Science, Art, Litt, Science based Art & Science Communication

Different people hear sounds differently!

Q: Do different people hear sounds differently?

Q: Why do some people fear the sound of fire crackers?

Q: Why do some people hate loud music while some love it?

Krishna: Humans have two ways of perceiving sound. The first involves the process of sound vibrations travelling through the middle ear to the inner ear, which is where they are transmitted to the brain. The other relies on sound being conducted through bones in the skull, a process known as bone conduction. Most people don't know that our skull also transmits sound to our brain and the way people perceive sounds depends on the individual's skull structure.

Sound, transmitted as vibrations through the skull, travels to the temporal bone, which is situated at the sides and base of the skull. The temporal bone transmits the vibrations to the basilar membrane in the inner ear and tiny bundles of hair, each finely tuned to detect sounds at different frequencies, transmit the vibrations to the brain for decoding.

Many of us feel odd somewhat when we play back a recording of our own voice because a recording sounds differently. Vibrations are heard directly by the inner ear bypassing your eardrums. In fact, this is one of the ways we hear your own voice and therefore perceive our voice differently to how others hear it. Interestingly, bone conduction plays a role in how we recognise our voice. This is because the process is more effective at transmitting lower frequency sounds to the brain, which means that we perceive our voice as being deeper, lower and fuller than what it is.

There is an interesting story: Ludwig van Beethoven, the famous 18th century composer who was almost completely deaf, discovered Bone Conduction(we can't confirm this story). Beethoven found a way to hear the sound of the piano through his jawbone by attaching a rod to his piano and clenching it in his teeth. He received perception of the sound when vibrations transfer from the piano to his jaw. This has proven at that time that sound could reach our auditory system through another medium besides eardrums and the other medium is our bones.

Otoacoustic emissions can involve bone conduction which makes different people hear sounds differently depending on their skull's shape. Some people hear sounds very loudly while some hear the same sounds at tolerable levels.

Bone conduction transmission occurs constantly as sound waves vibrate bone, specifically the bones in the skull, although it is hard for the average individual to distinguish sound being conveyed through the bone as opposed to sound being conveyed through air via the ear canal. Bones generally convey lower-frequency sounds better than higher frequency sound.

Some symphony or concert halls, are known to beautifully reflect the sounds of an orchestra. It turns out there’s a similar process at play in your cochlea, deep inside your ear—where a tiny bony cavity houses the organ that allows you to hear. It’s like its own tiny little acoustics chamber. So anything and everything you hear is going into our ear and then going into this little bony chamber.

There’s actually a lot of variability in the way people hear. Some frequencies can appear tens of decibels louder or quieter than average—based on the resonant properties of a person’s skull. The skull itself, because it’s such an intimate and personal thing, is going to shape your experience of the world, perceptually (1).

This bone conduction of sound is being used by scientists to make the deaf hear now.

Most cases of hearing loss are due to damages to the eardrums. Since bone conduction does not use the eardrums, people with hearing difficulties would be able to hear clearly again with bone conduction, provided that their cochlea is in healthy and normal condition.

Generally, hearing loss could be described into three categories. That would be conductive hearing loss, perceptive hearing loss and mixed hearing loss. Conductive hearing loss is associated with faulty transmission of sound and is mostly due to damages to the eardrums. Bone conduction is able to aid a conduction hearing loss because a bone conduction device performs the role of the eardrums. Perceptive hearing loss is associated with difficulty in sensing the vibrations by the auditory nerves at the cochlea. Bone conduction is less effective for perceptive hearing loss. As for mixed hearing loss, it is best to suggest a trial in advance to find out whether bone conduction could be an aid to mixed hearing loss because it differs among individual.

Some hearing aids employ bone conduction, achieving an effect equivalent to hearing directly by means of the ears. A headset is ergonomically positioned on the temple and cheek and the electromechanical transducer, which converts electric signals into mechanical vibrations, sends sound to the internal ear through the cranial bones. Likewise, a microphone can be used to record spoken sounds via bone conduction.

Citations:

1. https://asa.scitation.org/doi/10.1121/1.5124321