Why do relatively small but high-frequency pressure changes cause hearing loss, but large but slow pressure changes don't?

Question

Air at sea level has a pressure of ~101kPa, while at 1000m elevation it's ~89kPa, so there's a difference of ~12kPa between these two elevations.

A sound level of 140 dB is so high, that it can cause immediate injury to the hearing system, even though it's just ~200Pa.

How come, that a sound pressure of 200Pa can permanently damage your hearing even with short exposure, but a hike up a small mountain where you have a pressure difference that's almost two orders of magnitude higher is not dangerous at all?

Answer 1

1. The ear has a "high-pass" filter removing very low frequencys. If you go very fast up or down the eardrum may rupture, but it will heal. If you go slower pressure is equalized through the Eustachian tube.

2. Hearing loss from high sound levels is because hair cells in the cochlea are "filtered" to receive certain frequencys in different places. A high frequency of sufficient volume may damage or kill a sections of hair cells but hardly influence other hair cells. And as we have no hair cells for very low frequencys, there are none to be damaged.

Answer 2

There's a couple things to consider. Like the previous answer, damage to the small hairs (recruitment is the term for the condition) can happen

The tympanic membrane is a muscle as well, which can be damaged if acted upon by intense pressure levels. As an example, if you put a speaker next to a wall, and set it to -64dB, you won't hear anything on the other side. If you crank it to 120dB, you will. Your tympanic membrane is the wall, and if it can block spl, it will, but it can't block everything after a certain point.

The less attenuation from the tympanic membrane, the more damage to other parts of the ear.