I didn't understand the explanation- how does the length of basilar membrane inc from basal to apical coil?

I didn’t understand the explanation- how does the length of basilar membrane inc from basal to apical coil?

The thickness , mass and height of the organ of corti increases from the base to the apex. The difference in the ability of the different parts of organ of corti to sense different frequencies is because of the changes in its inherent mechanical properties.

It’s like how the different strings of the guitar which produce different frequencies of sound have different thickness and length ( tension )