Despite the HD 660Ss standing as one of the worlds popular audiophile headphones, some customers nevertheless wanted one very specific enhancement: even deeper bass. Because whether its a thunderous crescendo of timpani or the pulsating beat of electronic dance music, there is nothing like accurate, powerful sub bass to infuse your listening with drama. Audiophilesand anyone looking for comfortable, non-fatiguing, high-end headphonescan now get even more impact and emotion from the HD 660S2. The headphones warm, relaxed tone is reflected by their timeless styling with elegant bronze accents. With its open-back design and outstanding comfort, the HD 660S2 is also destined to be a favorite for long listening sessions. This version builds on all the strengths of its formidable predecessor. The same world-class precision and resolution still let you pick out individual instruments like with no other headphone. Or experience the joy of discovering sonic details in recordings youve known for yearsnow underscored with more and deeper low end. Indeed, the standard-setter for extended listening has now become the standard-setter for extended bass as well. Enhancing this heralded audio design without detracting from its many strengths was, however, a daunting task. So, our engineers set out to systematically identify and exploit every opportunity in their quest to improve on the acclaimed HD 660S design. We adjusted the compliance of the surround, for instance, dropping the resonance frequency to 70 Hz. Considerable effort went into optimizing the airflow around the transducer. The coil in the HD 660S2 has also been revised to match the legendary HD 600 & 650, resulting in an impedance of 300 ohms. The coil offers a high magnetic force and electrical damping for a clean impulse response. It also increases sensitivity over the entire frequency spectrum by using the magnets air gap more efficiently. Taken together, these efforts and more have paid off in spades. Sound pressure at the lowest octaves has doubled. Now, you can feel the music more than ever beforewith all the depth and weight that ultra-low frequencies invoke. The lowest A on the piano (27.5 Hz) or the pounding root note of a bass drum (45-60 Hz) are just as big, expansive, and imposing as if they were live. The unique combination of impactful bass combined with the warm tuning and smooth treble will be a revelation for audiophile listeners. Its an even better way to lose yourself in comfortable, non-fatiguing, high-end soundwhile feeling its full low-end power.