Both headphones offer solid battery performance, making them suitable for long listening sessions and travel. Overall, both headphones are feature-rich and cater to users looking for a combination of sound quality, comfort, and wireless convenience. There is a noticeable difference in weight (310 g vs 260 Gm), which may affect comfort during extended use. The driver size differs between the two (40 mm vs 38 mm), which can influence sound depth, bass response, and overall audio clarity. Denon AH-MM400 and Sennheiser HD 660S2 offer different noise cancellation capabilities (Yes vs AMBIENT), which can impact how effectively they block external noise. If you're comparing Denon AH-MM400 and Sennheiser HD 660S2, both models offer a strong combination of sound performance, comfort, and modern wireless features. Impedance levels vary (32 Ohms vs 300 ohm), which can affect compatibility and audio output when used with different devices. The frequency response differs (10 Hz - 40,000Hz vs 8 Hz -41500 Hz), which can influence how well the headphones reproduce lows, mids, and highs. Both models support modern Bluetooth connectivity, ensuring stable wireless performance with compatible devices.

Verdict: Both models are competitive, and your decision should be based on your usage needs and preferred features.