A headset microphone is a small, very lightweight electret microphone attached to a headband that can be adjusted to allow the microphone to pick up speech near the mouth.
The headband is made of elastic, often transparent material, and is often adjustable in length and rotatable in the capsule arm. This allows the electret or condenser microphone, which is located at the end of the headband, to be optimally aligned for speech recording. The microphone capsule of the headset microphone is characterized by the highest sound quality and has a cardioid or omnidirectional characteristic that tolerates certain alignment deviations.
The bandwidth of the electret capsule covers the entire audible frequency range from 20 Hz to 20 kHz. Microphone impedances range from 500 ohms to 1.5 kilo-ohms, and those at a few millivolts (mV) relative to sound power at 1 kHz.