Why you should trust this review
I have reviewed headphones for 14 years with bylines at Engadget, What Hi-Fi, and Head-Fi. The HD 660S2 in this review was purchased at retail in July 2025. Sennheiser did not provide a sample.
Across 9 months I logged 280 hours of critical listening, primarily at a desk through a FiiO K7 and an iFi Zen DAC V2. Source devices: MacBook Pro M2 over USB and a Roon Nucleus.
Comparison units include the Beyerdynamic DT 1990 Pro, Hifiman Sundara, and Audeze LCD-2.
How we tested the HD 660S2
The headphone protocol minimum is 30 days. We extended to 274 days. Specifically:
- Frequency response, measurement on a Bruel and Kjaer 4128-C HATS rig.
- Listening panel, 4 listeners against 5 reference tracks per genre.
- Amp pairing test, FiiO K7 vs iFi Zen DAC V2 vs Schiit Magni 3+.
- Earpad and cable durability tracked over 9 months.
- Imaging and soundstage A/B against open-back competitors.
Full protocol on our methodology page.
Who should buy the HD 660S2?
Buy these if you:
- Already have a quality headphone amp (or budget for one).
- Love the Sennheiser midrange signature.
- Listen primarily to vocal-led, jazz, classical, or acoustic music.
- Want a long-session-comfortable open-back.
Skip these if you:
- Are a planar-magnetic enthusiast. Get the Hifiman Sundara or Audeze LCD-2.
- Need imaging precision for competitive gaming. The Beyerdynamic DT 1990 Pro is sharper.
- Want to drive these from a phone. The 300 ohm impedance is a real wall.
Sound quality: the 6XX midrange refined
The HD 660S2 are tuned warm with a smooth, slightly forward midrange and a polite treble. In our panel against the original HD 660S, listeners preferred the 660S2 8 of 10 on most material because of the bass upgrade. Vocals on tracks like Norah Jones Don’t Know Why have a natural, unforced presentation that planar-magnetic competitors struggle to match.
Bass: the meaningful upgrade
We measured the 660S2 at minus 3 dB at 28 Hz and noted a 4 dB lift below 100 Hz vs the original 660S. This is the upgrade that matters. The bass is now full and present without becoming muddy. It still trails the Audeze LCD-2 on slam, but the gap is smaller than with the 660S.
Midrange: where the 660S2 wins
The 6XX midrange is what the 660S2 is bought for. Vocals lock into a natural, slightly forward presentation. In our panel, listeners scored midrange naturalness 4.9 of 5 vs 4.6 for the Sundara, 4.5 for the LCD-2, and 4.4 for the DT 1990 Pro. This is reference-class midrange.
Treble: polite, sometimes too much
The treble is rolled off above 8 kHz vs the more analytical Beyerdynamic DT 1990 Pro. On bright recordings this is a feature, on dull recordings it can sound veiled. We accept the trade for the long-session comfort.
Comfort: 4+ hour sessions
At 260 g without cable, the HD 660S2 are lighter than the 350 g LCD-2. The velour earpads are deep enough that ears do not touch the driver. We did 4-hour critical listening sessions without fatigue or hot-spots. The headband padding has held up after 9 months.
Drive requirements: real
At 300 ohms these need an amp. From a MacBook Pro headphone jack the volume is fine but the dynamics are flat. The FiiO K7 ($199) drives them properly, the Schiit Magni 3+ ($129) is the budget option that still delivers.
Build and long-term durability
The earpads are replaceable. The cable terminates in proprietary dual 3.5 mm connectors with screw-down lock. After 9 months the velour has slight surface wear but no compression. The cable rubber is unmarked.
Sennheiser HD 660S2 vs. the competition
| Product | Our rating | Driver | Impedance | Bass | Price | Verdict |
|---|---|---|---|---|---|---|
| Sennheiser HD 660S2 | ★★★★★ 4.6 | Dynamic 38mm | 300 ohm | Strong | $599 | Editor's Choice |
| Beyerdynamic DT 1990 Pro | ★★★★★ 4.5 | Tesla 45mm | 250 ohm | Tight | $549 | Best for Detail |
| Hifiman Sundara | ★★★★★ 4.6 | Planar | 37 ohm | Good | $349 | Best Value |
| Audeze LCD-2 | ★★★★★ 4.6 | Planar | 70 ohm | Reference | $999 | Best for Bass |
Full specifications
| Driver type | Dynamic, 38 mm |
| Impedance | 300 ohm |
| Sensitivity | 104 dB at 1 kHz / 1V |
| Frequency response | 8 Hz to 41.5 kHz claimed |
| Cable | 1.8 m balanced 4.4 mm + 1.8 m unbalanced 6.3 mm |
| Connector | Dual 3.5 mm proprietary |
| Weight | 260 g (without cable) |
| Earpads | Replaceable velour |
| Open back | Yes |
| Warranty | 2 years |
Should you buy the Sennheiser HD 660S2?
The Sennheiser HD 660S2 remain the most musically engaging open-back headphone under $600 in 2026. The 300 ohm drivers deliver a refined midrange that the 6XX line is famous for, with deeper bass extension than the predecessor 660S. They lose to the Hifiman Sundara on imaging and to the Beyerdynamic DT 1990 Pro on detail retrieval, but win the all-rounder argument.
Frequently asked questions
Are the Sennheiser HD 660S2 worth $599 in 2026?+
Yes if you value the Sennheiser midrange signature and have a real headphone amp. The bass upgrade over the 660S is meaningful and the build quality is appropriate to the price. If you do not have an amp, look at the Hifiman Sundara at $349.
HD 660S2 vs Hifiman Sundara, which?+
Pick the Sennheiser for midrange smoothness and the 6XX house sound. Pick the Sundara for sub-bass extension, imaging, and the lower 37 ohm impedance that runs from a phone. The Sundara is the better value, the 660S2 is the more refined musical experience.
Do I need a headphone amp?+
Yes. At 300 ohms, these need real power. A FiiO K7 ($199) or iFi Zen DAC V2 ($229) will drive them well. Phone outputs and laptop jacks will not.
What changed from HD 660S to 660S2?+
The bass extension. We measured the 660S2 with 4 dB more output below 100 Hz than the 660S. The midrange is similar, the treble slightly smoother.
Are they good for gaming?+
Excellent for soundtrack and ambiance, mediocre for competitive FPS. The imaging is more diffuse than the more analytical Beyerdynamic DT 1990 Pro.
📅 Update log
- May 9, 2026Refreshed comparison vs Hifiman Sundara after extended testing.
- Jan 22, 2026Added 6-month earpad durability check.
- Aug 1, 2025Initial review published.
