Back in 2017, German audio specialists Sennheiser launched a successor to its open-back mid-range audiophile champions, the mighty HD 650 headphones. The company has now responded to user feedback and injected more low-end goodness into the updated HD 660S2 cans.
"Our new Sennheiser HD 660S2 offers listeners what they requested most from the headphones’ predecessor," said Sennheiser's Audiophile Product Manager, Jermo Koehnke. "With precision and power like no other and new sensitivity across all frequencies, listeners will hear details they’ve never heard before, especially at the lower end of the spectrum."
The company says that listeners will enjoy the familiar signature reference-level detail across the entire frequency range, but can expect more presence in the lower registers – right down to 8 Hz.
The airflow around the 38-mm transducers has been optimized thanks to a new vented magnet setup to nip distortion in the bud while making for more dynamic playback. Some weight has been shaved off the voice coil too, for an improved impulse response.
The resonant frequency has been lowered from 110 Hz in the HD 660S headphones to 70 Hz "for hefty kick drums that move with ease" and the sound pressure at the lowest frequencies has been doubled to maintain "extraordinary precision and balance throughout the sub bass, mid-bass, and beyond."
In addition to diving lower than before, the frequency response has also been extended slightly to 41.5 kHz, but sensitivity and total harmonic distortion remain unchanged at 104-dB and less than 0.04%, respectively. The headphones also rock a cushioned headband and comfy earpads for long-haul enjoyment of the expansive soundstage.
Sennheiser has designed the new headphones to be versatile enough for plugging into vintage and modern audio systems via the supplied cables and adapters, though users may prefer to find a quiet spot in the house before doing so as the open design means that music will leak out and ambient noise leech in.
The HD 660S2 headphones are available for per-order now for US$599.95, with sales due to kick off from February 21.
Product page: Sennheiser HD 660S2