The driver size differs between the two (38 mm vs 45 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. There is a noticeable difference in weight (260 Gm vs 377 GM), which may affect comfort during extended use. Impedance levels vary (300 ohm vs 30 ohm), which can affect compatibility and audio output when used with different devices. The frequency response differs (8 Hz -41500 Hz vs 5Hz - 40KHz), which can influence how well the headphones reproduce lows, mids, and highs. Sennheiser HD 660S2 and Beyerdynamic DT 1770 PRO MKII offer different noise cancellation capabilities (AMBIENT vs NA), which can impact how effectively they block external noise. 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 1770 PRO MKII are well-known options in the wireless headphone segment, offering a balance of audio quality, battery performance, and smart features. Both models support modern Bluetooth connectivity, ensuring stable wireless performance with compatible devices.

Verdict: Both headphones offer strong performance, and the right choice depends on your priorities such as battery life, comfort, and noise cancellation.