Speaker / Microphone
Transducer
Transducers between electricity and sound. A speaker turns current through a coil-in-magnet into cone motion; a dynamic microphone is literally the same thing run backwards. Impedance and power matching make or break them.
Schematic symbol
Loudspeaker
How speaker / microphone appears in a circuit diagram.
Types & variants
Key specs
Impedance
Ω4 or 8 Ω speakers; amplifier must be rated for it.
Power handling
WRMS rating — exceeding it burns the voice coil.
Sensitivity
dB/W/mLoudness per watt; 3 dB more = half the power needed.
Frequency response
HzSmall speakers roll off sharply below a few hundred Hz.
Markings
Impedance and wattage stamped on the magnet (e.g. 8Ω 0.5W). Electret capsules: the pin tied to the case is ground.
Standard values
8 Ω 0.5 W mini speakers, 5 V active buzzers, 9.7 mm electret capsules.
How to choose
Match impedance to the amp and don't starve power. Passive buzzer if you want tunes (you supply the tone), active if you just need a beep. MEMS mic (I2S) skips the analog preamp entirely.
Pinout & package
Speakers: 2 terminals, + marked for polarity consistency between multiple drivers. Electret: 2 pads, polarity matters, needs bias resistor.
Example circuits
- PAM8403 amp module driving an 8 Ω speaker
- Passive buzzer playing melodies from a PWM pin
- MAX9814 electret preamp into an ADC
Common failures
Torn cones and burnt voice coils (over-power), buzzers driven with the wrong type (active fed PWM sounds awful; passive fed DC is silent), electret capsules dead from missing bias.
How to test
Resistance across a speaker ≈ its impedance (8 Ω reads ~6–7 Ω) with a faint click as probes touch. Open = dead coil. Electret mic: needs the bias resistor before you'll see any signal.
Substitutes
Any speaker of same impedance and ≥ power rating; piezo disc for beeper duty; MEMS I2S mic in place of electret + preamp on modern MCU builds.