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Sennheiser HD 660S2 Headphones Review

Tested using Methodology v1.5
Reviewed Mar 08, 2023 at 08:41 am
Sennheiser HD 660S2 Picture
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

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

7.9 Neutral Sound

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.

Pros
  • Consistent audio delivery.
  • Well-built and decently comfortable fit.
Cons
  • Mediocre passive soundstage.
3.6 Commute/Travel

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.

Pros
  • Well-built and decently comfortable fit.
Cons
  • Aren't designed to block out background noise.
  • Leak a lot of audio.
  • Bulky and wired design can get easily snagged on something.
5.4 Sports/Fitness

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.

Pros
  • Well-built and decently comfortable fit.
Cons
  • Can move around or fall off with large head movements.
  • Bulky and wired design can get easily snagged on something.
4.2 Office

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.

Pros
  • Well-built and decently comfortable fit.
Cons
  • Aren't designed to block out background noise.
  • Leak a lot of audio.
4.3 Wireless Gaming

The Sennheiser HD 660S2 are wired headphones, and you can't use them wirelessly.

6.4 Wired Gaming

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.

Pros
  • Well-built and decently comfortable fit.
Cons
  • Mediocre passive soundstage.
1.5 Phone Calls

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
  1. Updated Mar 08, 2023: Review published.
  2. Updated Mar 02, 2023: Early access published.

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.

Sennheiser HD 660 S

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.

Sennheiser HD 650

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.

Sennheiser HD 6XX

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.

HiFiMan Edition XS

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.

Test Results

perceptual testing image
Design
Design
Style
Type Over-ear
Enclosure Open-Back
Wireless No
Transducer Dynamic

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'.

7.0
Design
Comfort
Weight 0.57 lbs
Clamping Force
1.5 lbs

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. However, they have a high clamping force out of the box, which can be uncomfortable to wear for long periods. If you have a large, wide head or wear glasses, you'll especially feel their high clamping force.

0
Design
Controls
OS Compatibility
No Controls
Ease Of Use No Controls
Feedback No Controls
Call/Music Control No
Volume Control No
Microphone Control No
Channel Mixing
No
Noise Cancelling Control No
Talk-Through
No
Additional Controls No
5.4
Design
Portability
L 7.7" (19.6 cm)
W 7.1" (18.0 cm)
H 3.5" (9.0 cm)
Volume 193.84 in³ (3,176.40 cm³)
Transmitter Required No

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.

6.5
Design
Case
Type Pouch
L N/A
W N/A
H N/A
Volume N/A

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.

7.5
Design
Build Quality

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.

7.5
Design
Stability

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.

Design
Headshots 1
Design
Headshots 2
Design
Top
Design
In The Box

  • Sennheiser HD 660S2 headphones
  • 1/4" audio cable
  • 0.17" (4.4mm) balanced audio cable
  • 1/4"to 1/8" adapter
  • Carrying pouch
  • Manuals

Sound
Sound
Sound Profile
Bass Amount
-3.07 dB
Treble Amount
-2.12 dB

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.

8.7
Sound
Frequency Response Consistency
Avg. Std. Deviation
0.27 dB

The frequency response consistency is excellent. Once you get a good fit, you'll achieve consistent bass and treble delivery.

Sound
Raw Frequency Response
7.7
Sound
Bass Accuracy
Std. Err.
3.04 dB
Low-Frequency Extension
58.23 Hz
Low-Bass
-5.71 dB
Mid-Bass
-1.62 dB
High-Bass
1.82 dB

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.

9.2
Sound
Mid Accuracy
Std. Err.
1.01 dB
Low-Mid
1.19 dB
Mid-Mid
0.08 dB
High-Mid
0.56 dB

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.

7.1
Sound
Treble Accuracy
Std. Err.
4.25 dB
Low-Treble
-3.05 dB
Mid-Treble
-0.5 dB
High-Treble
-6.4 dB

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.

7.6
Sound
Peaks/Dips
Peaks
1.51 dB
Dips
1.37 dB

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.

9.0
Sound
Imaging
Weighted Group Delay
0.13
Weighted Phase Mismatch
1.98
Weighted Amplitude Mismatch
0.6
Weighted Frequency Mismatch
1.44

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.

6.2
Sound
Passive Soundstage
PRTF Accuracy (Std. Dev.)
4.33 dB
PRTF Size (Avg.)
1.79 dB
PRTF Distance
3.09 dB
Openness
9.5
Acoustic Space Excitation
8.5

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.

0
Sound
Virtual Soundstage
Head Modeling
No
Speaker Modeling
No
Room Ambience
No
Head Tracking
No
Virtual Surround
No App
8.1
Sound
Weighted Harmonic Distortion
WHD @ 90
0.239
WHD @ 100
0.089

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.

Sound
Test Settings
Firmware
No Firmware
Power
Passive
Connection
Wired
Codec
PCM, 24-bit, 48kHz
EQ
No EQ
ANC
No ANC
Tip/Pad
Default
Microphone
No Microphone

These are the settings used to test these headphones. Our results are only valid when used with these settings.

Isolation
1.3
Isolation
Noise Isolation
Isolation Audio
Overall Attenuation
-3.73 dB
Noise Cancelling No
Bass
0.02 dB
Mid
0.12 dB
Treble
-11.14 dB

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.

1.8
Isolation
Leakage
Leakage Audio
Overall Leakage @ 1ft
62.8 dB

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.

Microphone
Microphone
Microphone Style
Integrated
No
In-Line
No
Boom
No
Detachable Boom
No
Mic No
0
Microphone
Recording Quality
Recorded Speech
N/A
LFE
N/A
FR Std. Dev.
N/A
HFE
N/A
Weighted THD
N/A
Gain
N/A
0
Microphone
Noise Handling
SpNR
N/A
Noise Gate
No
Speech + Pink Noise Handling
N/A
Speech + Pink Noise Audio Sample N/A
Speech + Subway Noise Handling
N/A
Speech + Subway Noise Audio Sample N/A
Active Features
0
Active Features
Battery
Battery Type
No Battery
Continuous Battery Life
N/A
Additional Charges
N/A
Total Battery Life
N/A
Charge Time
N/A
Power-Saving Feature
No
Audio While Charging
No
Passive Playback
Passive Headphone
Charging Port None
0
Active Features
App Support
App Name No App
iOS No
Android No
macOS No
Windows No
Equalizer
No
ANC Control
No
Mic Control No
Room Effects
No
Playback Control
No
Button Mapping No
Surround Support
No
Connectivity
0
Connectivity
Bluetooth
Bluetooth Version
No Bluetooth
Multi-Device Pairing
No
NFC Pairing
No
Line Of Sight Range
N/A
PC Latency (SBC)
N/A
PC Latency (aptX)
N/A
PC Latency (aptX HD)
N/A
PC Latency (aptX-LL)
N/A
iOS Latency
N/A
Android Latency
N/A
0
Connectivity
Non-Bluetooth Wireless
Non-BT Line Of Sight Range
N/A
Non-BT Latency
N/A
9.5
Connectivity
Wired
Analog Audio
Yes
USB Audio
No
Detachable Yes
Length 5.91 ft (1.80 m)
Connection
1/4" TRS
Analog/USB Audio Latency
0 ms

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.

Connectivity
PC Compatibility
Analog
Audio Only
Wired USB
No
Non-BT Wireless
No

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.

Connectivity
PlayStation Compatibility
PS4 Analog
Audio Only
PS4 Wired USB
No
PS4 Non-BT Wireless
No
PS5 Analog
Audio Only
PS5 Wired USB
No
PS5 Non-BT Wireless
No

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.

Connectivity
Xbox Compatibility
Xbox One Analog
Audio Only
Xbox One Wired USB
No
Xbox One Non-BT Wireless
No
Xbox Series X|S Analog
Audio Only
Xbox Series X|S Wired USB
No
Xbox Series X|S Non-BT Wireless
No

These over-ears support audio-only when you use the adapter to connect them to your console controller's AUX port.

0
Connectivity
Base/Dock
Type
No Base/Dock
USB Input
No
Line In
No
Line Out
No
Optical Input
No
RCA Input
No
Dock Charging
No
Power Supply
No Base/Dock

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