The human ear is an intricate example of miniature and sophisticated engineering. Scripture is clear about its origin: ‘The hearing ear, and the seeing eye, the Lord has made them both’ (Proverbs 20:12).
Note the dual stress upon the hearing ear and the seeing eye, implying a marvellous system in operation. It invites readers to investigate further.
The way we hear
Sound is a pressure disturbance in the air such that small cyclical vibrations of pulsing pressure (called acoustic waves) travel into the ear canal and reach the eardrum at the end of the auditory canal. This is called the tympanic membrane (see Fig. 1).
The small vibrations of the tympanic membrane transfer through tiny ossicle bones into the inner ear. Each stage of this system is staggeringly complex.
All mammals have a system which carry acoustic waves through an eardrum and ossicle bones into the inner ear (see Fig. 2). However, there are large differences among mammals. Certain lengths of tubes will vibrate at different frequencies. To give a man-made example, a flute will change its natural frequency depending upon which keys are pressed open.
The human ear canal is about 2 cms long. In cats and dogs, the ear canal has a bent shape. They have a vertical and horizontal ear canal, designed for a different range of frequencies.
Humans can hear a wide frequency range, from approximately 20 to 20,000 hertz (Hz), equivalent to nine octaves. Dogs hear from approximately 65Hz – 44,000Hz, while cats’ range is from 55Hz to 77,000Hz. Our ears are designed for low frequency as well as high frequency sound, resonating in the range of 4,000Hz (ideal to comprehend human speech).
Human ears are such that we begin to lose perception of higher frequencies (12,000+Hz) while in our twenties.
The fundamental frequency range is from 125 to 400Hz, but what is called the ‘harmonics’ of the vibration (multiples of the fundamental) extend the frequency range of human speech. In particular, the human voice carries with it a raft of harmonics which means that any voice is unique for each individual.
This includes the voice of Christ himself, which all creation obeys. He demonstrated this in Mark 4, when he commanded the wind and the waves to obey him. It was indeed the same voice which spoke all things into existence at creation!
The harmonics of the human voice are particularly important in the region of 2000Hz to 5000Hz. It is in this region that different vowel sounds are distinguished. What is remarkable is that the ear canal is just the right length to resonate (vibrate in sympathy) with these frequencies.
The voice of many waters
It has been shown that all sounds produced by water arise from the popping of tiny bubbles. Each bubble vibrates at a different frequency, depending on its size, and so a range of frequencies is heard as water flows and the popping bubbles produces vibrations.
The sound of a babbling brook, a flowing waterfall or a crashing ocean wave are made by billions of tiny air bubbles vibrating against the mass of the water surrounding them.
These countless bubbles all have a slightly different frequency but all lie exactly within the range that the human ear amplifies by the acoustic resonance provided by the ear canal. Indeed, who has been unmoved by the gentle lilt of a sparkling stream, the majestic roar of ocean waves or the relentless hammering of a rainstorm?
These same frequencies also occupy the region where human speech is distinctive. It is therefore no wonder that the Bible says, ‘The voice of the Lord is upon the waters: the God of glory thunders: the Lord is upon many waters’ (Psalm 29:3). No word is present in Scripture by accident. God does communicate through his creation, though clarity and precision of his voice are found in the Bible.
The frequencies of birdsong also suit the range of human hearing. This remarkable ability of the human ear canal to resonate and amplify the frequencies of human speech, flowing water and birdsong is a strong witness to the design inherent in our bodies.
The middle ear – ossicle bones
An acoustic signal causes the eardrum to vibrate and push on the malleus (hammer) bone. The malleus then pushes the incus (anvil) bone, which then moves the stapes (stirrup) horizontally (see Fig. 2).
These three bones are known as the ossicle bones and serve to amplify sound. They are tiny (all three could fit on a penny) and are the only bones which are fully formed at birth.
Each of the three bones mentioned are specially shaped to form a lever mechanism which is highly efficient in amplifying sound.
The need to amplify sound signals arises from the fact that they pass from the ossicle bones into a liquid medium in the inner ear.
The inner ear – cochlea
Liquid is a barrier to sound, so the stapes acts like a pump on the oval window membrane. To compensate for the movement of the liquid inside the cochlea, the membrane of the round window (Fig. 3) deftly expands.
If we were to unwind the cochlea (Fig. 4), we would see an ingenious basilar membrane which tapers to register higher frequencies inside the cochlea. It is like a xylophone, so that combined frequencies (arriving from the oval window vibrations) are immediately split up into their component frequencies!
This is effectively an instantaneous frequency analyser. An incoming signal, composed of many frequencies, immediately causes different parts of the basilar membrane to vibrate! Such an ingenious device would make any electrical engineer marvel.
The final part of the hearing system is achieved by the organ of Corti (see detail of Fig. 3), running atop the basilar membrane.
This has tiny little hairs (stereocilia) on it (Fig. 5) which send an electrical signal according to each frequency excited by the incoming signal. Each cilia is only 0.00025 mm thick – less than 1/70th the width of a human hair! It is also astonishing that, when disturbed by the tectorial membrane (which touches the cilia above), a little trapdoor on the cilia opens via a spring attached to an adjacent hair (see Fig. 5)!
This allows electrical ions in the electrically-charged fluid to then excite ganglion nerves which send the signal to different parts of the cerebral cortex in the brain, depending on whether it is music or speech. For low frequencies, there is about one nerve for each change in Hz. In the upper range, it is about 2–3Hz per nerve ending.
Hearing can be damaged by listening to repetitive sounds of one particular frequency (industrial workers without ear defenders are liable to this). Listening to loud music is also detrimental, because the springs at the tip of the cilia can literally snap.
Some people have a genetic defect in their ears such that the cochlea system is not working. However, the brilliant Australian surgeon and professor, Graeme Clark, developed the cochlear implant. This bypasses the system and attaches a microphone to the nerves.
Initially, the procedure enabled basic speech to be heard, but later developments led to implants with greater frequency resolution so that even music could be heard. Such exquisite engineering required clever minds to achieve. The implication is obvious – the original design of the human ear was equally the result of superb intelligent design and forethought!
Such a system involving air vibrations and mechanical, chemical and electrical engineering is truly astonishing. It confirms the intelligent design of the ear. Surely we must echo the glorious truth of Proverbs 20:12 – ‘The hearing ear, and the seeing eye, the Lord has made them both’ and proclaim with the psalmist, ‘I will praise thee; for I am fearfully and wonderfully made: marvellous are thy works; and that my soul knoweth right well’ (Psalm 139:14).
In the light of the wonder of hearing, I trust readers will consider the depth of the miracles of Christ, such as his healing of the deaf man in Mark 7: ‘Then looking up to heaven, he sighed, and said unto him, Ephphatha, that is, Be opened. And straightaway his ears were opened’ (v.34,35).
Consider the profound wisdom of John 18:37 – ‘Every one that is of the truth hears my voice’. We now hear him spiritually, but one day we will hear his voice literally! What a day that will be!
Andy McIntosh is Emeritus Professor of Thermodynamics and Combustion Theory at Leeds University. His research fields include acoustic engineering. The following is an edited extract from ‘Wonders of Creation’ (Day One Publications, 2017).