Carhart's notch in audiogram is deepest at the frequency of:
(b) 2kHz or 2000Hz(Ref. Scott Brown, 8th ed., Vol 2 1070)In otosclerosis there is an increase in BC threshold of approx. 5dB, 10dB and 15dB at 500,1000,2000Hz respectively. So the deepest dip is at 2kHz which is known as Carhart's notch.At 4or8kHz, there is no hearing loss in otosclerosis.
0.5 kHz
2 kHz
4 kHz
8 kHz
Otosclerosis