Electro-Voice CO2
A 36-gram back-electret lavalier with a broadcast-grade condenser inside a paintable black shell.
Overview
The CO2's electronics module is 93 mm long and 19 mm in diameter. The whole microphone, capsule and attached cable included, weighs 36 grams. It's light enough that the supplied tie bars and clips do the work of holding it in place. Electro-Voice built it as an omnidirectional back-electret condenser lavalier. The manual is plain about the tradeoff in that polar pattern: the mic is intended for broadcast and sound reinforcement work where acoustic feedback problems are minimal. An omni lav picks up evenly from every direction. That suits a moving performer and does badly in a loud, live, feedback-prone room. The company's own documentation says so and doesn't pretend the CO2 is a stage mic.
The capsule is brass, just 5.3 mm across, and it's permanently tied to the electronics housing by 2.6 meters of miniature two-conductor shielded cable. The literature calls the cable high-strength and flexible, built for professional use. Lavs get clipped to lapels, yanked, coiled and stuffed in pouches, so the fixed cable is both the CO2's durability story and its likely failure point. There's no connector to swap, so when the cable goes, the mic goes. The electronics module is polycarbonate resin wrapped in insulated copper foil for EMI/RFI rejection, which helps when the mic sits near a transmitter or a lighting rig.
Frequency response is 50 Hz to 20,000 Hz, full-range and, in the manual's words, well-balanced. Sensitivity is 8.5 mV/pascal at 1 kHz, with a power level of -38 dB referenced to 1 mW/pascal. Output impedance is 100 ohms nominal, balanced, and a positive pressure on the diaphragm produces positive voltage on pin 2. That's standard, so it works with any correctly wired console. It runs on 12 to 52 volts of phantom power and draws 1.0 mA, so nearly any phantom supply will feed it. Dynamic range is quoted at 128 dB, with equivalent noise below 29 dB SPL A-weighted typical. That's a quiet, wide-range front end for a lav this small, and it explains why the CO2 turns up in broadcast bags and not only in conference rooms.
The surface is the odd feature. Electro-Voice called it Tincture, and it accepts acrylic lacquer paint, so the mic can be blended into whatever it's clipped to. A black lav looks fine until it lands on a white shirt or a costume. The CO2 shipped in nonreflecting black (CO2, CO2Pro) or white (CO2-W, CO2Pro-W). The standard CO2 came with single and double mic tie bars, a single cable-holding tie bar, and a zippered vinyl pouch. The CO2Pro added a mic tie tack, a cable tie tack, a mic vampire clip, and a cable vampire clip. Those are more ways to mount it out of sight.
First, what the documentation establishes and what it doesn't. The manual is the source for everything above. It gives no production years, no original price, and no independent review data. The period-review chunks in the archive don't contain a CO2 review. The EQ Magazine (June 1996, p.91) chunk is an unrelated UHF radiomicrophone listing, and the Audio (December 1967, p.3) chunk is a masthead page. Neither mentions this microphone. So there's no Audio or High Fidelity measurement to lean on and no contemporary verdict to quote. What's left is the manufacturer's own spec sheet, which is detailed and internally consistent, and which is also the manufacturer talking about its own product.
For collectors, the CO2 is a working tool and not a fetish object. It's a small, rugged, paint-it-to-match lavalier, and its value comes down to whether it still passes signal cleanly. The permanently attached cable and polycarbonate housing leave little glamour in the construction. The archive has no current market pricing or documented failure patterns to report. Owners of similar Electro-Voice lavaliers tend to judge them on the cable first, since that's the part that ages, and then on whether the electret capsule has held its sensitivity. That's a general pattern and isn't established for the CO2 specifically, so treat it as a caution and not a fact.
Stated without hedging, the CO2 is a 36-gram, 50 Hz - 20 kHz, 100-ohm omni condenser that runs on standard phantom power. It comes with a sensible set of mounting hardware and can be painted to disappear. For a directional mic in a loud room, Electro-Voice's own manual points elsewhere.
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