What Are Microphone Polar Patterns in Live Sound?
Microphone polar patterns dictate how a capsule captures sound arriving from different angles, serving as the foundational tool for managing bleed, phase coherence, and acoustic feedback in live sound environments. Understanding the directional sensitivity, null points, and frequency-dependent behavior of patterns such as cardioid, supercardioid, hypercardioid, omnidirectional, and bidirectional allows audio engineers to isolate target instruments while rejecting high-decibel stage noise. This guide breaks down the core physical principles governing polar patterns, their direct impact on stage monitor placement, and practical strategies for capturing clean live instrument signals.
The Physical Mechanics of Directional Response
A microphone’s polar pattern represents its sensitivity plotted on a 360-degree, two-dimensional polar graph relative to its central axis (0 degrees). Directional characteristics are engineered using acoustic resistance and phase-delay networks behind the diaphragm:
- Pressure Transducers (Omnidirectional): The diaphragm is open only to the front, measuring absolute changes in air pressure regardless of arrival direction.
- Pressure-Gradient Transducers (Directional / Bidirectional): Both sides of the diaphragm are exposed to sound waves. Directionality is achieved through phase cancellation caused by the time-delay path between the front and rear ports.
Because sound wavelengths vary drastically across the audible spectrum, polar patterns are inherently frequency-dependent. A directional microphone typically behaves more omnidirectionally at sub-bass frequencies and becomes increasingly narrow and laser-focused at high frequencies.
Core Polar Patterns Used in Live Production
Selecting the correct pattern requires balancing front acceptance angle against rear and side sound rejection.
1. Cardioid (Unidirectional)
The standard cardioid pattern provides maximum sensitivity at 0 degrees and maximum rejection (null point) directly behind the capsule at 180 degrees. Its broad front acceptance angle (roughly 130 degrees) allows performers slight movement off-axis without dramatic tonal variation, while effectively rejecting sound directly behind the microphone.
2. Supercardioid and Hypercardioid
These tighter directional patterns narrow the front pickup angle (approximately 115 degrees for supercardioid and 105 degrees for hypercardioid) while providing greater isolation from side sound sources. However, they introduce a small rear pickup lobe.
- Supercardioid null points: Located at approximately 126 degrees off-axis on either side.
- Hypercardioid null points: Located at approximately 110 degrees off-axis on either side.
3. Omnidirectional
Omnidirectional capsules respond equally to sound arriving from all angles (360 degrees). While rarely used for close-miking loud sources on high-gain stages due to feedback vulnerability, omni capsules possess zero proximity effect and lower handling noise, making them useful for specialized acoustic instruments, lavaliers, and measurement tasks.
4. Figure-8 (Bidirectional)
A figure-8 pattern captures sound equally from the front (0 degrees) and rear (180 degrees) with complete 90-degree side null planes. In live settings, these sharp side nulls allow engineers to aim dead zones directly at adjacent loud sources, such as positioning a snare-side null directly toward a hi-hat.
Essential Principles for Stage Optimization
Deploying polar patterns effectively on a live stage involves three primary acoustic considerations:
Aligning Monitor Nulls to Prevent Feedback
Gain-before-feedback depends on aiming the microphone's null point directly at the primary source of amplified stage sound, usually the floor monitor.
- Cardioid mics: Place a single floor wedge directly in front of the performer, aimed at the microphone’s 180-degree rear null.
- Supercardioid/Hypercardioid mics: Place dual floor wedges split to the sides (at 120–130 degrees or 110 degrees off-axis) to align with the dual side-rear nulls, avoiding the sensitive rear lobe.
Managing Acoustic Bleed and Phase Relationships
Stage spill cannot be eliminated entirely, but its tonal impact can be controlled. When bleed enters an off-axis pattern, uneven off-axis frequency response can color the spill with an unnatural, hollow tone. Matching polar responses across multi-mic setups—such as drum kits—minimizes phase cancellation when adjacent microphones capture overlapping sources.
Controlling the Proximity Effect
All pressure-gradient (directional) microphones exhibit the proximity effect: an increase in low-frequency response as the sound source moves closer to the capsule.
- Hypercardioid and supercardioid capsules produce the strongest proximity effect, requiring high-pass filtering or careful distance management on sources with heavy low-end energy.
- Cardioid capsules produce moderate proximity effect, providing useful low-end reinforcement on instruments like kick drums, toms, and electric guitar cabs when placed within a few inches.
- Omnidirectional capsules exhibit no proximity effect, maintaining consistent frequency response regardless of working distance.
Instrument Miking Applications
Applying these principles to specific instruments ensures high isolation and consistent mix translation:
- Drum Kit Close-Miking: Hypercardioid dynamic microphones isolate rack and floor toms by keeping cymbal bleed inside the side nulls. Snare top microphones benefit from tight cardioid or supercardioid patterns with the rear null aimed at the hi-hat.
- Guitar Amplifiers: Cardioid dynamic capsules placed close to the speaker grille reject spill from drums and bass while utilizing proximity effect to capture low-mid punch.
- Acoustic Instruments: On quieter stages, supercardioid small-diaphragm condensers offer isolation for acoustic guitars and violins. When bleed from adjacent wedges is severe, clip-on directional miniature capsules positioned close to the soundboard yield the highest usable gain.