Threshold for bone conduction is normal and that for air conduction is increased in disease of:
Middle ear
Inner ear
Cochlear nerve
Temporal lobe
Threshold for air conduction is increased (i.e. low frequency sounds are not heard well) whereas that of bone conduction in normal i.e. Bone conduction > air conduction which is seen in conductive deafness. Conductive deafness occurs in lesions of either external ear, tympanic membrane, middle ear or ossicles up to stapedio-vestibular joint.