Sennheiser HD 660S2: Studio-Quality Sound

Sennheiser is well aware of the HD 660S’s market position and has therefore intentionally made careful updates. It retains its open design and robust dynamic drivers with a diameter of 38 millimeters. These features have earned the headphones an excellent reputation in recording studios. Due to its balanced and detailed sound profile, the HD 660S is virtually indispensable in the realms of mixing and mastering. The key features of the HD 660S2 thus remain untouched. However, the Sennheiser engineers have made slight adjustments to the sound profile. The focus is on the sub-bass, frequencies so low that they are typically not heard but rather felt physically. Here, Sennheiser has turbocharged the HD 660S2. Frequencies from about 50 Hz down to 8 Hz (!) are to be reproduced with double the sound pressure compared to its predecessor. This was achieved through improved aluminum voice coils that are lighter, thus reducing moving mass.

Weighing just 260 grams, the HD 660S2 is light. Thanks to the oval design of the capsules, the headphones continue to offer a comfortable fit, even during long listening sessions, which we can confirm from our test. The ear cushions are covered with velour, contributing significantly to the comfort. The only issue we found in our test was the relatively high clamping pressure of the headphones. Music enthusiasts with particularly large heads might find this problematic. The open design is famous for its playful and lively sound, but it also has the downside of letting in external noises, which can hinder undisturbed playback in certain environments. In the studio, this is usually not a problem, but at home or on the go, one should be aware of this. Sounds, like those from a moving underground train, penetrate quite clearly.

Clever: The cable is easily replaceable with just two simple steps, allowing for hassle-free replacement if it ever gets damaged. Great: The manufacturer includes two cables, giving the HD 660S2 flexible usability. In addition to the obligatory 6.3-mm jack cable (an adapter for a 3.5-mm jack is also included for mobile use), the owner receives a balanced cable with a Pentaconn connector. This highlights the studio genes of this headphone series. The impedance of 300 Ohms also allows for mobile use with a smartphone. The volume was always sufficient in our test. For those who want to transport it frequently, a simple fabric bag is provided, but a sturdy hardcase must be purchased separately.

Sound Quality

In our test, the Sennheiser HD 660S2 Hi-Fi headphones offered a tonally balanced sound quality with an earthy deep bass that was not excessive. The bass formed the foundation of the overall sound impression, giving the music a natural tone. The midrange and lower treble were beautifully transparent, conveying a wide soundstage, while the upper treble produced lively impulses. The sound was incredibly precise and detailed, with clarity and consistency that excellently reproduced every music genre. The HD 660S2 delivered an extraordinary soundstage with excellent separation of instruments.

Versatility

It quickly became clear in our test that the Sennheiser HD 660S2 is suitable for a wide range of music genres. Whether we played pop, rock, jazz, or classical music, the HD 660S2 always delivered impressive results, with every detail of the music audible and never becoming tiring or overly analytical. We were so impressed that we used the HD 660S2 for mastering the current AUDIO magazine CD and the CD of our sister publication, stereoplay. The results are there for everyone to hear.

Conclusion

This headphone speaks primarily one language: Sound! Everything about it is geared towards optimal music reproduction. Every detail becomes “visible”, every playing error is ruthlessly exposed. Plus, the enormous enjoyment it brings always puts a smile on my face when I feed it jazz, funk, or fusion.