ARTICLE 1 — IN-DEPTH, SCIENTIFIC & EXPERT VERSION

How bone conduction headphones work: from smartphone to brain

Bone conduction relies on a complete chain, combining digital signal processing, radio transmission, electro-mechanical conversion, vibrational propagationand auditory neurophysiology.
Here is the actual, step-by-step journey from your phone to the conscious perception of sound.

1) From audio content to digital signal: the source (smartphone)

1.1 The sound "in the phone" is not sound

An audio track (Spotify, YouTube, local file) is a sequence of digital information:

Sampling rate: e.g., 44.1 kHz, 48 kHz
quantization (bit depth): e.g., 16 bits, 24 bits
or compression (AAC, SBC, aptX…) depending on the stream.

The smartphone generates a PCM (Pulse Code Modulation) streamas output from the audio system, or a stream already compressed depending on the application and protocol.

1.2 Signal processing (DSP) on the telephone side

Before sending, the phone often applies treatments:

volume normalization,
equalization (EQ),
dynamic compression (for podcasts / voice),
Echo cancellation and noise reduction on calls,
mixing (music + notifications + voice).

This depends on the OS processing, the player, and the call/media mode.

2) Wireless transmission: Bluetooth (from phone to headphones)

2.1 Bluetooth audio encoding (codec)

The phone then encodes the stream into a Bluetooth codec:

SBC (universal standard),
CAA (often on iOS),
aptX/LDAC depending on devices (if supported).

Codec influence:

latency,
bandwidth,
the perceptible quality.

2.2 Radio frequency and reception

The signal is transmitted by radio waves (2.4 GHz).
The headset receives the stream, synchronizes it, and corrects errors (frame mechanisms, buffering) in order to deliver a stable signal despite:

interference (Wi-Fi, crowds, city)
microcouplings,
flow rate variations.

3) Decoding in the headphones: from digital to electrical

3.1 Signal Decompression/Reconstruction

The headset's audio chip:

decode the Bluetooth codec,
reconstructing an audio stream (PCM),
sometimes applies internal treatments (DSP):
- equalization,
- adaptive amplification,
- level limitation (protection).

3.2 Digital-to-Analog Conversion (DAC)

The PCM audio signal is converted into an analog signal via a DAC:

time-varying voltage (waveform),
proportionally to the variations in sound pressure “cable”.

3.3 Amplification and control

Next, an amplifier powers the transducer.
The headset manages:

the gain (volume),
the dynamics,
sometimes a "limiter" to avoid mechanical over-excitation.

4) Bone conduction transducer: from electricity to vibration

4.1 A transducer is not a conventional loudspeaker

In a traditional helmet, a membrane is vibrated to move the air.
Here, the electrical signal is converted into a mechanical vibrationtransmitted to the skull.

The transducer is generally based on:

an electrodynamic actuator (coil + magnet),
or piezoelectric solutions depending on the models.

4.2 Vibration applied to a bony area

The transducer is positioned in an area where:

The bone is close to the inner ear.
Vibrational transmission is effective.
The comfort level remains acceptable.

Typical areas:

zygomatic arch (cheekbone),
temporal region (temporal bone).

Contact pressure is important:
too weak → loss of vibrational energy
Too strong → discomfort and fatigue.

5) Vibroacoustic propagation: from bone to the inner ear

5.1 Bone Conduction: How Energy Travels

Micro-vibrations propagate as mechanical waves through:

skull bones,
adjacent soft tissues.

The skull is not a "uniform block":
It filters, attenuates, and resonates according to:

the frequency,
the support zone,
morphology.

5.2 Bypassing the external and middle ear

The key difference: bone conduction can stimulate the cochlea without going through:

the external auditory canal,
the eardrum,
the chain of ossicles (malleus, incus, stapes).

However, in reality, there is often a mixture:

bone conduction (dominant),
- a little bit of parasitic air conduction (vibration that sets the air in motion near the ear).

6) The cochlea: transformation of vibration into a nerve signal

6.1 Movement of cochlear fluids

When energy reaches the cochlea:

The internal fluids begin to move,
This movement displaces the basilar membrane.

6.2 Frequency analysis (tonotopy)

The basilar membrane acts as an analyzer:

base of the cochlea → high frequencies
peak → low frequencies.

Each frequency stimulates a different area.

6.3 Transduction by hair cells

The inner hair cells convert mechanical movement into nerve impulses:

opening of ion channels,
potential variation,
triggering of electrical signals transmitted to the auditory nerve.

7) From the auditory nerve to the cortex: conscientious perception

7.1 Central transmission

The auditory nerve sends signals to:

brainstem (relay and processing),
inferior colliculus,
thalamus (medial geniculate body),
primary auditory cortex.

7.2 The brain "reconstructs" sound

The brain interprets:

height (frequency),
intensity (volume),
timbre (harmonics),
rhythm and structure.

👉 For the brain, the entry route (air or bone) is secondary: it interprets a nerve signal.

8) The key advantage: layering with ambient sounds

While the headset sends the sound via the bone:

The ears remain open.
Environmental sounds arrive via normal air conduction.

The brain then performs a fusion:

audio content personnel,
real sons of the environment.

This is the essence of "open-eared" listening:

music / calls / podcasts,
without disconnecting from the real world.

conclusion technique

A bone conduction headset is a complete system where:
digital signal → radio transmission → analog conversion → mechanical vibration → cochlea → auditory nerve → brain.

It is a solution designed for dynamic use: movement, safety, comfort, and maintaining environmental awareness.

ARTICLE 2 — SIMPLIFIED VERSION

From your phone… to your brain

Step 1: The sound originates in the phone

It all starts on your smartphone.

The music, podcast or call you are listening to is stored in digital form.
The phone transforms this data into a digital audio signal, then sends it wirelessly via Bluetooth.

👉 At this point, it is not yet sound, but simply coded information.

Step 2: Bluetooth transmission to the headphones

The bone conduction headset receives this Bluetooth signal.

The signal is decoded.
It is converted into an electrical signal.
then slightly amplified.

This signal is then sent to the transducers, the elements that will create the vibration.

Step 3: From electrical signal to vibration

This is where bone conduction makes all the difference.

Unlike a classic helmet:

No sound is sent into the air.
Nothing gets into the ear.

The electrical signal is transformed into micro-vibrations.

These vibrations are applied to a bony area of the face, most often:

the cheekbone,
or the area located just in front of the ear.

Step 4: Sound transmission through bone

Vibrations propagate naturally:

through the bones of the skull,
all the way to the inner ear.

👉The eardrum is not used.
👉The ears remain completely free.

The sound arrives directly at the cochlea, the organ that allows us to hear.

Step 5: Transformation into a nerve signal

Inside the cochlea:

Vibrations set the internal fluids in motion.
These movements are transformed into electrical signals.

It's exactly the same type of signal as during normal listening.

Step 6: The brain interprets the sound

These signals are sent to the brain via the auditory nerve.

The brain then takes care of:

to recognize the pitch of the sound (low or high),
determine the volume,
understanding speech, music and rhythm.

👉 For the brain, the sound is very real, regardless of the path taken.

Step 7: Listening + environment at the same time

Throughout the entire listening experience:

Your ears remain open.
You continue to hear the noises around you.

The brain naturally mixes:

the sound from the headphones,
and the threads of the environment.

This is what allows you to listen to music without cutting yourself off from the world.

Conclusion

Bone conduction is not a gimmick.

It is a reliable and well-established technology that transforms:
digital data → into vibrations → into nerve signals → into sound perceived by the brain.

A different way of listening, designed for:

the movement,
security,
and everyday uses.

How does it work? From the phone… to our brain