The Sync Stereo Earmuff can be used as a passive hearing protector or as stereo earmuffs. They protect from most low-to-medium hazardous noise levels while maintaining high-fidelity sound qualities. Technologically advanced acoustical bass chamber enhances bass sounds that are typically sacrificed in industrial stereo earmuffs. Use with most MP3 players, mobile phones and other personal audio devices at work or at home. Volume limiter technology manages output volume. Ease-of-use is enhanced by maintaining volume and power control through the external device. No volume knobs or power switches to coordinate nor batteries to replace. Lightweight and sleek design with comfortable fit to wear during the work day. Includes 3.5mm aux input cable.