Traditional headphones depend on a thin, flexible electronic cable, which carries a signal from a music player to the earphones. The wires in this cable get stressed every time the cable is moved or bent. Over time, this can add static, degrade sound quality and even cause the headphones to fail. Infrared headphones solve this problem by substituting wireless technology for audio cables. Their greater durability and convenience make them a popular use for portable travel systems and home audio systems alike.
Transmitting the Signal
The music player sends the sound as an electronic signal to an infrared transmitter. The transmitter digitally encodes the sound, turning it into a sequence of electrical pulses. The pulses are sent to a special light called an infrared LED or light-emitting diode. The LED flashes on and off very rapidly with the pulsing signal.
Pulses of Light
An LED is an efficient, low-power light which can be turned on and off very quickly. An infrared LED produces a specific wavelength of infrared light. Infrared lies right below the visual spectrum, meaning that it can not be seen by human eyes. In most ways, however, it is identical to visible light. Like visible light, infrared can bounce off objects, be absorbed or reflected by different materials and be blocked by an obstacle. Therefore, anything receiving the infrared signal has to either be within line-of-site or near something that bounces the signal off. The infrared receiver also has to be pretty close to the transmitter, or else the signal is too faint to detect.
Receiving and Playing the Signal
The headphones are attached to a small receiver with a light detector called a CdS cell. The CdS cell in the headphones is designed to only react to the frequency of infrared light broadcast by the transmitter. When light shines on the cell, the cell produces a pulse of electricity. The receiver turns the pulses of electricity back into the original sound signal, then sends them to the headphones for the user to listen to.