INTERACTIVE EXPLANATION

How does a sound reach your brain?

Start with a vibration. Follow air, eardrum, tiny bones and hair cells, then see why the message reaching your brain is a different kind of signal.

Enable JavaScript to change the conditions and run the interactive experiment.

Make a discovery

A sound wave travels through air while nearby air particles move back and forth. Hearing then converts that mechanical vibration into a nerve signal. The wavy graph is a measurement picture—not the path the air travels.

Make a prediction

When sound travels to the right, does the highlighted air parcel travel all the way to your ear?

Yes, it rides with the wave
No, it moves back and forth locally

Read the explanation

The disturbance travels; the parcel oscillates near its original position in this small-amplitude model. Watch the gold marker while the pressure pattern moves past it.

Understand it

A disturbance moves onward

In this plane-wave model, air displacement is along the direction of travel. Compressions and rarefactions are regions of slightly higher and lower pressure. The gold marker follows one representative air position so you can see it oscillate without traveling across the whole room.

From eardrum to inner ear

Sound in the ear canal vibrates the eardrum. Three middle-ear bones—malleus, incus and stapes—transmit the motion into cochlear fluid. They help couple airborne sound into the fluid-filled inner ear.

A place becomes a signal

A traveling wave moves the basilar membrane. Different regions respond most strongly to different frequencies: high frequencies near the base, low frequencies toward the apex. Hair-cell transduction produces electrical signals that reach the brain through the auditory nerve.

Look closer at the science

A reference map for the cochlea

Greenwood’s organ-of-Corti approximation uses f = 165.4 × (10^(2.1x) − 0.88), where x is fractional distance from the apex. The unfolded view reverses that coordinate so base is at the left. It is a reference relationship: anatomy varies, sound level affects responses, and the drawn motion envelope is illustrative.

Frequency and wavelength

For the chosen uniform medium, c = fλ. We fix c = 343 m/s as an illustrative air value near room temperature. Doubling frequency halves wavelength. Actual sound speed depends on the medium and conditions.

Displacement is not pressure

The visual uses ξ(x,t) = A cos(kx − ωt). Compression follows −∂ξ/∂x, giving a sine-shaped pressure variation a quarter cycle from displacement. Here k = 2π/λ and ω = 2πf. Particle displacement is magnified and playback is slowed 400×.

Amplitude is not a hearing test

The amplitude setting is a relative displacement scale, not decibels at your ear. Larger amplitude generally means greater sound intensity in the same linear medium. Perceived loudness and pitch involve the listener as well as the physical wave; no hearing threshold is estimated.

Try it yourself: Feel a gentle vibration

Supplies

Your voice, if comfortable
Paper and a pencil

Notice silence
If comfortable, rest fingertips lightly on the front of your throat without pressing. First remain silent. You can skip touch and simply draw the wave model instead.
Hum gently
Hum briefly at a comfortable, ordinary volume. Notice the vibration beneath your fingers. Stop humming and compare. Do not press your throat or try to make the loudest sound.
Separate source and receiver
Sketch voice vibration → air pressure wave → eardrum → inner ear → nerve signal. Your observation was at the source; it did not measure the motion inside the ear.

What changes when a vibration starts and stops?

Optional gentle observation. No loud sounds, headphones or hearing tests. Feeling vibration is not a measurement of vocal-fold motion or frequency.

Sources and model limits

One-dimensional plane wave, no attenuation, reflections or three-dimensional spreading. Air markers are sample parcels, not a molecular-dynamics calculation.
The unfolded ear and magnified close-ups are functional schematics, not an anatomical section. The basilar-membrane place marker uses the approximate human Greenwood map; it is not a personal pitch map, an implant map or a cochlear fluid solver.
The animation shows an established continuous tone, not an onset/transit-time experiment. Ear-part motion and neural pulses are qualitative; the air wave alone uses the stated equation. The simulation is silent, with no loudness or medical assessment.

The Greenwood relationship approximates human organ-of-Corti frequency and position; it is distinct from a neural spiral-ganglion map.

Stakhovskaya et al. (2007), Frequency Map for the Human Cochlear Spiral Ganglion, restates Greenwood’s human coefficients and explicitly distinguishes the two anatomical maps. Greenwood (1990) is the original reference. Used for a reference marker only, not neural response prediction.

Stakhovskaya et al. · Cochlear maps

Hair-cell electrical responses lead to chemical transmission at the afferent synapse.

Ottersen et al., Molecular organization of a type of peripheral glutamate synapse (1998). The inner-hair-cell synapse and postsynaptic receptors support the distinction between transduction, transmitter release and nerve activity. No microscopic image is copied.

Ottersen et al. · Hair-cell synapses

Voice production involves vibrating vocal folds and resonating air passages.

NIDCD, Taking Care of Your Voice, What is voice? and Use your voice wisely. Supports the source-to-air connection in the optional gentle observation; this adapted procedure has not been trialed with learners.

NIDCD · Voice & vibration

Sound in air is longitudinal; displacement and pressure have different spatial phases.

University Physics Volume 1 §17.1, Fig. 17.3 and Eqs. 17.1–17.2. Supports particle displacement and pressure graph alignment.

OpenStax · Sound waves

Sound speed depends on medium and temperature.

University Physics Volume 1 §17.2. 343 m/s is a fixed teaching value, not a room measurement.

OpenStax · Sound speed

Eardrum motion passes through ossicles to cochlear fluid, hair cells and auditory nerve signals.

NIDCD, How Do We Hear?, numbered sequence 1–6. Supports functional pathway and high/low cochlear-place distinction.

NIDCD · How we hear

Loud sounds can damage hearing.

NIDCD, Noise-Induced Hearing Loss. Supports silent visualization and gentle, optional observation without headphone or volume targets.

NIDCD · Hearing protection

Independent subject review is pending.

Read the sources and model assumptions