In which part of the ear does pressure need to be equalized when changing altitude or scuba diving?

Answer 1

The part of the ear that needs to be equalized during diving is called the Middle ear.

The pressure in the outer ear will change with the pressure in the water you are diving through. Between the outer ear and the middle ear is the Tympanic Membrane, or "Eardrum", which will bend, when pressure in the outer ear and the middle ear isn't equal, causing umpleasantness or pain.

This is countered by blowing air into the middle ear by what's called the Eustachian Tubes. By blowing extra air into the middle ear, the pressure inside the middle ear will increase, and since the Eardrum is the only flexible part of the middle ear, the increased pressure inside the middle ear, will cause the Eardrum to bend back to its original position. Hence, equalization...