Measured in ohms, and symbolized as Ω, this quantifies how easily the speaker drivers are to 'drive' – vibrate – sound waves into your ear. Headphones with a low impedance (below 50 ohms) are easy to drive and don't require additional sound amplification above and beyond what your camera or laptop can produce. High impedance headphones are designed for use with a dedicated headphone amp or pro studio equipment, otherwise they can sound too quiet. On our list, we're only recommending low impedance models to ensure maximum device compatibility.