Always been curious…
In: 3
I assume you mean the outer part of the ear, or the “pinna?”
Short answer: to amplify and direct sound towards the inner ear, and to process incoming sound frequencies so they’ll be understandable/react to the inner ear structure.
The folds both collect and direct sound into the ear, and also “add” directional information – where the sound is coming from – through a process called “frequency dependent amplitude modulation,” the nitty-gritty of which is a little too advanced for ELI5.
The folds also amplify the sound (by as much as 10 to 15 decibels), and filter it out – with the filtering preference set to the human speech frequency range.
In short, those folds do a lot.
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