The base unit, or transmitter, connects to a sound-generating piece of equipment, such as a TV, receiver or surround system. This transmitter converts sound impulses into one of three main transmission types currently used--radio frequency (RF), infrared (IR) or the more recent Bluetooth, which is a kind of radio wave, as well.
The range of each differs--with radio being the most versatile and best suited to mobile listening. Infrared tends to have a short range, typically under 30 feet, because of wave dispersion and lower penetration of barriers such as walls and furniture.
A receiver that is actually on the headphones takes the transmission and converts it into sound, as per normal headphones, except the compression ratio is different. The amplification process is identical to corded, or wired, sets. Most headphones have an autonomous speaker for each ear. However, unlike wired models, wireless headphones rely on an immediately finite power source--batteries. This is because they are not passive, as are wired headphones, and call for a power source to drive their sound engines and amplifiers. Wired sets get their power directly from the driving device.
The transmitter also needs a power source in most cases--but can be easily connected to a wall outlet. Some models have amplifiers that can get power from the driving device, but these tend to be low impedance, shorter range sets.
Wireless headphones rarely have impedance over 64 ohms because it has been shown amplification at higher levels drains batteries to the point of impracticality. Many now use rechargeable NiMH batteries that power up very quickly.
Compression plays a more important role in wireless headphones than in their normal counterparts--due to sound dissipation into the environment and the lack of insulated wire conduction, wireless models rely on more powerful compression. As a result, they cost more compared to similarly performing wired units.
Tags: driving device, from driving, from driving device, power source, that power
