Microphone Types — Transducers, Polar Patterns, and AV Applications

Microphone selection is the most consequential audio decision in a conferencing or presentation system. A well-placed, appropriate microphone feeding a modest DSP outperforms an expensive DSP trying to rescue poorly placed or mismatched microphones. Understanding transducer types, polar patterns, and the acoustic environment they will operate in determines whether the system works from day one.

Transducer Types

Dynamic (moving coil) — A diaphragm attached to a voice coil moves within a magnetic field, generating voltage proportional to diaphragm motion. No power required. Robust and resistant to moisture, handling noise, and high SPL. Self-noise is higher than condenser; high-frequency transient response is slower. Used in handheld vocal mics (Shure SM58), instrument mics (SM57), and any application where durability or high-SPL handling is needed. Generally not ideal for conference room pickup where sensitivity and flat response matter more than durability.

Condenser (capacitive) — A thin diaphragm forms one plate of a capacitor; voltage across the capacitor changes as the diaphragm moves. Requires phantom power (48V DC via the mic cable, or battery). Condensers have lower self-noise, wider frequency response, and better high-frequency transient response than dynamics. Standard in conferencing, studio recording, broadcast, and speech reinforcement. All boundary mics, most ceiling mics, and all modern beamforming arrays use condenser elements.

Electret condenser — A condenser where the diaphragm or back plate holds a permanent electrical charge, eliminating the need for a polarizing voltage. Phantom power runs the internal preamp electronics only, not the capsule. Most small-diaphragm condenser microphones (lavaliers, boundary mics, small overhead condensers) are electrets. Performance is essentially indistinguishable from true condenser in most AV applications.

MEMS (Micro-Electro-Mechanical Systems) — Miniature silicon transducers used in modern beamforming array microphones (Shure MXA series, Biamp Parlé, Sennheiser TeamConnect Ceiling). MEMS capsules are extremely consistent in sensitivity and frequency response across mass production, enabling accurate beamforming with predictable inter-element matching.

Polar Patterns

The polar pattern describes from which directions a microphone is sensitive.

Omnidirectional — Equal sensitivity in all directions. Picks up from every angle simultaneously. Advantages: maximum bass response, no proximity effect (level does not change with distance), fewer room-to-room interaction issues. Disadvantage: cannot reject off-axis noise or adjacent talkers. Used in boundary mics placed on conference tables where all-around coverage from one position is needed, and in lavaliers where the mic is body-mounted.

Cardioid — Maximum sensitivity on-axis (front); reduced sensitivity at 90°; minimum sensitivity at rear (~180°). The most common pattern for handheld vocal mics. Front-to-back rejection ~20 dB. Useful in lecterns and podiums where on-axis placement is controlled and rear rejection helps feedback margin. Proximity effect (bass boost when mic is close to source) is a cardioid characteristic to manage in close-miking applications.

Supercardioid — Narrower front lobe than cardioid; ~12 dB side rejection; small rear lobe at 150° null. Better on-axis discrimination than cardioid; more directional. Common in theatrical overhead hanging mics and in conferencing systems where source-to-mic distance is fixed and angular discrimination is valuable.

Hypercardioid — Narrower still; rear lobe larger than supercardioid (~6 dB). Provides the highest front-to-side rejection but with an audible rear lobe. Used in high-gain applications (musical theater, broadcast) where maximum isolation is needed.

Bidirectional (figure-8) — Maximum sensitivity on both front and rear; minimum at sides (90°). Used in mid-side (M/S) stereo recording and in specific interview setups. Rarely used in AV conferencing; ribbon mics are typically figure-8.

Beam (steered) — Not a physical pattern but a computationally synthesized lobe created by a beamforming array. The array software combines signals from multiple capsules with calculated delays and gains to create a narrow, electronically steered pickup beam. Beam width adjusts with frequency; typical conference room beamformers maintain an 80-100° beam at conversational frequencies.

Key Microphone Specifications

Signal-to-noise ratio (SNR) in practice: A microphone with EIN of 18 dBA in a room at NC-40 (~47 dBA) has negative effective SNR — the room noise is louder than the mic's noise floor. This is why NC-30 is the maximum acceptable noise level for professional conferencing.

Microphone Types by AV Application

Beamforming Microphone Arrays

Beamforming arrays use multiple capsules combined via DSP to create electronically steerable pickup beams. Advantages over discrete mics:

• Invisibility — Ceiling-mount arrays (Shure MXA910, Biamp Parlé TEC, Sennheiser TeamConnect Ceiling 2) disappear into the architectural design. No table clutter.
• Full-room coverage — A single array covers an entire conference table or boardroom area, adapting automatically to talker position.
• Superior AEC complementarity — Beamforming attenuates the loudspeaker signal by 15-25 dB before AEC processing, dramatically improving echo cancellation performance.
• Spatial filtering — Beams null the loudspeaker direction automatically on many systems (Shure IntelliMix P300, Biamp TesiraFORTE), reducing the echo burden on AEC.

Key beamforming systems: Shure MXA910 (ceiling, steerable beams), MXA920 (wider coverage, adaptive coverage mode), Biamp Parlé TCM (ceiling, auto-coverage), Sennheiser TeamConnect Ceiling 2 (ceiling, adaptive coverage), ClearOne BMA360 (ceiling, 360° coverage), Nureva HDL300/HDL310 (wall-mount, full-room coverage via microphone mist technology).

Wireless Microphone Systems

Wireless microphone systems consist of a transmitter (handheld or bodypack with lavalier) and a receiver (rack-mount or standalone) connected to the DSP input.

UHF (470–698 MHz) — Traditional wireless range. Stable, long range (up to 300+ feet line-of-sight). Requires frequency coordination in multi-system environments; licensed spectrum in the US (FCC Part 74 for professional systems). The 600 MHz band (617–652 MHz) was sold to carriers in 2017 — equipment operating in this range is illegal in the US. Always verify equipment operates in the 470–608 MHz range.

DECT (1.9 GHz) — Digital European Cordless Technology. Used in professional conferencing wireless systems (Sennheiser SL Wireless, Revolabs). No frequency coordination required; license-exempt spectrum. Penetrates walls well. Maximum range shorter than UHF (100 feet typical). Interference from DECT phones possible.

2.4 GHz (Wi-Fi band) — Consumer wireless systems (Rode Wireless GO, some Shure systems). High interference risk in crowded AV environments with multiple Wi-Fi networks. Not recommended for professional installations.

Key receiver concepts: Diversity receivers use two antennas per channel in different positions, selecting the strongest signal moment-to-moment. Required for reliable wireless in reflective environments (glass walls, hard floors). Helical directional antennas and antenna distribution amplifiers extend range in large venues.

Frequency coordination — Multiple wireless systems must operate on non-interfering frequencies. Spectrum management tools (Sennheiser WSM, Shure Wireless Workbench) calculate intermodulation-free frequency assignments. For systems with 8+ wireless channels, formal coordination is essential.

Common Pitfalls

• Placing boundary mics near loudspeakers — Boundary mics have omnidirectional pickup and no inherent rejection of the loudspeaker. Placing them near speakers saturates the AEC reference with uncanceled echo. Place boundary mics at least 3 feet from any loudspeaker.
• Directional mics angled at ceiling reflections — Supercardioid and cardioid mics placed below-angle at ceiling-mounted speakers pick up ceiling reflections as if they were direct sound. Angle the mic at the talker, not the ceiling.
• Wireless in the 600 MHz band — UHF wireless gear manufactured before 2012 may operate in the 617–652 MHz band, which is now allocated to cellular carriers. This equipment is illegal to operate in the US and will experience interference. Check frequency range of all wireless gear.
• Lavalier under clothing — Clothing rubbing against a lavalier capsule creates low-frequency rumble. Use a foam windscreen; secure the cable to prevent movement; consider a chest harness mount rather than pocket clip.
• Mixing wireless and wired mic levels — Wireless receivers typically output line level (+4 dBu); some output -10 dBV consumer level. Match the input sensitivity of the DSP channel to the receiver output to avoid level mismatch artifacts.