Frequency of Carha's notch is ?

Ans. is 'b' i.e., 2000 Hz Dip in bone conduction in otosclerosis (Carha's notch) - 2000 Hz Dip in noise induced hearing loss (Acoustic dip) - 4000 Hz In otosclerosis bone conduction is usually normal (as would be in cases of conductive hearing loss). However, some cases show a dip in bone conduction on audiogram which is maximum at 2000 Hz (Caha's notch). In NIHL both bone conduction and air conduction are defective (as would be in SNHL) and there is a typical notch (acoustic dip) at 4000 Hz, both for air and bone conduction. So, Caha's notch of otosclerosis is a dip for bone conduction, while acoustic dip of NIHL is for both air as well as bone conduction.