Outer Ear Physiology

Acts as a collecting horn that gathers sound and funnels it down the ear canal

pinna

The level of the signal to reach the eardrum depends on:

Properties of the signal, resonance effects of the outer ear structure, head and torso effects, environmental factors

Wavelength

the distance covered by one cycle of a propagating wave

Amplitude

Magnitude of the air particle’s displacement

Starting phase

The relative position of the object at the instant in time it begins to vibrate

Period

Time it takes to complete one cycle

Frequency

How many cycles are completed per second, measured in Hz (cycles/sec)

Frequency and wavelength are:

inversely related

Amount of gain given by concha

10 dB gain @ 5k Hz

Amount of gain of EAM

10-15 dB gain between 3 and 4k Hz

Resonant frequency of EAM

~3500 Hz

0 azimuth is where

directly in front

90 azimuth is where

to the right

180 azimuth is where

behind

Interaural level difference

Difference in sound level between left and right ear

ITD should be largest at which degree azimuth

90

Interaural time difference

Difference in time it takes stimulus to reach each ear

Head shadow effect related to shooting a gun

The sound will be more impactful in opposite ear. Right handed shooters should expect more hearing loss in the left ear due to the right ear being guarded

Head Related Transfer Function (HRTF)

How sound is filtered by the body as it travels to the eardrum

How does the outer ear provide protection for the inner ear?

Bony cartilage junction, osseous portion, and TM