Pure-tone audiometry of a 30 year old field worker shows Carha's notch. He has the following condition:

The hallmark of bone conduction thresholds in otosclerosis/otospongiosis is the Carha notch. This is characterized by the elevation of bone conduction thresholds of approximately 5, 10, and 15 dB at 500, 1000, and 2000 Hz, respectively. The Carha notch is thought to result from the disruption of normal ossicular resonance, which is approximately 2000 Hz. It is therefore a mechanical phenomenon and not a true reflection of cochlear reserve since it reverses after successful surgery.