Sennheiser HMDC 27 Broadcast Headset, Dynamic Mic, Incl. NoiseGard

Sennheiser HMDC 27 Professional Circumaural Broadcast Headset

The Sennheiser HMDC 27 (Current Article Number: 700324, Legacy: 506978) is a premium, top-of-the-line closed-back circumaural (over-ear) broadcast headset engineered specifically for sports commentators, field journalists, and live audio engineers working in environments with extreme ambient noise levels (such as racetracks, football stadiums, or concert arenas).

The "C" designation sets this model apart within the 27-series family: it integrates Sennheiser's patented NoiseGard active noise cancellation (ANR) technology. This system combines high passive isolation with electronic noise reduction while utilizing a high-output dynamic microphone capsule to deliver broadcast-quality speech.

Key Acoustic and Operational Attributes

• Battery-Free NoiseGard Active Protection: The built-in Active Noise Cancellation (ANR) circuit suppresses an additional 15 dB of low-frequency rumble (such as engine roar, crowd drone, or PA build-up). It operates without batteries, drawing passive operating current directly from standard 12V to 48V phantom power on the incoming microphone channel.

• BMD 434 Dynamic Hypercardioid Microphone: Outfitted with a premium dynamic capsule that exhibits a highly directional hypercardioid polar pattern. It tracks vocals with high precision while ignoring ambient environment noise and preventing feedback from nearby public address systems.

• Onboard Switchable ActiveGard Limiter: Features an analog, mechanical switch-controlled ActiveGard circuit. When toggled on, it acts as an automatic safety buffer that tames unexpected incoming signal bursts over 110 dB SPL to shield the operator's hearing.

• Pressure-Free Two-Piece Split Headband: Uses an automatically opening split headband structure that spreads apart to shift pressure away from the sensitive areas of the skull. A wide, solid padding wrap is also included in the box for engineers who prefer a traditional single-band profile.

• Modular Multi-Pin Connection Base: Ships from the factory with an un-cabled connector socket. This modular design interfaces with Sennheiser's Cable-II series (such as the X3K1 XLR/1/4" combo cable), allowing technicians to replace damaged lines instantly or swap connection formats in the field.

Technical Specifications Matrix

In the Box: Production Package Inventory

• 1 x Sennheiser HMDC 27 Broadcast Headset

• 1 x Broad Single Headband Converting Cushion

• 1 x High-Density Wind and Pop Screen

• 1 x HZS 11 Cable Attachment Anchor Clip

• 1 x Quick Start Technical Guide

• (Note: Connection cables are sold separately according to studio infrastructure needs).

Field Configuration and Power Management Advice

Powering the NoiseGard Active System Safely: Because the internal NoiseGard circuit is engineered to be battery-free, it relies entirely on the P12 to P48 Phantom Power line sent down the microphone XLR path from your mixing console, intercom matrix, or commentator unit. If your incoming microphone channel strip's 48V phantom power toggle is turned off, the microphone will still work perfectly as a passive dynamic element, but the electronic active noise cancellation system in the ear cups will remain inactive. Turn phantom power on to activate the extra 15 dB of environment noise reduction.

Proper Strain Relief Integration: When threading your chosen single-sided Cable-II module into the headset cup harness, always line up the fine pins squarely before tightening the tiny structural anchor screw. Snap the cable into the included HZS 11 cable clip mounted to the headband frame. This configuration creates a physical strain-relief loop that prevents physical tugs on the cable from pulling on the internal pin matrix.