A microphone’s sensing principle determines whether its pickup pattern is omnidirectional, dipolar, or cardioid

Evidence

A directional pattern is an important property in microphones. The basic structure of Figure 4.2b is a pressure microphone that has an omnidirectional pattern, which means it is equally sensitive in all directions. If a microphone is sensitive to the particle velocity in air, the directional pattern is a dipole that reacts at the main axis from front and back but not from the sides. A cardioid microphone, which is a useful compromise, is maximally sensitive from the front and minimally sensitive from the rear. It is also possible to construct highly directional microphones that are sensitive only to sound coming from a narrow spatial angle. Microphone arrays together with signal processing can be used to make systems where the directional pattern of the resulting signal is controllable electronically. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 487

Categorization

• DEFINE: Clearly connects physical sensitivity (pressure vs particle velocity) to resulting directional patterns: omnidirectional, dipole, and cardioid.
• QUESTION: Worth chasing: exactly how do microphone arrays make directional patterns electronically controllable, and what mathematics underlies beamforming?