A healthy young human ear can detect sound frequencies from roughly 20 Hz to 20,000 Hz (20 kHz), a span of about ten octaves. That textbook range, though, is more of a best-case ceiling than a lived reality. Sensitivity varies enormously across those frequencies, and the boundaries themselves are softer than they appear: infrasound below 20 Hz is audible when it’s loud enough, and ultrasound above 20 kHz can reach the brain through bone conduction. Age, noise exposure, sex, and individual anatomy all redraw the map for each person.
How the Ear Sorts Sound by Frequency
The cochlea, the snail-shaped structure in your inner ear, acts as a kind of frequency analyzer. It’s lined with a membrane whose physical properties change along its length. High-frequency sounds vibrate the narrow, stiff portion near the entrance (the base), while low-frequency sounds travel deeper and vibrate the wider, more flexible end (the apex). This arrangement creates a frequency map, called tonotopy, that follows an almost-exponential curve from base to apex.
1PubMed Central. Three-dimensional tonotopic mapping of the human cochlea based on synchrotron radiation phase-contrast imagingThe idea that specific places along the cochlea correspond to specific frequencies dates back centuries, but physiological confirmation came in stages. Electrical recordings of the ear discovered in 1930 matched the pattern, and later physical observations of anatomical specimens confirmed that high-intensity sound spreads its effect more broadly through the cochlea, especially for low-frequency tones.
2PubMed Central. The Developing Concept of Tonotopic Organization of the Inner EarThis place-based coding isn’t the ear’s only trick. Auditory nerve fibers also carry timing information, firing in sync with the peaks of a sound wave. Researchers have debated for decades whether pitch perception relies more on where the cochlea vibrates or on when nerve fibers fire. The current consensus is that both mechanisms contribute, and the relative importance shifts depending on the frequency. In cochlear implant users, where fine timing information is poorly transmitted, the difficulty perceiving music and pitch contours in speech highlights how much timing cues normally add.
3PubMed Central. Revisiting place and temporal theories of pitchWhere You Hear Best Within the Range
Even within the 20–20,000 Hz window, sensitivity is wildly uneven. Your ear is not a flat-response microphone. It is most sensitive to frequencies in the 1,000–5,000 Hz range, the zone where most speech consonants live. At both the very low and very high ends of the range, sounds need to be much louder before you can hear them at all. The equal-loudness contours standardized by the International Organization for Standardization (ISO 226) map this uneven sensitivity in detail, and the familiar “A-weighting” used in noise measurement is essentially an approximation of how the ear responds at moderate loudness levels.
4The Journal of the Acoustical Society of America. The dB[EQL]: An alternative sound pressure weighting according to the equal loudness contours of the international standard ISO 226-2003Part of this sensitivity boost comes from the ear canal itself. The canal acts like a short resonant tube that amplifies certain frequencies before they even reach the eardrum. One study measuring sound pressure inside and outside the ear found that the canal boosted levels by several decibels, with the peak amplification shifting depending on the loudness of the incoming sound. At moderate levels, men showed the biggest boost around 2,000 Hz, while women showed it around 8,000 Hz. At higher sound levels, both sexes saw the largest amplification at 8,000 Hz.
5PubMed Central. Acoustical role of ear canal in exposure to the typical occupational noise levelsThese differences matter more than they might seem. Because the ear canal isn’t perfectly standardized across people, two individuals exposed to the same sound in the same room may actually experience different sound pressure levels at the eardrum. Noise exposure guidelines, hearing protection ratings, and audiometric measurements all implicitly assume a “standard” ear canal, which is one reason individual results can vary from the textbook numbers.
Below 20 Hz: Infrasound Is Not Inaudible
The 20 Hz lower boundary gets repeated so often that many people assume sounds below it are physically impossible to hear. That’s not quite right. Infrasound, defined as sound below 20 Hz, is audible if the level is high enough. The ear’s sensitivity drops off steeply at very low frequencies, so an infrasonic tone might need to be 90 or 100 decibels louder than a midrange tone to reach the hearing threshold, but it can get there.
6PubMed. Hearing at low and infrasonic frequenciesThis has been confirmed experimentally. In a study measuring hearing thresholds and perceived loudness for infrasonic frequencies, all participants could hear the infrasound when the level was sufficient. They also reported sensations beyond hearing, such as pressure in the ear, headache, and vibrations felt in other parts of the body. Those additional sensations appeared both below and above 20 Hz, which undercuts the idea that infrasound is fundamentally different from “regular” sound.
7Applied Acoustics. Hearing threshold, loudness, and annoyance of infrasonic versus non-infrasonic frequenciesSources of infrasound in everyday life include wind turbines, heavy traffic, industrial machinery, and natural phenomena like ocean waves and earthquakes. Most of these produce levels well below the point where you would consciously hear them, but in occupational settings or near large machinery, infrasonic levels can climb into audible territory. At levels somewhat above the hearing threshold, the ear remains the primary organ for sensing infrasound, though you can also feel vibrations through the chest and skull.
6PubMed. Hearing at low and infrasonic frequenciesAbove 20 kHz: Ultrasound Through Bone
The upper boundary is more complicated than the lower one. Through normal air conduction (sound waves entering the ear canal), most adults lose the ability to hear anything above roughly 16–18 kHz well before old age, and even young children rarely perceive much beyond 20 kHz through air. But when sound is delivered through bone conduction, pressing a vibrating transducer against the skull, humans can perceive frequencies far into the ultrasonic range.
8PubMed Central. Perception Mechanism of Bone-Conducted Ultrasound and Its Clinical UseBone-conducted ultrasound has been studied at frequencies up to 30 kHz and beyond. Research involving participants exposed to bone-conducted ultrasound at 27, 30, and 33 kHz confirmed that the cochlea’s basal turn, the region nearest the entrance that normally handles the highest audible frequencies, is involved in processing these signals.
9PubMed. Human ultrasonic hearing is induced by a direct ultrasonic stimulation of the cochleaEven air-conducted ultrasound, which most people can’t consciously hear, may not pass through the brain entirely unnoticed. One neuroimaging study found that ultrasound presented through the air at levels below the participant’s conscious hearing threshold still produced measurable brain activation, particularly in areas involved in cognitive control.
10PubMed Central. Air-conducted ultrasound below the hearing threshold elicits functional changes in the cognitive control networkWhether this subconscious processing has any meaningful effect on health or behavior remains unclear. A pilot study that exposed participants to airborne ultrasound over a longer period found regional gray matter changes in certain frontal brain areas, though the behavioral consequences were uncertain.
11PubMed Central. A longitudinal, randomized experimental pilot study to investigate the effects of airborne ultrasound on human mental health, cognition, and brain structureThis is an active area of concern because ultrasonic emitters are increasingly common in everyday technology, from motion sensors and pest repellers to cleaning equipment and industrial processes. The research is too early-stage to draw firm conclusions about harm, but it does put a dent in the assumption that sounds above 20 kHz are irrelevant to humans.
How Age Reshapes Your Hearing Range
The most reliable predictor of which frequencies you can hear is how old you are. High-frequency hearing erodes steadily with age, a process called presbycusis. A typical 50-year-old has already lost much of the ability to hear above 12–14 kHz; by 65 or 70, frequencies above 8 kHz may be gone. The loss starts at the top of the range and creeps downward, which is why age-related hearing trouble usually shows up first as difficulty hearing consonants (which carry more high-frequency energy) rather than vowels.
The cellular story behind this loss centers on the sensory hair cells inside the cochlea. These microscopic cells convert mechanical vibrations into nerve signals, and once they die, mammals cannot regrow them. Research using human temporal bone specimens has shown that hair cell degeneration in aging humans is dramatically worse than in aging laboratory animals, which suggests that much of what we call age-related hearing loss actually reflects the accumulated damage of a lifetime of noise exposure rather than pure biological aging.
12PubMed Central. Age-Related Hearing Loss Is Dominated by Damage to Inner Ear Sensory Cells, Not the Cellular Battery That Powers ThemThat’s a surprisingly hopeful finding, because it implies much of the loss is avoidable. Animals raised in quiet environments keep their high-frequency hearing far better than humans do. Chronic noise exposure at work, in traffic, through headphones, and at concerts gradually destroys the very hair cells at the cochlear base that handle the highest frequencies.
The 4 kHz Notch and Noise Damage
Noise-induced hearing loss doesn’t erase frequencies uniformly. It tends to carve out a characteristic dip in your hearing ability centered around 4,000 Hz, with partial recovery at 8,000 Hz. On an audiogram, this looks like a notch or valley, and audiologists consider this shape a hallmark of noise damage.
13Ear and Hearing. The Significance of Audiometric Notching in Individuals With a History of Noise Exposure: A Systematic ReviewWhy 4 kHz in particular? The ear canal’s resonance amplifies frequencies in the 2–4 kHz range before they reach the cochlea, so the hair cells responsible for those frequencies receive a slightly higher dose of energy for any given external sound level. Over years, that extra dose adds up. The 4 kHz notch is so closely associated with noise exposure that it’s commonly used to distinguish noise damage from other causes of hearing loss on clinical audiograms, although the distinction isn’t always clear-cut in older patients whose age-related loss has caught up to the notch.
Sex Differences in Hearing Ability
Men and women lose hearing at different rates. Data from the Baltimore Longitudinal Study on Aging found that hearing ability declined more than twice as fast in men compared to women at most ages and frequencies tested, with the disparity being especially pronounced at higher frequencies. Men also tend to develop age-related hearing loss earlier and more often.
14PubMed Central. Sex-Based Differences in Hearing Loss: Perspectives from Non-Clinical Research to Clinical OutcomesSome of this gap is likely explained by differences in occupational noise exposure: historically, men have been more heavily represented in noisy industries like construction, manufacturing, and military service. But animal studies also show sex-based differences in hearing loss trajectories even when noise exposure is controlled, suggesting that hormonal or genetic factors play a role too. Estrogen, for example, appears to have some protective effect on cochlear hair cells, though the exact mechanisms are still being worked out.
The practical upshot is that a 60-year-old man and a 60-year-old woman sitting in the same room are likely operating with somewhat different hearing profiles, especially above 2 kHz. Hearing aid fitting, noise exposure guidelines, and screening recommendations ideally should account for this, though in practice, many guidelines still treat the sexes identically.
Telling Frequencies Apart vs. Detecting Them at All
There’s a difference between being able to hear a frequency and being able to distinguish it from a nearby frequency. You might detect both a 3,000 Hz and a 3,050 Hz tone at normal volumes, but whether you perceive them as two different pitches is a separate question. This frequency discrimination ability also changes with age, and not evenly across the range.
A study comparing younger and older adults with clinically normal hearing found that frequency discrimination thresholds were about 2.4 times worse for the older group at 4,000 Hz, but only about 1.2 times worse at 500 Hz. The basal (high-frequency) region of the cochlea took the bigger hit, with detection thresholds nearly four times worse in older participants than in younger ones.
15Heliyon. Age-related differences in local and broadband frequency perception in typically hearing adultsThis means an older person can often still hear high-frequency sounds at sufficient volume but can’t tell them apart as well. In practical terms, that shows up as difficulty following speech in noisy environments: the consonants are loud enough to hear, but the subtle pitch differences that help separate one speaker from background chatter become blurred. A standard hearing test, which only checks whether you can detect a tone, may not catch this kind of degradation.
When Lost Frequencies Generate Phantom Sound
Tinnitus, the perception of sound in the absence of any external source, is closely tied to the frequencies you’ve lost. The brain appears to compensate for missing input from damaged hair cells, and the phantom tone it produces tends to match the region of hearing loss. Research has found a strong correlation between the “edge frequency,” the point on an audiogram where hearing drops off sharply, and the pitch that people with tinnitus perceive.
16PubMed. The relationship between tinnitus pitch and the edge frequency of the audiogram in individuals with hearing impairment and tonal tinnitusTwo models compete to explain this. One proposes that hearing loss causes the brain’s frequency map to reorganize: neurons that used to respond to the lost frequencies get reassigned to respond to neighboring frequencies, and that reorganization generates a phantom signal. The other model suggests that increased synchronization among neurons in the hearing-loss region creates the perception of a tone.
17PubMed Central. Tinnitus Is Associated With Extended High-frequency Hearing Loss and Hidden High-frequency Damage in Young PatientsIn young tinnitus patients, extended high-frequency audiometry, which tests beyond the usual 8 kHz cutoff, often reveals damage that standard audiograms miss entirely. The tinnitus pitch in these cases falls within the area of high-frequency hearing loss, even when the standard test looks clean. This has led researchers to argue that conventional audiograms, which typically stop at 8 kHz, underestimate how many young adults already have significant hearing damage.
17PubMed Central. Tinnitus Is Associated With Extended High-frequency Hearing Loss and Hidden High-frequency Damage in Young PatientsWhy Humans Hear This Range and Not Another
The 20–20,000 Hz window isn’t arbitrary. It reflects a long evolutionary history shaped by the anatomy of the mammalian middle ear and cochlea. The earliest mammalian cochleae were only about 2 mm long and included a structure called the lagena macula that is now absent in most modern mammals. Comparisons of fossil and living species suggest that true high-frequency hearing above 20 kHz wasn’t achieved until around 125 million years ago, during the early Cretaceous period, as middle ear bones became smaller and more efficient at transmitting high-frequency vibrations.
18PubMed Central. Evolutionary paths to mammalian cochleaeMany modern mammals pushed far beyond the human upper limit. Bats and dolphins routinely use frequencies above 100 kHz for echolocation, and mice hear well into the 80–90 kHz range. Humans, along with other great apes, settled on a hearing range optimized for communication at moderate distances in open and semi-forested environments, with peak sensitivity in the frequency band most useful for distinguishing speech sounds and detecting the rustling or snapping noises that signal predators or prey. We traded ultrasonic acuity for a brain that could extract extraordinarily detailed meaning from a narrower frequency window, which, depending on your perspective, worked out reasonably well.