A cheap electret condenser element plus a bias resistor and blocking capacitor makes a studio-quality air microphone

Electret condenser microphone elements — the same capsules inside answering machines and studio mics costing hundreds of dollars — cost about US$2 and need only a handful of parts to work. The element requires a DC bias: a 9V battery feeds it through a series resistor, and a capacitor in series with the output blocks that DC voltage from reaching the amplifier or mixer. A switch conserves the battery, which drains very slowly. Three-wire elements are easier: separate signal, power, and shared shield/ground wires. When choosing an element, prefer high signal-to-noise ratio and flat, extended response; omnidirectional capsules are usually flatter than cardioid. These elements have extended bass (down to ~20Hz), so they capture subsonic pressure waves but are prone to wind and breath pops, often needing a bass roll-off.

Examples

Wire a 2-wire electret: 9V+ through a resistor to the element’s hot lead, hot lead also to a capacitor to the plug tip; element ground and battery- to the sleeve/shield. Two elements on headphones make a binaural rig; one at a parabolic dish focus makes a wildlife shotgun mic.

Assessment

Explain the role of the series resistor and the blocking capacitor in an electret mic circuit. Then predict what a performer would adjust to reduce breath-pop overload when recording close-up vocals.