A microphone turns sound energy into an electrical signal that can be recorded, amplified, or analyzed. Sound begins as pressure variations in air, such as the compressions and rarefactions created by a singer, guitar, or speaker. When these waves reach a microphone, they make a small internal part move back and forth.
This conversion matters because nearly all recorded music, podcasts, phone calls, and live performances depend on accurate sound capture.
In a dynamic microphone, incoming sound waves vibrate a thin diaphragm attached to a coil of wire. The coil moves inside a magnetic field, which induces a changing voltage that matches the pattern of the sound wave. Louder sounds create larger diaphragm motion and stronger electrical signals, while higher-pitched sounds make the diaphragm move more times per second.
The microphone signal can then be sent through a cable to a mixer, amplifier, computer interface, or recording device.
Key Facts
- Sound is a longitudinal pressure wave made of compressions and rarefactions in a medium such as air.
- Frequency determines pitch and is measured in hertz: f = 1/T.
- Wavelength, frequency, and wave speed are related by v = fλ.
- In air at room temperature, sound travels at about v = 343 m/s.
- A dynamic microphone uses electromagnetic induction: moving coil + magnetic field produces voltage.
- Louder sound usually means greater pressure amplitude, which causes larger diaphragm motion and a larger output signal.
Vocabulary
- Diaphragm
- A thin flexible surface inside a microphone that vibrates when sound waves strike it.
- Dynamic microphone
- A microphone that produces an electrical signal by moving a coil of wire in a magnetic field.
- Electromagnetic induction
- The production of voltage when a conductor moves through a magnetic field or experiences a changing magnetic field.
- Frequency
- The number of wave cycles that pass a point each second, measured in hertz.
- Amplitude
- The size of a wave's variation from its resting value, related to loudness for sound waves.
Common Mistakes to Avoid
- Confusing pitch with loudness is wrong because pitch depends mainly on frequency, while loudness depends mainly on amplitude and sound intensity.
- Thinking a microphone records sound waves directly is wrong because it converts air pressure vibrations into an electrical voltage signal.
- Assuming all microphones work the same way is wrong because dynamic, condenser, ribbon, and piezoelectric microphones use different physical mechanisms.
- Ignoring distance from the sound source is wrong because sound level decreases with distance and the microphone receives a weaker pressure variation.
Practice Questions
- 1 A singer produces a note with frequency 440 Hz. Using v = 343 m/s, calculate the wavelength of the sound in air.
- 2 A sound wave has a period of 0.0025 s. Calculate its frequency and state whether it is likely to sound low, medium, or high in pitch compared with a 100 Hz tone.
- 3 Explain why a louder drum hit produces a larger microphone signal even if the pitch of the drum sound does not change much.