Both models support modern Bluetooth connectivity, ensuring stable wireless performance with compatible devices. The driver size differs between the two (38 mm vs 45 mm), which can influence sound depth, bass response, and overall audio clarity. Impedance levels vary (300 ohm vs 30 ohm), which can affect compatibility and audio output when used with different devices. There is a noticeable difference in weight (260 Gm vs 376 GM), which may affect comfort during extended use. Overall, both headphones are feature-rich and cater to users looking for a combination of sound quality, comfort, and wireless convenience. Sennheiser HD 660S2 and Beyerdynamic DT 1990 PRO MKII offer different noise cancellation capabilities (AMBIENT vs NA), which can impact how effectively they block external noise. Both headphones offer solid battery performance, making them suitable for long listening sessions and travel. If you're comparing Sennheiser HD 660S2 and Beyerdynamic DT 1990 PRO MKII, both models offer a strong combination of sound performance, comfort, and modern wireless features. The frequency response differs (8 Hz -41500 Hz vs 5Hz - 40KHz), which can influence how well the headphones reproduce lows, mids, and highs.

Verdict: Choosing between Sennheiser HD 660S2 and Beyerdynamic DT 1990 PRO MKII depends on whether you value better sound, longer battery life, or enhanced features.