The condenser microphone and its electret variant dominate modern microphone technology

Evidence

Many conversion principles have been applied in microphones, but many of them, for example the carbon microphones used earlier in telephones, have become obsolete. The most important technology nowadays is the condenser microphone and its variants. Figure 4.2 illustrates the basic physical principle and a typical construction principle of a high-quality condenser microphone used for acoustic measurements and research purposes. The sound pressure variations in the air make one electrode of the condenser move while the other is kept fixed. If an electric charge is present between the electrodes, a change in distance between the electrodes will change the voltage between the electrodes. When this weak voltage signal is amplified inside the same microphone unit, the signal can be fed through a cable to audio equipment over reasonable distances. In the construction of Figure 4.2, the electric charge on the electrodes is provided from an external voltage source. A variant of the condenser microphone, the electret microphone, is based on using an electret material, which has electric charge trapped within, between the electrodes so that no external voltage is needed. A built-in amplifier is required here as well. Electret microphones have found widespread use especially in portable devices. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 482

Categorization

• DEFINE: Explains the physical operating principle distinguishing condenser microphones (external voltage charge) from electret microphones (trapped charge).
• CANDY: Nice elevator fact: your phone’s mic works because electricity is permanently trapped inside a material, needing no battery for the sensing element itself.