What to know first
- Redesigned aluminum voice coil now matches the HD 600/HD 650 family at 300 ohms, up from 150 ohms on the original HD 660S
- Sennheiser says the new coil and vented magnet system roughly double sound pressure at the lowest frequencies compared to the HD 660S
- Open-back design means real amplification helps, and there's no isolation from outside noise
- Weighs 260 grams with velour earpads, keeping the clamping force firm but manageable for long sessions
- Ships with both a 6.35mm single-ended cable and a 4.4mm balanced cable, both 1.8 meters, shorter than the original HD 660S's cables
- Fully serviceable: earpads, headband padding, and cables can all be replaced down the line
Where the HD 660S2 sits in Sennheiser's own family tree
The HD 660S2 exists because Sennheiser's own customers pushed back on the HD 660S. That 2018 model made the classic HD 6-series sound easier to drive and a little faster, but longtime fans of the HD 600 and HD 650 missed the low-end weight and dynamics those older headphones carried. The HD 660S2 is Sennheiser's answer: keep the familiar shape and the open-back design, but rebuild the driver so it can put out real sub-bass without losing composure.
It sits directly between the HD 600/HD 650 (still in production after nearly three decades combined) and the HD 800S at the top of the lineup. Announced in February 2023, it remains Sennheiser's current mid-tier open-back model, competing against newer arrivals like the HD 490 Pro on price and specs while drawing on a driver lineage that traces back to 1997.
This isn't a headphone chasing trends. It's built for someone who already knows they like a relaxed, natural tonality and wants Sennheiser to finally give that sound some low-end muscle.
The sub-bass fix that changes how the whole headphone sounds
The headline engineering change is the voice coil. Sennheiser swapped in an ultra-light aluminum coil that raises impedance to 300 ohms, matching the HD 600 and HD 650, up from the HD 660S's 150 ohms. Combined with a more compliant driver surround that Sennheiser says drops the resonant frequency to 70 Hz, the result is roughly double the sound pressure at the very lowest frequencies compared to the outgoing model.
In practical terms, that means bass notes that used to roll off early now carry through with real weight. A five-string bass's lowest note, or the bottom key on a concert piano, actually registers instead of getting implied. Sennheiser's own explanation for why this matters beyond bass fans is worth taking seriously: extending the low end gives the rest of the frequency range more space to work in, which is why the highs are described as sounding more brilliant and the soundstage deeper, even though neither of those ranges technically changed.
Distortion is rated under 0.04% at 1kHz and 100dB, and the frequency response spans 8Hz to 41,500Hz, both figures that track closely with Sennheiser's other HD 6-series models. The point isn't a wider spec sheet, it's that the same driver family finally has the bottom-end extension that critics of the HD 660S were asking for.
Living with an open-back headphone that wants a real amp
Setup is where the HD 660S2 asks something of the owner that a wireless headphone never would. At 300 ohms, it's not designed to sound its best straight out of a phone or laptop jack. Sennheiser includes both a 6.35mm single-ended cable and a 4.4mm balanced cable in the box, plus a 6.35mm to 3.5mm adapter, which signals plainly that this headphone expects to live on a desk next to a dedicated amplifier or DAC/amp combo, not in a bag.
Comfort is where the design earns its keep for long sessions. At 260 grams with velour earpads and an open design, it's light enough to wear for hours without the top of your head complaining, though the clamping force is firm out of the box. The headband is metal under the padding, so you can gently stretch it by hand to loosen the fit if it feels tight, a small but genuinely useful bit of serviceability that plastic-headband competitors don't always allow.
Because it's open-back, sound leaks out in both directions. Anyone in the room will hear what you're listening to, and you'll hear them right back. That's a fair trade for the spacious, unrestricted feeling open designs are known for, but it rules out the HD 660S2 for shared offices, transit, or anywhere quiet is a requirement rather than a preference.
Everything on this headphone is meant to be serviced rather than replaced. Earpads, headband padding, and the detachable two-pin cables can all be swapped without tools, which matters if you plan on keeping this headphone for a decade the way plenty of HD 600 owners already have.
What the extra bass doesn't fix
The 300-ohm impedance is a real commitment, not a footnote. If your only source is a phone, tablet, or a laptop's built-in headphone jack, you're unlikely to get enough clean volume or control out of the HD 660S2 to justify its price. Budget for an amplifier, even a modest desktop one, or this headphone will sound thinner and less controlled than it's capable of.
Open-back also means zero isolation. Commuting, open offices, coffee shops: none of it works with this headphone, and it will leak your music to anyone nearby at moderate volume. If you need something to wear outside a quiet room at home, look at a closed-back or wireless model instead.
The box itself is basic for the price, a soft carry pouch rather than a hard case, and the bundled cables are shorter than the ones that came with the original HD 660S. Neither is a dealbreaker, but if you were expecting a premium unboxing experience to match the sound, temper that expectation.
The specs that matter
The new coil is the reason this model finally has real sub-bass extension compared to its predecessor, without changing the open, airy character the HD 6-series is known for.
This matches the HD 600 and HD 650, and it means a phone or basic laptop output likely won't drive it to its full potential. Plan on a dedicated headphone amplifier.
Combined with the high impedance, this confirms the HD 660S2 is built for amplified desktop listening rather than portable use.
The extended low end (down to 8Hz) is what gives the redesigned driver its added sub-bass weight versus the outgoing HD 660S.
Light enough for multi-hour listening sessions without neck or head fatigue, a real advantage over heavier closed-back or planar alternatives.
Covers most amp setups out of the box, though both cables are shorter than the ones bundled with the original HD 660S.
Serviceability means this headphone can realistically last many years, the same way HD 600 units from the 1990s are still in use today.
Who this product fits
You own an HD 650 and want more bass without changing character
The HD 660S2 is built specifically for you. It keeps the same relaxed, natural midrange Sennheiser's HD 6-series is known for while roughly doubling the sound pressure at the lowest frequencies, giving bass-heavy tracks weight the HD 650 never quite delivered.
You're shopping with only a laptop headphone jack to plug into
The 300-ohm impedance means you won't get this headphone to sound its best without an amplifier. Look at a lower-impedance open-back model, or budget for a modest desktop DAC/amp alongside this purchase.
You want an open-back headphone for a home desk setup
Paired with a decent amplifier, this is exactly the environment the HD 660S2 is designed for: quiet room, dedicated listening time, and no need to isolate outside noise.
You're deciding between this and the newer HD 490 Pro
The HD 490 Pro drives more easily at 130 ohms and folds flat for storage, while the HD 660S2 sticks with the higher-impedance HD 6-series formula and doesn't fold. If portability or easier amp requirements matter more to you than lineage, the HD 490 Pro is important to compare.
What else to compare
A few other Sennheiser and open-back options are worth knowing before you commit.
Sennheiser HD 660S2 FAQ
Does the Sennheiser HD 660S2 need an amplifier?
Yes, practically speaking. At 300 ohms, it's designed for a dedicated headphone amplifier or a DAC/amp combo rather than a phone or laptop jack. Without one, you'll likely hear thinner, less controlled sound than the driver is capable of.
What's different between the HD 660S2 and the original HD 660S?
The HD 660S2 uses a redesigned aluminum voice coil that raises impedance from 150 ohms to 300 ohms, matching the HD 600 and HD 650. Sennheiser says this, combined with a more compliant driver surround, roughly doubles sound pressure at the lowest frequencies for noticeably deeper sub-bass.
Can I use the Sennheiser HD 660S2 for gaming or watching movies?
You can, and the open, spacious soundstage suits movies and game audio well, but the open-back design means anyone nearby will hear your audio, and you'll hear them. It's best suited to a quiet room rather than shared spaces.
Are the earpads and cables replaceable on the HD 660S2?
Yes. The velour earpads, headband padding, and the detachable two-pin cables can all be swapped without special tools, which is part of why earlier headphones in this lineage have stayed in service for decades.
Is the HD 660S2 worth it if I already own the HD 650 or HD 600?
If you're satisfied with your current bass response, it's not an urgent upgrade. If you've always wished those headphones had more low-end extension while keeping the same midrange character, the HD 660S2 is built for exactly that complaint.
Who actually needs the extra bass
Sennheiser didn't reinvent the HD 6-series with the HD 660S2, and it didn't need to. What it did was fix the one complaint that followed the HD 660S around since 2018: not enough low-end weight. The redesigned voice coil and magnet system deliver real, measurable sub-bass extension without disturbing the calm, accurate midrange this lineage has built its reputation on since the HD 580.
Buy this if you want an open-back headphone for a quiet room, you're willing to pair it with real amplification, and you've always liked Sennheiser's house sound but wanted more bottom end. Skip it if you need portability, isolation, or an easy match with a phone. For everyone else already invested in this sound signature, the HD 660S2 is the version that finally rounds it out.