How Do Wireless Headphones Work?

Modern technology is a true miracle. The past 100 years have brought an exponential explosion in technological innovation, jumpstarted by the Industrial Revolution. More advancements have been made in this time period than in the sum of the rest of all of human existence, which is both pretty astounding and also somewhat unsettling. In this article, we’ll break down a recent technological innovation that enabled us to make the jump from wired consumer headphones to wireless headphones. How do wireless headphones work, and who invented the wireless technology that enables them to function? Let’s take a deeper look.

Wireless Technology

In order to understand how wireless headphones work, we’re going to need to know a little bit about wireless communications and technology.

Wireless communication is simply the transmission of information between a transmitter and a receiver using electromagnetic radiation. It has history that dates all the way back to the 1880s. Most modern day wireless technology sends information using radio and microwaves.

Radio frequency (RF) waves and microwaves are a part of the electromagnetic spectrum, which encompasses all frequencies of electromagnetic radiation including visible light. RF and microwave radiation range from extremely low frequency (ELF) radio waves, which can have frequencies as low as 3 Hz, to extremely high frequency (EHF) microwaves, which can have frequencies up to a few hundred GHz.

Radio waves and microwaves encompass the relatively low-frequency regime of the electromagnetic spectrum.

Modulation

For wireless headphones to work, we need to use modulation. Modulation is a signal processing method which involves two types of waveforms:

• We call the first type the carrier wave. The carrier wave or carrier signal is usually a simple sinusoidal waveform.
• We call the second type the modulator wave. The modulator wave is the signal that modifies some property of the carrier wave, and is the wave that actually contains the information we want to transmit.

We call this entire modification process modulation. By modulating the carrier wave with the modulator wave, we can “encode” information into it and then transmit it through space at the speed of light.

There are many types of modulation. Each type describes what parameter or property of the carrier wave is modified by modulator wave. For instance, frequency modulation, also known as FM, is an analog modulation method where the frequency of the carrier wave is being modified by the modulator wave. This is how FM radio works. The radio frequency that you tune in to in your car is the frequency of the carrier wave in kHz.

We can see the analog modulation methods FM and AM in the animation above. The low frequency modulator signal is modifying the amplitude of the carrier signal in AM (amplitude modulation) and the frequency of the carrier signal in FM (frequency modulation).

Enter Bluetooth

Bluetooth is a wireless technology developed in the late 1980s as a means of connecting wireless headsets to mobile devices. Engineers at Ericsson Mobile first revealed their finished headset in 1999 at a tech conference. Throughout the early 2000s and 2010s, Bluetooth grew in popularity as one of the best wireless communication technologies for personal devices alongside WiFi.

Wireless Bluetooth Headphones

Armed with the basic knowledge of modulation and wireless technology we covered earlier, we can now attempt to understand how wireless headphones work. Bluetooth is the leading technology behind many modern wireless headphones and ear buds.

Bluetooth uses short-wavelength ultra-high-frequency (UHF) radio waves with carrier frequencies between 2.400 GHz and 2.485 GHz. It divides this range of frequencies into 79 separate frequency channels and chops up the signal into packets which get sent along the channels. Each packet get assigned a random channel at a rate of 1600 times per second in a process called frequency-hopping. The frequency channel randomization is synchronized between the paired devices to the enable transmission and reception of the packets in the right order. This also prevents two unpaired devices from communicating with each other.

We use Bluetooth to transmit digital signals between devices when streaming digital audio. Wireless headphones work by receiving a digital audio signal comprised of bits – the building blocks of computer language that are either a 0 or a 1. An MP3 file is nothing more than a series of 0s and 1s. The transmitter (your smartphone) sends a modulated waveform that contains this series of 0s and 1s to the receiver (your wireless headphones).

Phase-shift Keying

Bluetooth uses a type of digital modulation called phase-shift keying (PSK) to encode digital information (0s and 1s) into a sinusoidal electromagnetic carrier wave. In this type of modulation, the parameter being modulated is the carrier wave’s phase. Phase is simply the position of the waveform in it’s cycle, from 0 to 360 degrees.

With PSK modulation, each bit or set of bits in a serial stream of data symbolizes a phase shift in the carrier signal. For instance, in quadrature phase-shift keying (QPSK), every pair of bits in the digital serial data steam is encoded into the carrier wave as a phase change. 0 0 is a 315º phase angle, 0 1 is a 45º phase angle, 1 0 is a 225º phase angle, and 1 1 is a 135º phase angle.

Once the digital signal is encoded into the electromagnetic carrier wave, it can be transmitted through space to the receiver, your wireless headphones, allowing them to work and deliver you streaming audio.

Demodulation & Digital-to-Analog Conversion

Your wireless headphones contain the receiver which accepts the Bluetooth carrier signal from your smartphone. Then, the headphones demodulate the signal back into 0s and 1s. This is not the end of the story though. In order for your headphones to actually play audio and make sound, they need to be fed an analog signal. Digital bits of 0s and 1s are meaningless to analog devices like speakers and headphones.

To go from digital to analog, the signal must pass through a DAC, also known as a digital-to-analog converter. ADCs and DACs are found in many digital audio devices from audio interfaces to CD and DVD players. Once converted to analog, the signal drives the transducers of your headphones, producing the sounds your ears can understand, which is another fascinating process in itself.

Recap: How Do Wireless Headphones Work?

We covered a lot of complex information and theory here. Hopefully you don’t have a headache! Let’s do a quick recap on the subject.

• Electromagnetic radiation travels through space as a sinusoidal wave with a given frequency, amplitude, and phase.
• Wireless communication technology relies on the transmission and reception of electromagnetic radiation at varying frequencies.
• We can encode information into radio and microwaves using a process called modulation.
• Bluetooth uses modulated microwaves to encode and transmit digital information (0s and 1s) between two devices such as your wireless headphones and your smartphone.
• Bluetooth uses a digital modulation method called phase-shift keying. A change in the carrier wave’s phase symbolizes a change from a 0 to a 1 or vice versa when transmitting digital data
• Wireless headphones work by receiving the modulated carrier wave from your smartphone. They demodulate it into digital data (0s and 1s), and then convert the digital signal to an analog electrical waveform.
• The analog waveform gets fed to your headphone drivers to produce sound.

Thanks for reading, we hope you learned something interesting today. Any other questions? Let us know in the comments!