Sennheiser HD 660S2

The HD 600 Lineage With More Bass

The 660S2 sits in the same family as the HD 600 and 650 and shares their essential character: neutral, midrange-honest, comfortable, repairable. What it adds is meaningfully extended sub-bass.

The HD 600 rolls off in the very low frequencies, which is part of why it sounds so clean and part of why electronic music and film soundtracks can feel lacking on it. The 660S2 extends further down with real weight rather than a boosted bass hump.

That is a genuine improvement for a substantial part of what people listen to, and it is achieved without turning the headphone into a bass-forward consumer tuning.

Lower Impedance, Easier To Drive

The impedance is considerably lower than the HD 600's, which means it is easier to drive to a proper level from modest sources.

It still benefits from a decent amplifier — the sub-bass extension in particular needs current to be controlled — and the gap between "adequate" and "good" is narrower than with the older models. A competent portable DAC will do a reasonable job.

For anyone who wants the family character without committing to a desktop amplifier, that shift is the practical argument for this model over the HD 600.

Where The HD 600 Still Wins

Price, straightforwardly. The HD 600 costs considerably less and retains the midrange that made the family famous, and for vocal and acoustic music the difference between them is small enough to be a matter of taste.

The HD 600 is also the better reference for mixing precisely because of its bass roll-off — it does not flatter low-frequency content, so problems down there are more apparent rather than less.

Anyone choosing between them should be honest about what they listen to. For electronic, orchestral and film content the 660S2 is clearly better; for jazz, folk and podcasts the HD 600 is a better purchase at a lower price.

Comfort And Parts

It shares the family's comfort, which is to say excellent for multi-hour listening, with a light clamp and deep velour pads.

Parts remain replaceable, which is the underrated reason to buy into this family at all — a headphone with available pads, cables and headbands stays usable for decades rather than becoming landfill when a pad splits.

It remains open-back, with everything that implies: no isolation, complete leakage, unusable around other people.

Against The Alternatives

Against the HD 600, this adds sub-bass and easier drivability at a higher price; the HD 600 is a better value reference for acoustic music.

Against the HIFIMAN Sundara, the planar has tighter bass control and the Sennheiser has a more natural midrange and more consistent build quality.

Against closed headphones, the usual open-back trade applies and cannot be worked around.

Anyone needing isolation should not buy any open-back headphone.

Anyone listening mainly to acoustic music and voices should buy the HD 600 and save the difference, since that is where the two are closest.

Anyone mixing bass-heavy material may actually prefer the HD 600's roll-off, as it flatters low-end problems less.

The Verdict

The right choice in the HD 600 family for anyone listening to electronic, orchestral or film content, adding real sub-bass extension without abandoning neutrality, and easier to drive than its predecessors.

It costs considerably more than the HD 600, which remains excellent, and it is still an open-back headphone with no isolation.

If you mostly listen to acoustic music and voices, buy the HD 600 instead — the gap is small and the price gap is not.