The frequency response differs (8 Hz -41500 Hz vs 5Hz - 45KHz), which can influence how well the headphones reproduce lows, mids, and highs. There is a noticeable difference in weight (260 Gm vs 265 GM), which may affect comfort during extended use. Impedance levels vary (300 ohm vs 40 ohm), which can affect compatibility and audio output when used with different devices. Sennheiser HD 660S2 and Audio Technica ATH-AD2000X are well-known options in the wireless headphone segment, offering a balance of audio quality, battery performance, and smart features. In general, both options are suitable for everyday use including music, calls, travel, and work-from-home scenarios. The driver size differs between the two (38 mm vs 53 mm), which can influence sound depth, bass response, and overall audio clarity. Both headphones offer solid battery performance, making them suitable for long listening sessions and travel. Both models support modern Bluetooth connectivity, ensuring stable wireless performance with compatible devices. Sennheiser HD 660S2 and Audio Technica ATH-AD2000X offer different noise cancellation capabilities (AMBIENT vs Active Noise Cancellation), which can impact how effectively they block external noise.

Verdict: Choosing between Sennheiser HD 660S2 and Audio Technica ATH-AD2000X depends on whether you value better sound, longer battery life, or enhanced features.