Sennheiser • Headphones
Sennheiser HD 660S2
Universal Summary
The HD 660S2 is a driver-level revision of the HD 660S rather than a new headphone. The voice coil was reworked and impedance moves to 300 ohms, matching the HD 600 and HD 650. The low end is the headline change: sub-bass extends further and the mid-bass carries more body than the predecessor, with the missing fundamental in lower-register instruments described as finally present. The tuning still stays measured rather than bass-forward, and it is explicitly not aimed at bass-heads. Tonally it sits between the HD 600 and HD 650 with a lean toward the HD 650, cleaner through the mids than the HD 650 and less forward than the HD 600. Treble is where reviewers split: one account hears considerably more bite, sizzle and crispness than the original without harshness, while another frames the profile as relaxed and deliberately not treble-emphasized. Staging is reported as taller and deeper with more precision than the predecessor, though the presentation is still called intimate rather than expansive. A dip through roughly 3-5 kHz is flagged for dimming detail on some tracks, with a few dB of parametric EQ offered as the remedy. The chassis, velour pads and headband carry over unchanged, and the packaging is judged a downgrade. Value is the real fault line: at a street price near $500 one verdict reads it as a clear technical step up on the HD 660S, while another concludes it does not differentiate itself from cheaper models in the same family and tells existing HD 660S and HD 600 owners to save their money.
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Research Version
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Strengths
- Sub-bass extension and mid-bass body are a clear step up on the HD 660S, with lower-register fundamentals finally landing with weight.
- Tonality sits between the HD 600 and HD 650 with a lean toward the HD 650, reading smooth and even without a heavy treble roll-off.
- Staging gains height and depth over the predecessor with more precise placement, and is called the standout improvement of the generation.
- The 300 ohm load matches the HD 600 and HD 650 and rewards OTL or SETA tube amplification, where the most expansive pairings were found.
- Detachable two-pin cables with 6.3mm and 4.4mm terminations make it easy to re-cable and repair over a long ownership period.
- Weight is low at a rated 260 g with virtually no vertical pressure, so long sessions stay viable once the new-pad clamping settles.
Weaknesses
- A dip through roughly 3-5 kHz dims detail on some tracks, and the fix offered is a few dB of parametric EQ rather than the stock tuning.
- A subtle harmonic dissonance around 5-6 kHz sits over the upper mids and vocals, and EQ lifting the 2-4 kHz region can exaggerate it.
- Lateral clamping pressure is high when brand new, and the velour pads need time in use before they soften.
- The design was not changed for the S2, so the price increase over the HD 660S buys no hardware revision to the chassis, headband or pads.
- Packaging was cut back from the previous generation to a smaller, simpler box that reads as more disposable.
- Fully open, so isolation is effectively nil and outside noise comes straight through.
Best For
- Owners of OTL or SETA tube amplifiers looking for a 300 ohm dynamic headphone to drive
- HD 600 and HD 650 listeners who want the familiar house voicing with more sub-bass underneath it
- Quiet home desktop listening where open-back design and zero isolation do not matter
- Long-session listeners who prefer a smooth, unemphasized treble over sparkle
- Buyers willing to add a few dB of parametric EQ through the upper mids
Measurements
Frequency response
- Sennheiser HD 660S2 (L)
- Sennheiser HD 660S2 (R)
Measured by Kuulokenurkka on squig.link · Measurement © Kuulokenurkka; publicly hosted squig.link data, cited with attribution. Confirm permission before commercial redistribution. · Other / unspecified rig
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What the research says
The HD 660S2 is a driver-level revision of the HD 660S rather than a new headphone. The voice coil was reworked and impedance moves to 300 ohms, matching the HD 600 and HD 650. The low end is the headline change: sub-bass extends further and the mid-bass carries more body than the predecessor, with the missing fundamental in lower-register instruments described as finally present. The tuning still stays measured rather than bass-forward, and it is explicitly not aimed at bass-heads. Tonally it sits between the HD 600 and HD 650 with a lean toward the HD 650, cleaner through the mids than the HD 650 and less forward than the HD 600. Treble is where reviewers split: one account hears considerably more bite, sizzle and crispness than the original without harshness, while another frames the profile as relaxed and deliberately not treble-emphasized. Staging is reported as taller and deeper with more precision than the predecessor, though the presentation is still called intimate rather than expansive. A dip through roughly 3-5 kHz is flagged for dimming detail on some tracks, with a few dB of parametric EQ offered as the remedy. The chassis, velour pads and headband carry over unchanged, and the packaging is judged a downgrade. Value is the real fault line: at a street price near $500 one verdict reads it as a clear technical step up on the HD 660S, while another concludes it does not differentiate itself from cheaper models in the same family and tells existing HD 660S and HD 600 owners to save their money.
Visible Sources
Approved source material
Sennheiser HD 660S2 Review
Three-page subjective review rating the HD 660S2 8.7/10 at $499.95, calling it "a clear technical step up on the HD 660S" with improved sub-bass and a preference for OTL tube amplification.
Sennheiser HD 660S2 review
Scores the HD 660S2 6.3/10, concluding it "doesn't differentiate itself from cheaper options in its product line" and advising HD 660S or HD 600 owners to "save your money".
Sennheiser HD 660S2 Review
Four-page review whose accessible first page covers the coil redesign, the move to 300 ohms, the specification table and pricing, positioning the HD 660S2 against the HD 600 and HD 650.
Sennheiser HD 660S2 Review
Calls the expanded soundstage its "favorite improvement by far" and hears "significantly more bite" in the treble, while accepting it is not unreasonable to skip the $100 price rise.
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