<prompt> Carharts notch in audiogram is deepest at the frequency of:0.5 kHz2 kHz4 kHz8 kHz  <response>: b 2kHz or 2000HzRef. Scott Brown, 8th ed., Vol 2 1070In 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 Carharts notch.At 4or8kHz, there is no hearing loss in otosclerosis. 