<prompt> Frequency of Carharts notch is -1000 Hz2000 Hz3000 Hz4000 Hz  <response>: Ans. is b i.e., 2000 Hzo Dip in bone conduction in otosclerosis Carharts notch- 2000 Hzo Dip in noise induced hearing loss Acoustic dip- 4000 Hzo 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 Caharts notch,o 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,o So, Caharfs notch of otosclerosis is a dip for bone conduction, while acoustic dip of NIHL is for both air as well as bone conduction. 