The way our ear works relies on its structure. The ear has three main parts: the outer, middle, and inner ear. Each part has a specific job in capturing sound vibrations and converting them into a signal that travels through nerves to the brain. The ear's shape and functions have developed over time through evolution. This incredible organ has been essential to our survival. Understanding the physics of the ear is fascinating and helps us appreciate the complexity of the human body.

The ear system

The ear is made up of three distinct parts: the outer ear, the middle ear, and the inner ear. The outer ear is the part we can see, while the middle ear is responsible for focusing and transforming vibrations. The inner ear connects to our nerves and brain, making it an essential part of our body's communication system. These parts are defined by their position and functions. By understanding the different roles each part of the ear plays, we can appreciate the incredible complexity of this vital organ.

The outer ear

The outer ear is the part of the ear we can see. It's made up of the pinna and the ear canal, which ends where the middle ear begins at the outer part of the tympanic membrane. The pinna is shaped to catch sound waves from the front and has ridges to direct them towards the tympanic membrane. This structure helped our ancestors focus on sounds emitted by prey.

The middle ear is where sound waves are transformed from pressure waves to electrical signals. Three tiny bones in this section, called the malleus, incus, and stapes, act as mechanical transmitters of sound. This is an essential function because it acts as an impedance adapter, allowing us to perceive a wide range of sound amplitudes. The lower limit of perception is 20μPa, which is absolute silence. For comparison, normal breathing has a sound pressure of around 60μPa.

There are two thresholds that determine the upper limit of our hearing range. The first is where we start to feel pain, and the second is where the intensity of the sound causes harm to the ear. Understanding these thresholds is crucial to protecting our hearing health.

Inner ear

This part of the ear is hidden from sight, enclosed in a bony labyrinth where the cochlea, semicircular canals and the vestibule are located. When it arrives here, the sound has been attenuated by the middle ear and is ready to be analyzed, transformed and transmitted to the brain, where it will be processed.

‍

Physics of the Ear: Measuring pressure and sound

Our ears are very sophisticated instruments with incredible sensitivity. We can carry out calculations on this range of perception.

Physics of the Ear: From air pressure to decibels

Sound waves are pressure waves, which means that information travels thanks to the alternation of rarefaction and concentration zones of particles in the air.

Pressure is measured in pascals, but the range of pressure levels that we can hear covers a vast range, from a millionth of a pascal to hundreds of pascals. To make it more convenient to describe these levels, we use a logarithmic scale to reduce the excursion range from millions. This scale is known as the decibel, which is an intensity scale used to represent the pressure level of a sound. The decibel is defined with respect to a reference point, which is the softest sound that we can hear.

Using the decibel scale allows us to describe a range of sounds more accurately and conveniently. For example, the threshold of hearing is defined as 0 decibels, while the threshold of pain is around 120 decibels. By using this scale, we can better understand the intensity of sounds and take steps to protect our hearing health when necessary.

Lp=20 log (p/p0), P0=20μPa

Where Lp is the pressure level relative to the pressure p, and p0 is the reference pressure. Let's take an example: we want to know the pressure level corresponding to 20Pa:

p=20Pa

Lp=?

Lp=20 log (p/p0)=20 log (20/20·10-6)=20 log 106=120dB

Lp=20 log pp0=20 log 2020·10-6=20 log 106=120dB

We say that 20Pa corresponds to 120dB SPL. SPL stands for sound pressure level to indicate we're talking about sound since the logarithmic scale has many uses.

Figure 3.- Decibel scale showing the noises we usually hear and their normal range. It also shows the sensations we have for every scale, Camacho - Study Smart Originals

The same evolutionary processes that shape the human hearing system are the ones that constrain the range of frequencies we can capture. The range of sound we can hear is the result of this process.

Consequences of damage to the ear

The ear is a complex and delicate system that is highly adaptive but can also be susceptible to damage. One of the most common issues is hearing loss, which can occur naturally with age or as a result of exposure to loud sounds. Loud sounds can cause damage instantly or gradually over time, leading to more severe hearing loss. Tinnitus is another malfunction of hearing that can be caused by exposure to loud noises and is characterized by hearing sounds such as ringing or hissing where there is no external cause for the sound.

The inner ear is responsible for balance as well as the perception of sound. The vestibular system, which includes the semicircular can

Physics of the Ear

What is the physics behind the human hearing process?

The human hearing process converts the mechanical waves of sound into an electrical signal by using sensitive cells inside the ear.

How can our ears detect sound waves physics?

Sound travels to the outer part of the ear where it is focused into the ear canal and then transmitted to the inner ear. The inner ear then provides a way to convert these mechanical movements into electrical signals that are sent to the brain.

Why is human hearing limited?

The same evolutionary processes that shape the human hearing system are the ones that constrain the range of frequencies we can capture. The range of sound we can hear is the result of this process.

What are the 3 bones located in the ear for hearing?

The three bones located in the ear for hearing are Malleus, incus and stapes

‍