Vignette

A 34-year-old reports hearing that has slowly worsened over several years, worse in one ear, with no pain or discharge. They mention hearing better in noisy places. Otoscopy is normal.

O Right ear, air
X Left ear, air
< Right ear, bone
> Left ear, bone

Signature: Low-frequency conductive loss with an air–bone gap; bone conduction shows the Carhart notch dipping at 2 kHz.

Figure 1. The audiogram. Bone conduction shows a dip at 2 kHz. Tympanometry is normal.

Question

The bone-conduction dip at 2 kHz is best explained by which of the following?

References

[14] Carhart R (1950). Clinical application of bone conduction audiometry.