AKG CM311 Headworn Condenser Microphone Four-Pin Locking Bodypack Plug

AKG CM311 With Four-Pin Termination: Upgrade the Microphone, Keep the Pack

The AKG CM311 in its four-pin configuration is a reference head-worn electret condenser microphone terminated in a four-pin miniature locking connector, the bodypack input fitted to many third-party wireless transmitters. It uses AKG Differoid noise-cancelling cardioid capsule geometry, covers 50 Hz to 17,000 Hz, delivers 1.25 mV/Pa sensitivity from a 6 kilohm unbalanced source into a recommended 10 kilohm load, and produces a 26 dB SPL A-weighted noise floor for a 68 dB signal-to-noise ratio at 94 dB SPL. The host pack supplies 3 to 9 V direct current at a nominal 0.27 mA, and maximum sound pressure runs from 140 dB SPL at 3 V to 148 dB SPL at 9 V. A carrying case, a WS-6 foam pop filter and a clothing clip are supplied. Its whole reason for existing is that a venue's transmitters and a venue's microphones do not have to come from the same order.

Four Pins Rather Than Three, and Why That Matters

Connector geometry is the only difference between the three CM311 configurations, and it is a genuine buying decision rather than a packaging detail. Four-pin miniature locking connectors became a widely used bodypack standard, so a great many wireless transmitters in service accept them, and a head-worn microphone fitted with that plug simply drops onto packs that a venue already owns; the sibling configurations terminate instead in a three-pin locking mini connector for AKG bodypacks or in a full-size balanced XLR for a wired console position. Adapters are not a satisfactory answer here, because a bodypack connector carries the bias voltage as well as the audio and the pin arrangement is what routes both correctly, so a mechanical adapter that fits may still deliver a signal at the wrong level or no bias at all. Establish which socket is on the packs that will actually be used, then order the matching configuration.

Keeping the Radios and Changing Only the Microphone

Retrofitting is what this configuration is for, and it addresses a very common situation: a venue whose transmitters work perfectly well but whose head-worn microphones have become worn, uncomfortable or acoustically inadequate. Radios have long service lives and are coordinated, catalogued and licensed into a room, whereas the microphone is the consumable part of the system, sitting in perspiration and being adjusted by different people every week, so replacing the microphone while retaining the packs is both the smaller intervention and the one that changes what the audience hears. Standardising the microphone across a mixed transmitter inventory has a second benefit, since every performer then wears the same thing and a monitor engineer stops chasing a different tonal balance on each channel. Rental houses, producing theatres, worship venues with accumulated equipment and corporate audio-visual departments all use this configuration for exactly that reason.

What the Host Pack Must Supply, and How to Check

Voltage is the compatibility question to settle before this microphone is fitted, since it needs 3 to 9 V direct current at the pack input and its maximum sound pressure depends on which end of that window the pack provides. A pack delivering around 3 V supports 140 dB SPL at 3 percent distortion, while one delivering 9 V supports 148 dB SPL, so eight decibels of clean headroom hangs on a specification printed in the transmitter's own documentation rather than on anything the microphone does. Electrically the microphone presents a 6 kilohm unbalanced source and wants a load of 10 kilohms or more, which is what a bodypack input is designed to offer, and current drain of 0.27 mA nominal is small enough that transmitter runtime is effectively unchanged. Reading the host pack's input specification takes a minute and settles the question, which is far quicker than diagnosing a channel that clips earlier than expected on a busy stage.

Headband, Boom and the Foam Pop Filter

Wearing comfort decides whether a head-worn microphone is used or quietly left in a drawer, and this one uses an adjustable headband of 5.5 in (140 mm) diameter with a boom measuring approximately 7 in (178 mm) by 3 in (76 mm). Adjustment range matters because a band that grips too hard becomes unbearable across a two-hour performance while a loose one slides and changes the working distance, which changes the level arriving at the capsule and therefore the mix; a boom of this geometry places the element at the corner of the mouth without crossing the front of the face where a camera would find it. Supplied alongside the microphone are a carrying case, a WS-6 foam pop filter that intercepts the breath blast on plosive consonants, and a clothing clip that anchors the cable so its weight never pulls on the headband. An internal shock mount inside the capsule housing handles the remaining mechanical problem, keeping headband and cable movement from arriving as low-frequency thumps.

Ambient Rejection and Who Standardises on This Configuration

Rejection of the room rather than reproduction of it is the acoustic argument for the CM311, and the Differoid cardioid capsule geometry is how AKG achieves it. A cardioid response is least sensitive directly behind the capsule, and the Differoid arrangement is designed to cancel ambient sound arriving from that direction while leaving the close voice untouched, which combined with a working distance of an inch or two means the wearer's voice arrives vastly louder than anything the loudspeakers are producing. That ratio is what a monitor engineer converts into usable level, and it is why head-worn microphones are the default on stages that fight for gain. Rental houses whose transmitter stock uses four-pin inputs, producing theatres standardising one microphone across mixed radios, touring productions carrying microphones but hiring local wireless, fitness studios with installed packs and conference venues that let performers supply their own head-worn microphone all order this configuration deliberately.