Explained
How a wireless earbuds works.
How wireless earbuds work
Wireless earbuds look simple from the outside, but each one is a complete audio system. Inside the shell there is a speaker driver, a rechargeable battery, several microphones, a Bluetooth radio and a small computer that ties them together. Your phone sends compressed audio over Bluetooth. The earbud's chip decodes it, applies any equalisation or noise cancelling, and drives the speaker.
The speaker, called a driver, works like a full-size loudspeaker. A coil of very fine wire is attached to a thin diaphragm and sits in the field of a small permanent magnet. When the audio signal flows through the coil it becomes an electromagnet, pushed and pulled by the fixed magnet, so the diaphragm moves back and forth and pushes the air in your ear canal. The silicone tip seals the canal, which is why a good fit sounds so much fuller in the bass.
Noise cancelling and microphones
Active noise cancelling uses microphones on the outside of the bud to listen to the sound around you. The processor creates a copy of that sound that is inverted, so its peaks line up with the troughs of the original. When both reach your ear they cancel each other out through destructive interference. A second microphone inside the bud checks what is left and corrects the result. It works best on steady, low sounds like engine hum.
The same microphones handle calls. They are spaced apart so the processor can compare their signals and focus on sound coming from your mouth. Transparency mode does the opposite of noise cancelling, feeding outside sound through so you can hear traffic or a conversation.
Battery, radio and the case
The battery in each bud is tiny, usually a lithium-ion cell holding only a small fraction of the energy in a phone battery, so efficiency matters everywhere. The antenna sits in the stem, away from your head, because the body absorbs 2.4 GHz radio waves. The technology is named after a 10th-century Danish king, Harald Bluetooth, who united tribes, much as the standard was meant to unite devices.
The charging case is really a power bank. Magnets pull each bud into place so two metal contacts on the stem touch spring-loaded pins, and the case's larger battery tops the buds up. This model is a generic illustration, not any particular brand. Use Explode to separate the parts, or open Play to remove each layer in turn.
Parts glossary
- Silicone ear tip
- The soft tip seals the ear canal. A good seal blocks outside sound passively and lets the driver deliver deep bass with very little power.
- Shell
- The moulded plastic shell holds everything in place and is shaped to sit in the bowl of the ear. Here it is shown translucent so you can see inside.
- Speaker driver
- A tiny diaphragm, a voice coil and a magnet make up the driver. Current through the coil pushes the diaphragm back and forth, moving air to make sound. Fun fact: A typical earbud driver is around 6 to 12 millimetres across.
- Microphones
- Outward-facing mics hear the world for noise cancelling and transparency, while others pick up your voice for calls. Fun fact: Noise cancelling plays an inverted copy of outside sound, so the two waves cancel out by destructive interference.
- Logic board
- A small board carries the Bluetooth chip, audio processor and power management. It decodes the music and runs noise cancelling many thousands of times a second.
- Battery
- A small lithium-ion cell, often a button-shaped coin cell, stores the energy for a few hours of listening.
- Antenna
- The stem houses the antenna, placed away from your head so the 2.4 GHz Bluetooth signal reaches your phone. Fun fact: Bluetooth uses the 2.4 GHz radio band, the same one used by Wi-Fi and microwave ovens.
- Ear-detection sensors
- Optical or capacitive sensors notice when the bud is in your ear, so music can pause when you take it out.
- Charging contacts
- Two metal pads at the tip of the stem touch spring pins in the case. That is how the bud charges without a socket.
- Charging case
- The case is a portable battery with a magnetic lid. It refills the buds several times and holds them in exactly the right spot.
