How your hearing works

How do we hear?

Although very complex here is a simplified version.

The ear although very handy for hanging glasses or earrings does a very specific task. The pinna acts like a funnel to collect and direct sound vibrations down the ear canal to the eardrum. Whilst doing this the vibrations that are the most important are slightly increased.

The canal also protects the eardrum from damage. Sound vibrations reach the eardrum causing it to vibrate.

Sound is now changed to mechanical energy, at the back of the drumhead there are tiny bones (the smallest in the body! the malleus, incus and stapes) that move with a lever motion.

The energy passes through these bones and reaches the cochlear. This is a small cavity which resembles the shell of a snail. Inside there are tiny hairs (cillia) and fluid.

Once inside the energy causes a vibration within the fluid and it is this movement that causes the hair cells to move. When the hair cells move they trigger an electrical impulse to the brain.

Which hair cells have been stimulated depends upon the frequency of the sound. The first turn of the cochlear is responsible for high frequency sounds, the mid turn for the mid frequencies and the last turn (apex) for the low (Bass) frequencies.

The electrical impulse travels along the auditory nerve to the brain, which interprets the impulses.

Who can benefit from a stereo hearing system?

Scientific research as well as individual experience confirms that most people with a hearing loss in both ears would benefit from having two hearing instruments, even if the hearing loss is mild. There are a few isolated cases where this is not so – your hearing care professional or physician can advise you.

Sound localization

The ability to localize sound is dependent on two properly functioning ears. How do we know the direction of a car’s approach? The sound reaches the closer ear a few micro-seconds earlier, and with a somewhat greater intensity, than it reaches the other ear. These minute differences in the signal transferred from the ear to the brain enable us to make important, potentially life-saving decisions regarding the exact location of the car. When one ear functions better than the other, there is inadequate information to quickly and reliably determine the origin of a sound.

Understanding speech in a noisy environment

Hearing with two ears provides improved capacity to suppress background noise, making it easier to understand conversation.

Unequal hearing in the left and right ears is a big disadvantage in noise. While one hearing instrument may be helpful in noisy situations. The greatest difficulty understanding speech occurs when several people are talking at once. This is common during interactions between family, friends and colleagues at work. Often these exchanges are also taking place in noisy surroundings. With two hearing instruments it is possible to maximize understanding in noise.

Hearing with less volume

A sound presented to both ears is judged to be louder than the same sound, at the same intensity, presented to only one ear. This means that a user of two hearing instruments can set the volume of each one lower, resulting in more pleasant hearing and less amplification of distracting background noises.

Hearing equally from both sides

Wearing two hearing instruments gives the maximum opportunity to respond accurately and confidently, whether the conversation comes from the left or right.

The hearing threshold

For us to be able to hear a sound at all, it needs to be above a certain level. This is called the hearing threshold or auditory threshold.

Human beings have a threshold of around 0 decibels, and above this level, sounds that have higher sound pressure levels are heard as louder noises.

Hearing can become uncomfortable if the sound pressure level is above 110 decibels (typical discomfort level), and it becomes painful above 130 decibels (typical pain threshold).

The image to the right shows different levels of hearing thresholds.