Parts of the ear:

Ear lobe - concentrates high frequencies, gives sense of direction. Animals control ear lobes.

Ear canal - open-closed resonator, enhances frequencies around its fundamental resonance, which is in the range of 2000 – 5000 Hz. Resonant frequency used to determine length of canal for fitting hearing aids.

Ear drum - converts sounds waves to mechanical vibrations, much like a microphone.

Inner ear bones - transfers mechanical energy to oval window on cochlea. Protects against loud noises.

Cochlea - fluid filled canal with Basilar membrane running along its length. At the near end the membrane is narrow and stiff (high frequencies) and at the far end the membrane is wide and loose (low frequencies).

How is pitch or frequency determined?
Range of hearing: 20-20,000 Hz. Range in volume 10⁶!

Sound processing is very complex and involves positive feedback. Feedback enhances sensitivity, but can go above one and ear starts vibrating by itself. The ear actually produces a tone – this is the "ringing" in your ear.

1. Basilar membrane resonates when a sounds wave enters: Different parts resonate at different frequencies. Position on membrane corresponds to different frequencies.
2. Resonant frequencies are spaced logarithmically – like a piano. An interval is always the same distance. This is the only way to cover a larger range of frequencies. Compare to linear scale (100,200,300,400 etc.)



3. A single input frequency can activate a range of nerves on the Basilar membrane:

This is the response to a pure tone. There is the center – the position of the peak, and a width, called the Critical Bandwidth.