Headset for wireless The Crown CM-311A is the industry standard headworn electret condenser microphone. The CM-311A utilizes Crown's unique Differoid technology, effectively isolating desired vocals from unwanted background noise. Differoid Noise Canceling Technology Differoid noise canceling rejects ambient signal at a distance, improving signal-to-noise ratio. Filters Electronically controlled bass roll-off Power 48-volt Phantom Powered or 9-volt Battery Lightweight Headset Design Behind-the-ear design is completely lightweight, adjustable, and will conform to any size head.