Shotgun Microphone Product

Overview

The shotgun microphone is a highly directional condenser pickup used in broadcast, film, and video production to capture sound from a single source while rejecting room reflections and ambient noise. Its distinctive supercardioid-to-hypercardioid polar pattern results from an Interference Tube—a slotted acoustic resonator that makes rear and side sounds interfere destructively while on-axis sound reaches the Cardioid Condenser Capsule constructively. The result is a pickup that narrows as frequency rises, delivering clean dialogue recording and focused environmental sound in noisy settings.

How it Works

Interference Tube Design

The Interference Tube contains a series of precision-drilled Slotted Baffle Plate arranged axially along a 25 cm tube. Sound entering the Front Endcap mesh travels straight to the capsule; simultaneously, off-axis sound waves enter the slots and travel through internal passages at different path lengths. The slot spacing is tuned so that off-axis sound arriving at the rear of the capsule is 180° out of phase with the direct sound, causing cancellation. This geometric phase-shifting is frequency-dependent: lower frequencies are less efficiently rejected (cancellation requires slots spaced at wavelength intervals), while higher frequencies above 2 kHz exhibit near-total off-axis suppression.

Cardioid Capsule

The Cardioid Condenser Capsule is a back-electret design—a Diaphragm coated with a permanently charged polymer layer that maintains a constant electrical field between itself and the Backplate. When sound vibrates the diaphragm, the capacitance between diaphragm and backplate changes, modulating a DC bias voltage supplied by the Phantom Power Circuit phantom power network. The resulting signal is a low-level AC voltage (microvolts) mirroring the original pressure wave.

Directionality

The Acoustic Vent Port at the capsule rear allows sound to reach the back of the diaphragm, creating a passive cardioid response. The interference tube extends this directionality: its slots create a lobing pattern that narrows with frequency. At 1 kHz, the microphone exhibits supercardioid rejection (>25 dB attenuation at 180°); at 4 kHz, it approaches hypercardioid (near-zero pickup directly behind the microphone).

Preamplifier

The Preamplifier Module houses a low-noise Input Transformer matching the capsule's high impedance (>1 MΩ) to a buffer amplifier, and a Line Driver IC IC delivering a balanced, low-impedance XLR output at line level (−35 dBV nominal becomes +4 dBu at the connector). The preamp also extracts phantom power from the XLR cable's pins 2 and 3 via a Bias Resistor Array, applying that 48 V to the capsule backplate and internal biasing networks.

Shock Isolation

The Shock Mount and Bracket surrounds the microphone with elastomer rings that absorb vibration from camera rigs, tripods, and handling. The mount includes a Ball Joint Swivel permitting rapid angle adjustment without detaching the microphone from the camera or boompole.

Wind Rejection

The Windscreen Sleeve is a 2 cm layer of open-cell polyurethane foam. Wind flowing across the microphone creates pressure fluctuations; the foam's cell structure disrupts coherent airflow, converting kinetic energy into heat. The Foam Mesh Cover breathable nylon mesh retains the foam while allowing normal sound passage. Windscreens reduce wind rumble by 10–15 dB, critical for outdoor recording.

Polar Pattern and Frequency

Shotgun microphones exhibit frequency-dependent directionality. At low frequencies (250 Hz), the pattern approximates cardioid; at mid frequencies (1 kHz), it tightens to supercardioid; at high frequencies (4 kHz and above), it approaches hypercardioid with a sharp null at 180°. This means off-axis dialogue is progressively attenuated at higher frequencies, reducing room reflections while maintaining bass reverb presence.

Mounting and Operator Techniques

In film and broadcast, shotgun microphones are mounted on boompoles held by recordists positioned just outside the frame, angling the Shock Mount and Bracket to point at the talent. The interference tube must be aimed within approximately 30° of the sound source's axial direction for optimal rejection. Rotating the microphone by 90° degrades directional performance. The cable is typically routed through a microphone cable with low-impedance, oxygen-free copper twisted pair to minimize RF ingress and maintain signal fidelity.

Comparison with Omnidirectional Microphones

Omnidirectional microphones pick up equally from all directions and rely on close placement (within 30 cm) to preserve the direct-to-ambient ratio. Shotgun microphones permit placement further away (0.5–2 meters) while maintaining high direct-sound pickup and off-axis rejection. This distance permits boompoles to remain outside camera framing during cinema production and offers safe stand-off distance from wildlife in nature recording.

Maintenance

The Windscreen Sleeve should be washed in lukewarm soapy water and air-dried regularly; compressed air can temporarily restore foam compliance. The Aluminum Tube interior should be inspected for dust; if necessary, a soft brush or compressed air removes debris without disturbing the slotted baffles. XLR connectors should be stored with protective caps and exercised periodically (mated and unmated) to prevent corrosion.