Headphones — Sennheiser HD 660 S2

The HD 660 S2 is an open-back over-ear headphone from Sennheiser, an updated version building on the legendary HD 650's design with dual-connector flexibility. The HD 660 S2 brings Sennheiser's more accomplished current engineering to an open-back, over-ear format.

Key specs that matter

The transducer uses dynamic or isodynamic driver technology in an open-back, over-ear, wired configuration. Frequency response spans an exceptionally wide 8Hz to 41,500Hz within plus-or-minus 10dB. Connection offers both 6.3mm and 4.4mm balanced connector options, providing genuine flexibility across single-ended and balanced sources. Sensitivity is 104dB SPL at 1kHz/1mW, with impedance at a demanding 300 ohms - matching the HD 650's requirement for a capable headphone amplifier. Weight is 260g.

Sound and use context

Expect the refined, musically engaging character Sennheiser's legendary open-back heritage is broadly celebrated for, with the demanding 300-ohm impedance requiring a capable headphone amplifier, now with genuine balanced-connection flexibility.

Pairing

The demanding 300-ohm impedance requires a capable headphone amplifier, and the dual 6.3mm/4.4mm connector options let the HD 660 S2 pair directly with either single-ended or balanced sources.

Alternatives

Sennheiser's own HD 650 offers the predecessor model within the same broader legendary open-back catalogue.