Microphone Types, Sensitivity, and Performance Characteristics

Microphone Fundamentals

A microphone (MIC) is an element that captures sound waves, converting pressure variations into electrical energy. This process involves a diaphragm with specific properties, followed by electronic signal processing.

Transducers

A transducer is a device activated by received energy, transforming it into another energy type. Microphones utilize transducers, including:

• Mechanical-acoustic transducer
• Transducer-mechanical
• Electrical transducer

Microphone Classification

By Acoustic Mechanism

• Pressure Microphone (Omnidirectional): Equal sensitivity in all directions.
• Gradient Microphone (Bidirectional): Sensitive to sound from front and rear, attenuating sounds from other directions.
• Combination Pressure and Gradient Microphones:
  • Unidirectional: Captures sound primarily from the front.
  • Hypercardioid: Small rear lobe, response between bidirectional and unidirectional.
• Interference (Shotgun) Microphone: Captures specific sounds, eliminating others.

By Electrical Transducer Type

• Variable Resistance (Carbon Microphone)
• Piezoelectric Microphone
• Moving Coil (Dynamic) Microphone
• Ribbon Microphone
• Electrostatic Condenser Microphone (Electret)

Microphone Performance Characteristics

Sensitivity

Sensitivity is the relationship between the sound pressure level (SPL) acting on the diaphragm and the resulting electrical output voltage at 1 kHz. Sensitivity Level is expressed in decibels (dB) relative to a reference sensitivity.

Frequency Response

Frequency response describes how microphone sensitivity varies across the audible frequency spectrum and with the angle of incidence.

Directivity

Directivity indicates the microphone's output level for different angles of sound incidence.

• Omnidirectional: Picks up sound equally from all directions.
• Bidirectional: Receives sound from front and back.
• Unidirectional: Primarily captures sound from the front.
• Hypercardioid: Enhanced directionality with a small rear lobe.

Impedance

Internal impedance is the resistance to alternating current flow. Microphones can have high or low impedance.

Dynamic Range

Dynamic range is the difference between the loudest and weakest sound levels a microphone can reproduce without distortion.

Distortion

Distortion refers to unwanted signals in the output that were not present in the input.

Linearity

Linearity is the microphone's ability to provide an output voltage proportional to the pressure exerted on its diaphragm.

Microphone Operating Principles

Variable Resistance (Carbon) Microphone

Operation relies on changes in pressure causing variations in the resistance of carbon granules.

Piezoelectric Microphone

A piezoelectric element generates an electric charge when deformed by sound waves.

Moving Coil (Dynamic) Microphone

A coil moves within a magnetic field, generating an electrical signal due to the force from sound waves.

Electrostatic Microphone

Operation is based on changes in capacitance between capacitor plates.