Wireless Headphones Use a "Base Unit"
Although the most visible portion of the wireless headphone may be several feet away from the audio receiver, some portion of the headphones must physically connect to the receiver to get sound signals. The portion that connects to the audio receiver is known as a base unit, and may be internal to the receiver or connected by way of speaker wire or audio cable. The receiver sends sound to the wireless headphones base unit in the form of electrical impulses, which must travel over these physical wires as a medium before being prepped for transmission through the air.
The Base Unit Sends Radio Signals
When the wireless headphones base unit receives electrical impulses from the audio receiver, a processor in the base unit begins converting the impulses into radio waves. Since most wireless headphones work on a frequency modulation (FM) channel, the radio waves generated by the base unit must fall within a very narrow band of frequencies. Slight alterations in the frequency--as little as 5 Hz--carry the actual sound content over the air and to the headphones. Depending on the brand and capabilities of the wireless headphones, the base unit may contain a built-in antenna from which the radio waves are broadcast, or it may use a feed to an external antenna that is mounted in the home, in the office or even outside for broadcasting over greater distances.
Headphones Convert Radio Waves Back Into Sound
The headphone portion of wireless headphones actually features two separate parts: a radio receiver and at least one speaker. The radio receiver catches passing radio waves through either a built-in or a protruding antenna. As the radio waves pass by, they excite electrons within the antenna and create an electric signal. The electric signal is fed to a small processor where noise, static and out-of-frequency interference is stripped out, then the clean signal is passed to the speakers. As the speakers within the wireless headphones receive the electric signals, they use electromagnets to create a physical vibration on the speaker membrane. This vibration is transferred through the air--and received by the listener--as audible sound.