Which frequency sounds are typically harder to hear due to problems stiffening the ear system?

The correct choice is high frequencies. Stiffness in the ear system generally affects the ability to perceive higher frequency sounds due to the mechanics of the cochlea and middle ear. When the structures in the ear become stiffer, often due to age or other conditions, the ability to process and transmit these higher frequency vibrations is diminished.

This is because high-frequency sounds require a different response from the hair cells in the cochlea, which are less efficient at responding to stiffer conditions. In contrast, low-frequency sounds typically require more movement of the structures involved in hearing and can still be perceived even if the ear system has increased stiffness. This effect explains why individuals with stiffer ear systems often report difficulty hearing high-pitched sounds, such as consonants in speech or certain musical notes, while they may still hear lower-pitched sounds clearer. Thus, high frequencies are significantly more affected by increased stiffness in the ear system.