On amplifiers: how do they work and what are the different kinds? Premium

Learn how microphones and amplifiers work together to convert sound to electrical signals for clear audio output.

The amplifier remains a transformative invention for being able to receive the human voice and boost it so thousands of people can hear it at once. Without the microphone, politics itself may have evolved differently; the device has been ubiquitous in everything from public protests to political rallies. Amplifiers have also transformed entertainment, astronomy, search and rescue, medical diagnostics, and every human endeavour where some physical change can be converted to an electric signal. For simplicity’s sake, let’s focus here on audio signals.

A microphone is a type of transducer — a device that converts energy in one form to another, in this case from sound to electrical. There are different microphones for use in specific contexts, varying in terms of how they collect sound energy and how they convert it to electric signals.

Microphones in telephones and voice recorders are also called condenser microphones because they use capacitors to transduce audio signals (‘condenser’ is an old name for capacitors). A simple capacitor consists of two plates facing each other, separated in between by an air gap — or any suitable dielectric material — but connected on either side to a common circuit, including a power source. As the current enters one plate and builds up, it becomes depleted from the other. The difference creates an electric field between the plates that stores energy within the dielectric medium.

The ability of a capacitor to store energy is called its capacitance. A condenser microphone replaces one of the plates with a vibrating diaphragm. When a person speaks into the microphone, the diaphragm vibrates, altering the capacitance, which is converted to audio signals.

Once an audio signal is available, it is transported to a preamplifier (or preamp). Say there is an audio signal in the form of a varying voltage.

The preamp will acquire the voltage and supply it with more energy from an external power source while minimising noise. The ratio of the output of this process to the input is called the preamp’s gain.

The key to minimising noise is a step called impedance-matching. Impedance is a measure of how much a given circuit resists, or impedes, the flow of electric current (in a direct-current circuit, the impedance is equal to the resistance.)