CROWN CM-311A
Service Manual

DIFFEROID® HEAD-WORN

CM-311A CM-311A/E
esigned for touring sound, the Crown CM-311A is a rugged head-worn microphone designed for musicians or sportscasters. It sounds like the best handheld microphones� full, clear, and distortion-free, even with the loudest singers.

CONDENSER MICROPHONE

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The CM-311A is the latest version of the patented Differoid® technology. Its cardioid pickup pattern rejects sounds from the rear, such as floor monitors. And its noise-canceling ability rejects sounds at a distance, such as floor monitors, instruments on stage, and crowd noise. In fact, the CM-311A has outstanding gain-beforefeedback and isolation. Lightweight and comfortable, the mic�s headband and boom adjust to fit any singer. An included pop filter greatly reduces breath noise and pops. Because of the boom�s unique behind-the-ear design, it does not cover up the singer�s face.

Specifications
Transducer type: Electret condenser. Frequency response (typical): 50 Hz to 17,000 Hz (see Fig. 1). Polar pattern: Cardioid (see Fig. 2). Impedance: CM-311A, 75 ohms balanced. CM-311A/E, 6 kilohms unbalanced. Recommended load impedance: CM-311A, 1000 ohms or greater. CM-311A/E, 10 kilohms. Open-circuit sensitivity, typical, closetalking: CM-311A, 4 mV/Pa* (-48 dB re 1V/Pa), CM-311A/E, 1.25 mV/Pa (-58 dB re 1V/Pa). Power sensitivity, typical, close-talking: CM-311A: -42.5 dB re 1 mW/Pa*, CM-311A/E: -71.5 dB re 1 mW/Pa. Equivalent noise level (self noise): 26 dB SPL typical (0 dB = 0.0002 dyne/cm2), A-weighted. S/N ratio: 68 dB at 94 dB SPL. Maximum SPL: CM-311A, 148 dB SPL produces 3% THD. CM-311A/E, 140 dB SPL with 3V DC, 148 dB SPL with 9V DC. Operating voltage: CM-311A, 9V DC internal alkaline battery or 18-48V phantom power. CM-311A/E, 3�9V DC from the transmitter�s battery. Polarity: Positive pressure on diaphragm produces positive voltage on CM-311A XLR pin 2 with respect to pin 3, and on CM311A/E shield with respect to white lead. Current drain: CM-311A, 5 mA nominal. CM-311A/E, 0.27 mA nominal. Battery life: CM-311A, 110 hours. CM-311A/E, approximately equal to transmitter battery life. Output connectors: CM-311A, 3-pin pro audio (XLR type). CM-311A/E, supply your own to match your transmitter. Cables (CM-311A): 2-conductor shielded, unbalanced cable, 42 inches from headband to battery pack. Use 2-conductor shielded mic cable (not included) between XLR connector and mixer mic input. Cable (CM-311A/E): In-line with this cable is a small circuit module that equalizes the microphone signal. Cable is 42 inches long from headband to module, 12 inches from module to cable end. 2-conductor shielded unbalanced cable, unterminated. Materials: High-impact plastic mic housing, brass boom, steel wire headband, highimpact plastic and steel battery pack. Finish: Satin black. Net weight: Head-worn mic, 2.1 oz (61 g). CM-311A belt pack and battery, 6.1 oz (173g). Dimensions: Headband 5.5" diameter, adjustable. Boom approximately 7" x 3". See Figs. 3 and 4. Included accessories: Microphone carrying case, WS-6 foam pop filter, clothing clip. Optional accessories: PH-4B phantom power supply (4 channels, AC powered). PH-1A phantom power supply (1 channel, battery or AC-adapter powered). WS-14 accessory windscreen. *1 pascal = 10 dynes/cm2 = 10 microbars = 94 dB SPL.

Two models are available: CM-311A and CM-311A/E. The CM-311A is powered by a 9V battery or phantom power. It has a battery belt pack (AdaptaPack®) with a battery on/off switch, a programmable mic on/off switch, and a �Mic On� LED. The CM-311A/E has no connector; you connect it to a wireless transmitter of your choice.
How to adjust for best fit and to prevent boom bounce To get all the performance you paid for with this microphone, take the time to adjust it to fit correctly. You�ll be glad you did! For best results, the CM-311A MUST be custom fitted to one wearer�s head. This simple procedure takes only a few minutes. Please refer to Fig. 5 and locate the parts described. 1. If the microphone is for yourself, we suggest that you use a mirror to double check the fit as you make adjustments. 2. Loosen (just a little) the thumbscrew located on the outside of the foam block, part way back on the boom. This allows the boom to slide in and out, and to rotate left and right.