Sennheiser HD 660S2: Specs, Features & Buying Guide

The bottom line: The Sennheiser HD 660S2 is the successor to the HD 660S and one of the most refined open-back wired headphones in its class. A 42mm dynamic driver with a vented magnet system delivers the smooth 6-series midrange with noticeably deeper sub-bass than the original — but the 300-ohm impedance means you need a proper headphone amp to hear it at its best. SoundMavericks Score: 8.5/10

Sennheiser HD 660S2 — Key Specifications

What Is the HD 660S2?

Launched in early 2023, the HD 660S2 is Sennheiser’s direct successor to the HD 660S — part of the legendary 6-series lineage that includes the HD 600 and HD 650, headphones that have been reference points for audiophiles for decades. The S2 keeps the same 300-ohm DNA and open-back architecture, but redesigns the transducer system around an airflow-optimized magnet and a more compliant voice coil to extend bass response.

The headline change over the original HD 660S is the low end: sub-bass is deeper and more present, addressing the one area where the classic 6-series sound traditionally held back. Everything else — the natural, relaxed midrange, the fatigue-free treble, the intimate presentation — carries over intact.

Sound Quality: Smooth Mids, Deeper Bass

The HD 660S2 sounds like a 6-series headphone that finally got its bass right. The midrange is the star: vocals and acoustic instruments come through smooth and lifelike, without the sibilance or edge that cheaper headphones smear over everything. Reviewers consistently describe the presentation as intimate and refined rather than flashy.

The treble is deliberately fatigue-free — extended enough to give cymbals and strings real air, but never harsh. Multiple outlets (including What Hi-Fi’s four-star review and HiFi Oasis’s 8/10 rating) praise exactly this quality: you can listen for hours without ear fatigue, and the sound never gets boring.

Where the S2 moves beyond the original HD 660S is sub-bass. Electronic tracks, kick drums, and low synth lines carry more weight and extension. If you love the 6-series sound but always wished for a bit more low-end, this is the model that answers it. For the most demanding wireless listeners, note that no wired headphone offers the codec tricks of high-end Bluetooth codecs — the HD 660S2 trades wireless convenience for pure wired signal path.

Design, Build & Comfort

Build quality is excellent: the open grilles with bronze accents look distinctive, the enclosure uses metal components, and the detachable cable connections are robust. At 260 g the HD 660S2 sits comfortably in the midweight range, and the velour earpads are plush from the first wear.

One common observation across reviews: the clamping force runs strong out of the box. It relaxes with a break-in period, after which comfort is consistently rated very highly. The included carry pouch is serviceable, though reviewers note it feels snug when you try to fit both cables in alongside the headphones.

The Amp Question: Why 300 Ohms Matters

This is the section that matters most for buyers. At 300 ohms with 104 dB sensitivity, the HD 660S2 is not a headphone you can run happily straight from a phone or most laptop jacks. It will make sound from a weak source, but bass will thin out, dynamics will flatten, and you’ll be asking why your audiophile headphone sounds ordinary.

Any decent dedicated headphone amp — desktop or portable — unlocks the full tuning. The high impedance is actually a design choice: it keeps distortion from the thin voice coil low and gives you clean, controlled bass with a proper amp driving it. Budget for an amp in your system cost if you don’t already own one.

Included in the box are a 1.8 m cable with a 6.35 mm plug and a 1.8 m balanced cable with a 4.4 mm plug, plus a 6.35 mm to 3.5 mm adapter — a genuinely generous cable set that covers both desktop and balanced amp setups.

HD 660S2 vs HD 660S vs HD 600 vs HD 650

• vs HD 660S (original): The S2 adds deeper sub-bass and refined treble. If you own the original, the difference is real but incremental — the biggest gain is low-end extension.
• vs HD 600: The HD 600 is leaner and more neutral in the bass, and typically the better value pick for a strictly reference-style listen. The S2 is the more fun, fuller-bodied option.
• vs HD 650 / HD 6XX: The warmer-sounding siblings. The S2 is more detailed and extended at both ends of the frequency range; the 650 family remains the value king if warmth is what you want.

Who Should Buy It — And Who Shouldn’t

Buy it if: you listen at a desk in a quiet room, you already own or plan to buy a headphone amp, and you want the smoothest, most natural midrange under its class with real sub-bass.

Skip it if: you need portability, noise isolation, or wireless connectivity. The open-back design leaks sound in and out — these are not headphones for commuting, open offices, or travel. For those use cases, look at our best noise-cancelling headphones roundup instead. And if you mainly watch TV wirelessly, our best wireless headphones for TV watching guide is the right place to start.

Pros & Cons

Pros:

• Smooth, refined midrange — vocals sound exceptional
• Deeper sub-bass extension than the original HD 660S
• Fatigue-free treble for long listening sessions
• Excellent build quality; generous cable set including 4.4 mm balanced
• Plush, comfortable velour earpads

Cons:

• 300-ohm impedance demands a dedicated headphone amp
• Strong clamping force out of the box
• No Bluetooth, no ANC, no mic — wired home listening only
• Open-back design leaks sound; useless for commuting or travel
• Carry pouch is a tight fit with both cables

Final Verdict

The Sennheiser HD 660S2 is what it claims to be: the classic 6-series sound with the sub-bass the original never quite delivered, wrapped in excellent build quality. It doesn’t try to be a do-everything headphone — no wireless, no ANC, no compromises on the wired signal path. For quiet-room listening with a proper amp, it’s one of the most satisfying headphones in its class, and an easy recommendation for vocal, acoustic, and jazz listeners in particular.

SoundMavericks Score: 8.5/10 — Sound 9.0, Comfort 8.5, Build 8.8, Value 7.6.

Method note: This assessment is compiled from published reviews (TechRadar, What Hi-Fi, HiFi Oasis, reviewatlas) and the verified Amazon product listing — not from hands-on testing. Specs were cross-checked against the manufacturer’s data and the listing’s spec table.

Frequently Asked Questions

Do I need an amplifier for the Sennheiser HD 660S2?

Yes, for the full experience. The 300-ohm impedance and 104 dB sensitivity mean a phone or laptop jack won’t deliver enough clean voltage — bass thins out and dynamics flatten. A dedicated desktop or portable headphone amp is strongly recommended.

Is the HD 660S2 better than the original HD 660S?

It improves on it where it counts: deeper sub-bass extension, refined treble, and a redesigned vented-magnet transducer. The midrange character carries over intact, so existing HD 660S owners will hear a familiar but fuller sound.

Should I buy the HD 660S2 or the HD 600?

Choose the HD 660S2 if you want fuller bass and a slightly more exciting presentation. Choose the HD 600 if you want the leanest, most neutral reference tuning and typically better value. Both need an amp.

Does the HD 660S2 have Bluetooth or noise cancelling?

No. The HD 660S2 is wired only — no Bluetooth, no ANC, no microphone. It’s designed for stationary, high-quality home listening. If you need wireless or noise cancelling, see our best noise-cancelling headphones for travel guide.

Can you use the HD 660S2 without an amp?

It will produce sound from a phone or laptop, but not at its best — low volume headroom and weak bass are typical. You don’t need an exotic amp, but a basic dedicated amp makes a clearly audible difference.

Is the HD 660S2 good for gaming?

It’s fine for single-player atmosphere and casual gaming, with precise but intimate imaging. For competitive gaming, the narrowish soundstage is a limitation versus wider headphones like the HD 800 S, and the open back leaks sound into microphones.

Mark Folksman

I am the founder of Sound Mavericks, where I provide the polite truth about audio equipment. I started this site because consumer electronics reviews are often too technical. Instead of using a silent lab, I test headphones, earbuds, and Bluetooth speakers in the real world – like on a noisy subway or in a busy coffee shop.

To stay independent, I buy my own review units (mostly from the United States) rather than accepting free gifts from brands. Once I finish testing a product, I sell it locally to our community. My goal is to help you understand sound quality, active noise cancellation (ANC), and battery life without the marketing hype.