The Sennheiser HD 660S2 are the next generation of the Sennheiser HD 660 S and are open-back audiophile headphones. While they look and feel similar to their predecessor, the manufacturer has re-tuned their sound to deliver a bit more thump, punch, and warmth. Their treble range has also received some sculpting, though this change may be a hit or a miss, depending on if you've previously enjoyed the more balanced sound from other Sennheiser headphones like the Sennheiser HD 650. In addition, their impedance has risen from 150 ohms to 300 ohms (with a sensitivity of 104 dB/SPL), so you'll need a powerful amp to drive them effectively.
Our Verdict
The Sennheiser HD 660S2 are very good for neutral sound. They have a warm sound profile and, despite being open-back, pack more thump and rumble than their predecessor. Their exceptionally neutral mids also ensure that vocals and instruments sound natural and present. A dip in the low-treble hurts the clarity and detail of these sounds, while the following peak in the mid-treble makes sibilants sound more aggressive and piercing, comparatively. Their soundstage, which feels spacious and open, struggles to produce an out-of-head audio experience too, and you'll need an amp to power these over-ears. On the upside, they deliver bass and treble consistently across reseats.
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Consistent audio delivery.
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Well-built and decently comfortable fit.
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Mediocre passive soundstage.
The Sennheiser HD 660S2 aren't designed for commute and travel. They're open-back audiophile headphones, meaning they won't block out the rumbles of bus engines or passenger chit-chat. They're also designed to leak a lot of audio, even at normal volumes, need an amp to be driven properly, and aren't exactly the most portable in design. On the upside, they're decently comfortable.
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Well-built and decently comfortable fit.
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Aren't designed to block out background noise.
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Leak a lot of audio.
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Bulky and wired design can get easily snagged on something.
The Sennheiser HD 660S2 aren't intended for sports and fitness. They're audiophile headphones and can easily fall off your head while you're exercising. Their audio cable can also snag on something and pull them off of your head.
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Well-built and decently comfortable fit.
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Can move around or fall off with large head movements.
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Bulky and wired design can get easily snagged on something.
The Sennheiser HD 660S2 are poor for office use. While they have a decently comfortable fit, they're still open-back headphones, which aren't suitable for a shared workspace. They leak a lot of audio by design, even at lower volumes, which can bother others around you, and they won't block out any noise around you. However, if you have a private office or work from home, they aren't a bad choice if you care about audio quality, provided you don't need to use them to make calls since they don't have a mic.
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Well-built and decently comfortable fit.
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Aren't designed to block out background noise.
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Leak a lot of audio.
The Sennheiser HD 660S2 are wired headphones, and you can't use them wirelessly.
The Sennheiser HD 660S2 are passable for wired gaming if you don't need mic support. They have a warm sound profile that helps emphasize sound effects like footsteps in your gameplay and dialogue, as well as instruments sound natural and present. The headphones are also decently comfortable, though their clamping force may bother you over time if you have a wide head or wear glasses.
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Well-built and decently comfortable fit.
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Mediocre passive soundstage.
The Sennheiser HD 660S2 are audiophile headphones and don't have a built-in mic. If you're using a standalone mic, remember that their open-back design isn't intended to block out background noise.
- 7.9 Neutral Sound
- 3.6 Commute/Travel
- 5.4 Sports/Fitness
- 4.2 Office
- 4.3 Wireless Gaming
- 6.4 Wired Gaming
- 1.5 Phone Calls
- Updated Mar 29, 2024: We've added a comparison between these headphones and the Sennheiser HD 490 Pro in Comfort.
- Updated Mar 08, 2023: Review published.
- Updated Mar 02, 2023: Early access published.
- Updated Feb 28, 2023: Our testers have started testing this product.
- Updated Feb 23, 2023: The product has arrived in our lab, and our testers will start evaluating it soon.
- Updated Feb 21, 2023: We've purchased the product and are waiting for it to arrive in our lab.
Differences Between Sizes And Variants
The Sennheiser HD 660S2 come in one color variant: 'Black' and you can see our model's label here. If you come across another variant of these headphones, please let us know in the discussions, and we'll update our review.
Compared To Other Headphones
The Sennheiser HD 660S2 are open-back headphones and are the successor of the Sennheiser HD 660 S. They have an updated sound that delivers more bass than their predecessor, resulting in a warmer overall sound. That said, their soundstage doesn't feel as immersive as the Sennheiser HD 6XX, and their treble response is more uneven than other headphones from this manufacturer, like the Sennheiser HD 650, so if you're looking for crisp vocals and instruments, you may want to check out some of Sennheiser's other headphones instead.
Check out recommendations for the best audiophile headphones, the best open-back headphones, and the best headphones for music.
Both the Sennheiser HD 660S2 and the Sennheiser HD600 are audiophile open-back headphones designed for analytical listening, though the HD 660S2 are better for this purpose. They deliver audio more consistently and have a more accurate treble response. They're soundstage also feels wider and more immersive than the HD 600's.
The Sennheiser HD 650 are slightly better audiophile headphones than the Sennheiser HD 660S2. The HD 650 are more comfortable and have a more neutral sound profile, which some users may prefer. Their passive soundstage is more immersive too. However, the HD 660S2 have more bass, which is good if you like more thumpy and rumbly genres.
The Sennheiser HD 660S2 are the next generation of the Sennheiser HD 660 S. While they have the same style, build quality, and comfort, the second generation have a warmer sound that delivers more thump and punch. Their treble range has been adjusted, although vocals and instruments are more veiled, while sibilants become a bit more aggressive due to the dip around 5kH. They also come with a dust pouch so you can store the headphones when not in use.
The Sennheiser HD 6XX are better audiophile headphones than the Sennheiser HD 660S2. While both headphones have a similar design, especially in comfort and build quality, the HD 6XX have a more neutral sound profile, which some users may prefer, and their passive soundstage is significantly more immersive. However, the HD 660S2 come with a dustbag to help protect them when not in use and an additional 4.4 mm balanced audio cable.
The HiFiMan Edition XS are better audiophile headphones than the Sennheiser HD 660S2. The HiFiMan are planar magnetic headphones that can reproduce more low-bass. Overall, they have a significantly more neutral sound profile, which some users may prefer, and are more comfortable. They have a superior passive soundstage performance and are very immersive. However, the Sennheiser are dynamic headphones and come with a dustbag to help protect them when storing them.
While the Sennheiser HD 660S2 and the Sennheiser HD 490 PRO share the same manufacturer name, the latter is a product of Sennheiser's pro audio division, which translates to a better performance for analytical listening. The HD 490 PRO are more comfortable and have a more balanced sound profile overall with their 'Producing' pads. They also have better low-frequency extension, which injects some rumble and boom into your mixes. You can even swap out their pads to change the sound profile somewhat. However, the HD 660S2 are better built and have a more detailed mid-range response. They also come with a case that can help you transport them on the go.
Test Results
The Sennheiser HD660S2 look nearly identical to the Sennheiser HD 660 S but are differentiated by the color of the manufacturer's label and nameplate on the ear cups and yokes, respectively. These headphones have bronze detailing, rather than silver, like their predecessor. That said, the frame is still largely the same, as it's made from plastic with a black satin finish, and the oval ear cups are well-padded with a microfibre cloth. Like most open-back headphones, they have a mesh grille covering their ear cups. They only come in one color variant: 'Black'.
These over-ears have a decently comfortable fit. They're similar in design to the Sennheiser HD 660 S and have the same headband design. Overall, they're lightweight, and their padding feels soft against the skin, although they're not as plush as the 'Producing' pads that come with the Sennheiser HD 490 Pro. However, they have a high clamping force out of the box, which can be uncomfortable to wear for long periods. You'll especially feel their high clamping force if you have a large, wide head or wear glasses.
These headphones aren't very portable, which is normal for audiophile headphones. They're not designed to be used on the go and can't fold into a smaller format.
Unlike the Sennheiser HD 660 S, these headphones come with a dustbag to help protect the headphones from dust accumulation when not in use. There's a drawstring to keep the pouch closed, but you can't fully seal it. Since it's made of fabric, it won't protect the headphones from water exposure or impact damage.
The build quality is good. These headphones have a similar design to the Sennheiser HD 660 S. They're partially made of plastic, with a metal driver shell and a thin metal headband that's solid and has some give for it to pivot. The ear cups are spacious, and the microfiber velour padding is plush and soft. The audio cable is also detachable. However, the point where the headband meets the yoke doesn't feel very solid, and it requires a bit of strength to adjust the headband to fit your head.
These over-ears have good stability thanks to their high clamping force. They won't move around if you're listening to audio casually at your desk or studio. However, if you like to headbang to tunes, these can move around and even fall off your head.
- Sennheiser HD 660S2 headphones
- 1/4" audio cable
- 0.17" (4.4mm) balanced audio cable
- 1/4"to 1/8" adapter
- Carrying pouch
- Manuals
The Sennheiser HD 660S2 have a warm sound profile. Although they lack low-bass, like most open-back headphones, they deliver more thump and rumble than their predecessor, the Sennheiser HD 660 S, and even have a touch more boom. They can reproduce vocals and instruments very naturally, but a dip in the low-treble veils their details and makes sibilants like cymbals sound more bright and piercing.
The frequency response consistency is excellent. Once you get a good fit, you'll achieve consistent bass and treble delivery.
The bass accuracy is very good. Although their bass response is underemphasized in the low to mid-bass, it's more neutral than the Sennheiser HD 660 S. While mixes lack thump and punch, they have a bump in their high-bass to add warmth to your mixes. The touch of extra bass doesn't overwhelm vocals and instruments, though.
The mid accuracy is outstanding. The range is very even and flat, which results in present, and natural-sounding vocals and instruments. In songs like Glassworks: I. Opening by Philip Glass, the piano sounds smooth and detailed throughout the entire track.
These headphones have satisfactory treble accuracy. The low-treble starts neutral but takes a dip that reaches its full depth in between the low to mid-treble. This roll-off can help ease the warmth of the bass range but hurts the clarity and detail of vocals and instruments. The incline in the mid-treble also ends up making sibilants like cymbals seem brighter and more piercing in comparison.
The peaks and dips performance is good. Most of the deviations are somewhat minor. The bump in the high-bass adds more warmth and boom to mixes, while another peak in the high-mid affects the right driver a little more than the left, heightening the clarity of vocals and instruments. However, a deep dip starting in the low-treble veils these sounds and is followed by a sharp peak in the mid-treble, making sibilants piercing and painful.
The Sennheiser HD 660S2's imaging performance is fantastic. Sennheiser's audiophile products usually have very consistent quality control and ergonomics, so you can expect that your unit's drivers will be well-matched. Our unit's L/R drivers are well-matched in group delay, which ensures tight bass and transparent treble reproduction. They're also well-matched in phase, amplitude, and frequency response. It's important for the accurate localization and placement of objects like voices and instruments in the stereo image. It's important to remember that imaging varies between units, though.
These headphones have a passable passive soundstage. They're open-back headphones, and like the Sennheiser HD 660 S, their soundstage seems spacious and open. However, they still struggle to produce a wide, natural, and out-of-head soundstage.
The weighted harmonic distortion performance is great. Although there's a peak in the low to mid-treble, this is hard to hear with real-life content as the affected bands are limited. As a result, audio reproduction is clean and pure, both at regular and high volumes.
These are the settings used to test these headphones. Our results are only valid when used with these settings.
The Sennheiser HD 660S2 aren't designed to block out background noise. They have an open-back design, allowing ambient sound to pass through the ear cups to create a natural and immersive soundstage. They don't block out any of the low rumble of car engines from an open window or ambient chatter. While they can partially isolate you from high-pitched noise like the hum of an AC unit, it's still minimal.
The leakage performance is bad, but this is also by design. Open-backs are meant to leak audio, as they can interact with your environment and create a more immersive passive soundstage. It isn't a problem if you're in an isolated place like a studio or room. However, if you want to use these in a noisy environment, people will hear your audio.
These headphones come with a 1/4" TRS cable and a 4.4mm balanced cable, which have the same length. They also come with a 1/4" to 1/8" adapter (0.72 ft or 0.22 m) so that you can connect it to other devices with this port.
These over-ears can connect to your PC using their audio cable with the included adapter. However, since they don't have a mic, you'll only receive audio.
You can connect these over-ears to your PlayStation console via the controller's AUX port. However, you'll need to use their adapter, and they can only receive audio.
These over-ears support audio-only when you use the adapter to connect them to your console controller's AUX port.