Sennheiser HD 660S2 Review: Is it Truly an Upgrade?

Sennheiser is a brand that has achieved legendary status with headphones like the well-known HD 580, HD 600, HD 650, and HD 800. They have recently released a brand new over-ear open-back headphone, the HD 660S2. Today I will be talking about the latest addition to the Sennheiser 600 series headphones—the HD 660S2. This headphone is not only the newest in the lineup but also the most expensive, which raises a lot of questions. Is it a good headphone in general? And is it worth the higher price tag? So Let’s find out if it lives up to their reputation.

Overview of the Sennheiser HD 660S2

Sennheiser HD 660S2

The HD 660S2 follows the classic design of Sennheiser’s HD 600 series. The ear cup shape and the open-back grille remain the same. The headband design also retains the familiar clicky adjustment mechanism. It’s worth noting that these headphones are highly open, almost like wearing speakers on your head. So, if you use them anywhere other than in your bedroom or studio, be prepared to share the sound with those around you. The adjustment mechanism is quite solid, with ample length adjustment. However, depending on your head shape, you might find them slightly clampy. The clamp force is relatively strong, although it tends to adjust over time. I personally own a pair of HD 650s, and they have become more comfortable to wear over time. But initially, they can feel a bit uncomfortable, especially for people with larger heads.

In terms of build quality, the headphones are what you would expect. They feature a combination of plastic and metal, giving them a solid and sturdy feel. The velour ear pads, which are common in the HD 660 series, provide good comfort for extended listening sessions. They are also more resistant to sweat and don’t deteriorate over time like many faux leather pads.

Exceptional sound quality.Higher price range.
Comfortable fit.Non-foldable design.
Durable build quality.Limited isolation.
Wide soundstage for immersive listening experience.
Detachable cable for convenience and versatility.

Key Features and Specifications

Sound ModeStereo
Connection TypeWired
Headphone FitOver-the-Ear
Adjustable HeadbandNo
Transducer principledynamic, open
Transducer size38 mm
Frequency response8 – 41,500 Hz
Impedance300 Ω
Sound pressure level (SPL)104 dB (1 kHz, 1 Vrms)
Total harmonic distortion (THD)<0.04% (1 kHz, 100 dB)
Ear couplingOver-Ear
Adapter6.3 mm (1⁄4 inch) to 3.5 mm
Connector6.3 mm (1⁄4 inch) jack plug, 4.4 mm balanced plug
Cable length1.8m
Country of originIreland
Magnetic field4.5mT

Design and Build Quality

There haven’t been many changes visually. The headphones feature a black plastic build with metal grids on the sides since they are open-back headphones. They are engineered in Germany and produced in Ireland, ensuring high build quality despite the plastic construction. The new bronze colorway for the lettering and logo adds a touch of elegance, and the overall design looks simple and classy. The weight of the headphones is 260 grams, which makes them lightweight and comfortable for extended listening sessions.

One issue I encountered with these headphones is that they are slightly tight on the head, which can cause some discomfort. However, the plush earpads are excellent and provide a comfortable fit. The cushioning on the headband is also comfortable, although it consists of two separate pieces for unknown reasons.

One thing worth mentioning is the packaging. The new box feels like a downgrade compared to the previous foam storage case, which many people used to store their headphones. It’s a minor gripe, but it can be seen as a letdown for loyal customers who expected more.

Design and Build Quality

Sound Quality

Sound quality is a subjective aspect of any headphone review. Personal preferences for sound vary greatly among individuals. Personally, I prefer headphones with a brighter sound and a bit more bass, but others may prefer warmer or richer sound. In short, it is a mostly pleasant sounding headphone with some unique characteristics. The HD 660S2 is said to have better sub-bass extension compared to its predecessor, which is an appealing feature. However, it doesn’t provide the full bass extension that many audiophiles desire. The difference in sub-bass extension is subtle and might not be a significant selling point for those seeking more bass.

The more perceptually relevant aspect of the HD 660S2 is its tuning in the upper mids and lower treble. It has a dip around 3kHz and a relaxed presentation in that region, which might affect the clarity and instrument tones. While this tuning might work well for certain styles of music like heavy metal or rock, it might not be preferred by those who appreciate clarity and a more neutral sound. Compared to the HD 600 and HD 650, the HD 660S2 sounds a bit thicker throughout the mids.

In terms of soundstage and imaging, the HD 660S2 performs well. Instruments and vocals are well-positioned, and there is a good sense of depth. However, there are better headphones in terms of imaging available.

Sound Quality


Performance and Technical Features

When it comes to treble performance, the HD 660S2 performs solidly, but it’s worth noting that this series is known for having less treble as the pads wear in over time. EQ adjustments can be made to improve the sound quality, and there are recommended EQ settings available for those interested.

Subjectively, the HD 660S2 is similarly detailed and resolving as the HD 650 and HD 600. It excels in instrument separation and incisiveness, allowing you to isolate individual instrument lines easily. However, it doesn’t provide the same sense of physicality and impact as some other headphone models.

Sound Quality

User Experience

Sennheiser has updated the cables for the HD 660S2. The new version comes with a 4.4mm and a 6.3mm cable. The cable length is around six feet, which should be sufficient for most people’s needs. The previous version had a 10-foot cable, so the newer cable is more manageable for most users. However, some individuals may still prefer the longer cable, and it’s possible to obtain one second-hand or order it directly from Sennheiser.

User Experience

Comparisons (HD 660S2 vs HD 660S vs iBasso SR3)

HD 660S2 vs HD 660S vs iBasso SR3

In our comparison, we brought in the Sennheiser HD 660S, the previous revision, as well as the iBasso SR3. The differences between the HD 660S and the HD 660S2 are minimal. The main change is the bronze-colored writing on the HD 660S2, along with a slightly smaller Sennheiser logo. Other than that, the padding, design, frame, adjustments, and ear pads remain almost identical.

On the other hand, the iBasso SR3 is a completely different headphone. It features a wire frame with leather-padded adjustments and large, cushy, vented leather pads. The frame is predominantly metal, giving it a perceived higher build quality compared to the Sennheiser headphones. However, it’s difficult to say how well the hinges and other components will hold up over time. The iBasso SR3 provides a softer, cushier feel on the head, making it more comfortable for many people. Overall, the SR3 may be considered better built, but personal preferences for comfort may still vary.

When comparing the HD 660S2 and the HD 660S, the improved bass extension and slightly increased bass quantity in the S2 become more apparent. This enhancement elevates the overall sound quality and naturalness, making the HD 660S sound comparatively thin without the extended low-end support.

The comparison with the iBasso SR3 reveals a different tuning philosophy. While the HD 660S2 leans towards accuracy and reveals more detail, the SR3 offers a more relaxed and fun sound signature. The SR3 has solid bass extension and a slight emphasis in the mid-bass, providing more punch. In terms of treble, the HD 660S2 has better extension, while the SR3 pulls back the upper mids and rolls off the top end slightly, resulting in a less fatiguing sound.

The soundstage of the SR3 is wider, although the imaging may not feel as weighty or holographic as that of the HD 660S2. Ultimately, the choice between the two headphones depends on personal preferences, with the HD 660S2 offering a more engaging and revealing sound, while the SR3 provides a more relaxed and potentially fun experience.

Final thoughts on the Sennheiser HD 660S2

Recommending this headphone is a bit complicated for me. It’s undoubtedly a good headphone, but the 600 series already has exceptional models that make the HD 660S2 feel like a modest upgrade rather than a significant jump in quality. The Sennheiser HD 660S2 headphones are excellent for those who prefer a warmer sound, with a focus on bass and smooth highs. They are also great for watching movies due to their immersive soundstage. The price for these headphones is $500+, and whether it’s worth it or not is subjective. I’ve provided all the details based on my listening experience and the information provided by Sennheiser.

James Smith has always been intrigued by electronic products since his childhood. After his post graduation in electronics from a popular university, he decided to pursue a career in the electronics sector. But his calling for writing about these marvellous pieces of work got the better of him. That is how UBG was started. With a writing career spanning more than 12 years, James has worked on several hundred product reviews. During his free time, he like to spend time with his pet dog and relax in the swimming pool.