Both models support modern Bluetooth connectivity, ensuring stable wireless performance with compatible devices. Overall, both headphones are feature-rich and cater to users looking for a combination of sound quality, comfort, and wireless convenience. Impedance levels vary (32 Ohms vs 300 ohm), which can affect compatibility and audio output when used with different devices. There is a noticeable difference in weight (310 g vs 260 Gm), which may affect comfort during extended use. 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. Denon AH-MM400 and Sennheiser HD 660S2 are premium wireless headphones designed to deliver high-quality sound along with advanced features like noise cancellation and long battery life. The driver size differs between the two (40 mm vs 38 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. Denon AH-MM400 and Sennheiser HD 660S2 offer different noise cancellation capabilities (Yes vs AMBIENT), which can impact how effectively they block external noise.

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