       gaudiness, loudness, brashness, meretriciousness,
       tawdriness, glitz]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "loudness":
   amplitude, arsenic green, auditory effect, auditory phenomenon,
   blatancy, brazenness, clashing colors, coarseness, color clash,
   colorfulness, crassness, crudeness, crudity, dash, dazzle,
   dazzlingness, earthiness, extravagance, extravaganza,
   extravagation, flagrancy, flamboyance, flashiness, gaiety,
   garishness, gaudery, gaudiness, glare, glitter, gorgeousness,
   grossness, jaundiced yellow, jauntiness, jazziness, luridness,
   meretriciousness, noise, obscenity, obtrusiveness, panache, phone,
   rawness, ribaldry, roughness, rudeness, screaming color,
   sensationalism, shamelessness, shocking pink, showiness, sonance,
   sound, sound intensity level, sound propagation, sound wave,
   speech sound, sportiness, tawdriness, ultrasound, vulgarness