Threshold for bone conduction is normal and that for air conduction is increased in disease of -
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.
Ref. Dhingra 5/e, p 26
Middle ear
Inner ear
Cochlear nerve
Temporal lobe