<prompt> Carharts notch in audiometery is seen in -Ossicular discontinuityHaemotympanumOtomycosisOtosclerosis  <response>: Carharts notchBone conduction is normal in otosclerosis.In some cases there is a dip in bone conduction curve which is maximum at 2000 Hz 2 KHZ called as Carharts notch.Carharts notch is seen only in bone conduction curve.It disappears after successful stapedectomystapedotomy.The reason why it disappears after successful surgery is that when the skull is vibrated by boneconduction sound, the sound is detected by the cochlea via 3 routes: Route ais by direct vibration within the skull. Route bis by vibration of the ossicular chain which is suspended within the skull. Route cis by vibrations emanating into the external auditory canal as sound and being heard by the normal air-conduction route.In a conduction type of hearing loss as in otosclerosis the latter two routes are deficient but regained by successful reconstruction surgery. Hence bone conduction thresholds improve following surgery.ALSO KNOWDip in noise induced hearing loss is seen at 4 KHZ.In noise induced hearing lossDip is seen in both air and bone conduction curves.Trough shaped audiogram is seen in congenital SNHL.Flat audiogram with moderate to severes SNHL is characteristic of presbycusis. 