While the HD 660 S features the same open-back, matte-black design and frequency response as its predecessor (10Hz-41kHz), Sennheiser claims it has improved this new reference model’s design over the HD 650’s in a few ways. The HD 660 S is made with specific, hand-picked materials and features an improved transducer design to reduce harmonic distortion. Each transducer is paired and placed in the headphones by hand. They are controlled by a stainless steel fabric diaphragm and are coupled with aluminum voice coils, all of which Sennheiser claims to produce the most “lifelike sound” possible.
Sennheiser also dropped the impedance on the HD 660 S to 150 ohms — down from the 300-ohm impedance of the HD 650. This means the HD 660 S can be used with a wider range of products, including both stationary audio equipment like audio-visual receivers and headphone amps, or portable hi-fi audio players like the Astell & Kern Ak70 MK II. While the open-back design makes the HD 660 S better suited for quieter listening environments, having the ability to more easily listen on the go is nonetheless exciting.
Not only has the HD 660 S been designed for better sound and device compatibility, it has also been tailored for comfort during long listening sessions. The earcups and headband both sport generous padding, and the earcups feature an elliptical shape and are angled to fit more naturally with the shape of the ear. The earcup padding can also be removed for cleaning or swapped with different fabric types for customizable comfort (though no extra padding options are included in the retail package).
The HD 660 S will ship with a detachable, oxygen-free copper wire that ends in a gold-plated quarter-inch plug, another cord for DAC connections, which itself ends in a 4.4mm stereo plug, and a quarter-inch to 3.5mm adapter piece. The entire package will be available in mid-October and will retail for $500. You can read more at the HD 660 S’ official web page.
