Anatomy of the Ear

Without our ears sound is pretty much meaningless. It is the anatomy of the ear that allows us to perceive the disturbances of air particles in our environment and then convert them into something meaningful. Our ears help us to survive in our environment. They add meaning to what we see. They allow us to enjoy music or a pleasant conversation.

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The anatomy of the ear, while sophisticated in design, is conceptually very simple. It can be broken down into 3 basic sections:

  • The Outer Ear
  • The Middle Ear
  • The Inner Ear

    Let's take a closer look at each:

    The Outer Ear

    The outer ear consists of the fleshy part of the ear that sticks out of the side of your head called the pinna and the ear canal. The primary purpose of the pinna is to collect sound and funnel it in to the ear canal.

    Sound waves that are coming directly toward us are going to be focused and funneled into the ear canal with the greatest efficiency and frequency response. When sounds come from above, below or behind, they still enter the ear canal but in a slightly different fashion. The sound has to wrap around the pinna and therefore is not focussed with the same efficiency.

    When sound wraps around the pinna, it creates subtle variations in the frequency response and the amplitude. These variations in the anatomy of the ear help us to perceive the direction from which a sound source is coming. This is a major component of the concept of localization which we will talk about in later lectures.

    The ear canal acts as an amplifier that focusses the sound and allows the tympanic membrane, or eardrum, to respond to the fluctuations in air pressure most efficiently. It also serves as a mechanism to protect the middle and inner ear.

    The Middle Ear

    The middle ear starts at the eardrum which is, fundamentally, the basis for the design of the diaphragm of a microphone. Attached to the inside of the eardrum are 3 bones. These 3 bones convert the acoustic air pressure changes into a mechanical signal. Together these 3 bones are called the ossicles.

    Attached to the eardrum is the malleus which is the hammer. The malleus is attached to the incus which represents the anvil. The anvil is attached to the stapes which is the stirrup. It is called the stirrup because it is U-shaped. These 3 bones help to protect the inner ear from the pressure changes coming from the outer ear.

    The stapes is connected to the oval window which is the gateway to the inner ear. There is a tube that connects the middle ear to the throat which helps to equalize the air pressure between the inner ear and outer ear. It is called the eustachian tube.

    If you are in a plane that is rising in altitude very rapidly, you will feel pressure in your ears that can be quite painful. The act of swallowing manipulates the eustachian tube which allows the air pressure in the middle ear to equalize. This is one of the reasons that it so dangerous for people who have severe head colds to travel in planes. If the area of the eustachian tube is clogged up you may not be able to equalize the pressure effectively. The resulting buildup of pressure can become quite painful.

    The Inner Ear

    The anatomy of the ear is most complex in design at the start of the inner ear. The inner ear starts with the cochlea. The cochlea is actually contained inside of a bone and is about the size of a pea. It is snail shaped and is filled with fluid that amounts to the volume of a single drop. When the oval window is excited by the action of the ossicles, the fluid inside the cochlea sloshes around in waves.

    Inside the snail shaped cochlea is the basilar membrane which is covered with hair cells. The movement of the fluid inside excites these hair cells. The hair cells, through the basilar membrane, excites the nervous system to which it is attached.

    The basilar membrane, through the nervous system, creates electrochemical signals that get sent to the brain. These electrochemical signals are interpreted by the brain as the sensation of sound.

    Moving On...

    The auditory system is an incredible mechanism and has served as a template for the design of many of the microphones and audio components we use today. The study of the anatomy of the ear and the way we perceive sound has forever shaped the way we approach recording. How could it not…

    Understanding the basics of the hearing mechanism and how it works is the gateway into the basic of audio. If you can understand the the anatomy of the ear, its limitations, its strengths and weaknesses, and how it affects our perception of sound, you will go a long way to understanding the audio basics principles that follow.

    It is very easy to take this information for granted, but this is the foundation for everyone's perception of hearing (your audience). The care and understanding of this mechanism is critically important to your success and your own health as an engineer or music producer. Listen to the audio below for more information. The next audio basic will discuss ways to best protect your hearing, it's about a lot more than just wearing earplugs…

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    Protecting Your Hearing

    Temporary Threshold Shift

    Critical Listening

    Audio Ear Training

    Physics of Sound

    The Decibel

    Fletcher and Munson

    Selective Hearing

    Speed of Sound and Wavelength

    Acoustical Phase

    The Sound Envelope

    Return to Audio Basics

    Return to Home From Anatomy of the Ear

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