Have you ever wondered about the range of sound frequencies that the human ear can detect? Often, we come across claims that we can hear sounds only in the frequency range of 20Hz to 20kHz, but is it completely accurate? Is it possible to hear sounds beyond the 20kHz limit?
As a general rule, most humans cannot hear audio over 20kHz. The average human hearing range is from 20Hz to 20kHz. However, some people claim to hear higher than 20kHZ.
This is a raging debate within the audiophile community, and to date, no absolute study confirms or denies that 20kHz is the upper limit. If someone says that they can hear above 20kHz, who are we to say they can’t?
From a speaker designer’s perspective, working in the audio industry actively designing audio products, this is a very interesting question. When we design a speaker, we only consider the listening range of between 20Hz to 20kHz; however, when completing audio simulations, I have found that it can be useful to look at modes and acoustic responses above 20kHz, as this could “colour” or influence the sound of music in the hearing range.
I am not saying I (or anyone else) can hear above 20kHz. However, because there is still audio activity above 20kHz, if we see distortion or interesting artefacts in speaker simulations above 20kHz, it can help us debug or consider what is happening in the listening range. (i.e. below 20kHz)
In this article, I will delve into the fascinating science of audio frequencies, exploring the upper and lower limits of human hearing.
I need to point out that I am not a medical expert. My interest in this topic is from the perspective of an audio engineering designer.
Can You Hear Audio Over 20kHz?
It is widely accepted that most humans, especially those beyond the age of 20, cannot hear audio over 20kHz. This phenomenon is a result of presbycusis or age-related hearing loss, which causes a decrease in the ability to perceive higher frequencies. Yet, there are exceptions.
Some children and teenagers can perceive sound in this frequency range, a capacity that tends to diminish with age due to exposure to loud noises and natural ageing processes. While some people claim to hear sounds above 20kHz, it is important to stress that this is far from the norm — and often, what they’re hearing is the byproduct of lower, more audible frequencies.
Therefore, while it’s theoretically possible to hear audio over 20kHz, it’s highly unlikely for most of the population.
Some academic research suggests that we can at least “perceive” something different when exposed to frequencies about 20kHz. [source]
As per research conducted by some scholars, although the explicit hearing of frequencies above 20kHz might not be possible for the majority, there are indications that we can “perceive” these frequencies in a different manner.
These perceptions may not be in the form of traditional “hearing” but rather as a sensation of pressure or a feeling of “presence”. Certain studies point out that these frequencies might interact with our auditory system, leading to the sensation of sound even if it’s not “heard” in the conventional sense.
It is for this reason that I personally look at audio frequencies above 20kHz when simulating a speaker design to see if there is anything interesting going on above this range which might impact how we perceive sound.
It’s an intriguing notion that our body might have the ability to sense these high frequencies even if we can’t audibly discern them. However, much more research is required to explore this fascinating avenue of auditory perception.
Why Can’t Humans Hear Above 20kHz?
The limitation of human hearing above 20kHz is a consequence of the physiology of our ears, specifically, the structure of the inner ear known as the cochlea.
The cochlea is a spiral-shaped organ filled with fluid and lined with thousands of tiny hair cells. When sound waves enter the ear, they cause the fluid in the cochlea to ripple, which in turn stimulates the hair cells. These hair cells then transform the mechanical energy into electrical signals that the brain interprets as sound.
However, the ability of these hair cells to respond to sound waves diminishes with increasing frequency. This is because the hair cells that perceive high-frequency sounds are located near the entrance of the cochlea, where they are most susceptible to damage. Continuous exposure to loud noises and the natural ageing process can lead to the loss of these delicate cells over time, thereby reducing our ability to hear sounds in the higher frequency range.
Furthermore, even in a perfectly healthy ear, the mechanical properties of the cochlea and its fluid prevent it from effectively transmitting sounds above 20kHz. This physiological limitation, combined with the potential for damage and loss of high-frequency hair cells, explains why most humans cannot hear sounds above 20kHz.
This is one of the many reasons cited as to why humans cannot hear about 20kHz – simply because there is a physical barrier to it. However, as mentioned, many still claim to hear above this range.
Of course, if we factor in bone conduction technology, then it is argued that we can hear above 20kHz, as with bone-conducting headphones, you hear sound through bone conduction technology, which bypasses our ears. [source]
What Is The Lowest Frequency A Human Can Hear?
On the lower end of the scale, the average human ear can detect frequencies as low as 20Hz. These low-frequency sounds are often felt more as vibrations rather than heard as actual sounds. This is because the human ear is less sensitive to these frequencies, and our ability to perceive them is greatly affected by environmental conditions and the presence of background noise.
For instance, in a quiet room, you might be able to hear a 20Hz tone, but if you’re out in a busy city street, the ambient noise would likely drown it out.
Moreover, just as with the upper limit, the lower limit of our hearing can also be affected by age and exposure to loud noises, which can cause damage to the hair cells in our ears that respond to low frequencies.
Why Can’t Humans Hear High-Frequency?
As mentioned, the inability of humans to hear high-frequency sounds is primarily due to the physical and physiological constraints of the human ear.
Sound is perceived when the hair cells within the cochlea, a part of our inner ear, are stimulated by sound waves and send electrical signals to the brain.
High-frequency sounds are detected by hair cells located near the beginning of the cochlea, making them the first to encounter incoming sound waves and, thereby the most vulnerable to damage.
Over time, these cells can be damaged by exposure to loud sounds or simply deteriorate due to ageing, reducing our ability to perceive high-frequency sounds.
Moreover, the cochlea’s structure and the fluid within it have specific mechanical properties that limit its ability to transmit high-frequency sound waves effectively. Thus, even under ideal conditions, most humans cannot hear sounds much above 20kHz.
The auditory spectrum of humans is fascinatingly complex and uniquely limited. Although we can theoretically perceive sounds ranging from 20Hz to 20kHz, our capacity to hear these extremes is influenced by several factors, including age, exposure to loud sounds, and the physical conditions of our auditory system.
We may not be able to hear frequencies above 20kHz or below 20Hz in a conventional sense, but our bodies can interact with these frequencies in intriguing ways — from feeling a subtle vibration to sensing a distinct presence. For those of us who design audio products, this is important to know.
The mysteries of human hearing continue to provoke scientific curiosity, and further research into this field may unravel even more about our interaction with the world of sound.