Sennheiser HD 660S2

Open-back dynamic reference headphone with extended sub-bass and natural tonality

Features

• Unique ventilated magnet system designed to minimize distortion
• Immersive listening with vivid timbre and deep, precise sub-bass
• Outstanding quality engineered in Germany and manufactured in Ireland
• Featherweight aluminum voice coil with 300-ohm impedance and fast, responsive behavior
• Soft, conforming ear pads and an open design for maximum long-term comfort

Your New Desert-Island Headphone

Every high-end headphone has its own personality. What if you could only own one?

Have you ever felt goosebumps because the sound was so real it seemed like the source was in the room with you? The HD 660S2 gives music lovers an intimate way to experience their favorite songs and artists even more deeply. Stunning resolution and precision bring you closer than ever to instruments and vocals — while keeping the presentation natural and balanced, never harsh or shrill.

That warm, inviting character, combined with extended sub-bass, makes listening uniquely satisfying. And with comfort this high, you’ll quickly find yourself wanting endless sessions. The HD 660S2 brings together the best of many worlds — for an intimate experience you won’t want to give up.

Sub-bass Expands the Entire Soundstage

Double the sub-bass elevates your listening experience.

Traditionally, audiophiles haven’t been the biggest fans of sub-bass. It can easily become loose, boomy, and distracting. And that’s a shame — because there’s so much more down there than just the punch of a kick drum. Did you know the low B of a 5-string bass vibrates at 30.9 Hz? Or that the lowest note of a concert grand is 27.5 Hz? And of course, deeper sub-bass can make bass-heavy genres sound phenomenal.

Here’s the trick: by doubling the sound pressure at the very lowest frequencies, Sennheiser still maintains exceptional precision and balance — in the sub-bass, mid-bass, and beyond. Most impressive is how this changes the overall presentation: extending the low end creates more “space” for the music. Against a deeper backdrop, treble feels more brilliant, the stage deeper, and the emotional impact stronger.

They Feel as Good as They Sound

Cozy slippers, your favorite jeans, the HD 660S2 — some things just feel right.

The HD 660S2 velour ear pads are a tactile pleasure. With just the right amount of clamp for optimal acoustic positioning and supple padding, the headband stays out of the way of the music. As an open-back headphone, the HD 660S2 also keeps your ears in a pleasantly breathable climate — even during very long sessions.

The low overall weight and ergonomically shaped headband help prevent hot spots or discomfort. Combined with excellent “Made in Ireland” build quality, you’ll quickly get used to a listening experience that’s as relaxing as the warm, non-fatiguing sound it’s built around.

How Do You Outdo a Line of Legends?

Some of the world’s most neutral headphones are hard to surpass.

Starting with the HD 580, Sennheiser’s high-end open-backs have impressed generations with balanced, natural reproduction. The HD 600, HD 650, and HD 660S are widely considered benchmarks for neutral audiophile sound — and the HD 660S2 clearly shares that DNA. For example, the revised S2 voice coil now matches the 300-ohm impedance of the legendary HD 600 and HD 650. This new coil also delivers higher magnetic force and electrical damping for a cleaner impulse response.

The surround is now more compliant, lowering resonance frequency to 70 Hz. Significant effort was also put into optimizing airflow around the transducer. With the magnet gap now working more efficiently, sensitivity is higher across the entire frequency range. Together, these changes result in greater precision, speed, and resolution — with double the sound pressure in the very lowest frequencies.

Technical Specifications

Measurements

What does this mean?

The black line represents what could be called an “ideal” curve of how a headphone should sound. The Harman Research Group conducted scientific studies on audio and human perception, asking: how should a headphone be tuned to be preferred by the majority of listeners, regardless of age or other demographic variables? The result is known as the Harman target.

From left to right you see sub-bass, bass, mids, and then the curve finally tilts upward as treble begins — a part of the spectrum naturally amplified by the shape of the human ear.

Yes, the bass roll-off typical of open dynamic headphones is still there — but compared to the HD 650, it really is about twice as loud. That means if you want to boost bass further with EQ, you can do so with lower risk of introducing distortion.

Midrange is excellent: even, resolving, and clear. Treble is relaxed yet still airy and detailed. Overall, it’s a very rounded presentation and a genuinely enjoyable listen.

Harman Research

The Perception and Measurement of Headphone Sound Quality – What Do Listeners Prefer?