Sennheiser HD 660S Review – Studio Cans, Audiophile Edge

The Sennheiser 6 series of headphones has delivered some of the best headphones for mixing and mastering throughout the last few decades. The most notable is the HD 600, but the HD 650 was also superb. This review looks at the new HD 660S, which is set to replace the HD 650 in the Sennheiser lineup.

Sennheiser HD 660S

Three quarter view of the Sennheiser HD 660S headphones.

Sound

4.5/5

Comfort

4.4/5

Design

4.5/5

Durability

4.7/5

The Sennheiser HD 660S offers a dynamic sound profile with some distinctly Sennheiser characteristics. But some notable changes make it a unique offering. Below are the top-level details before we dig a little deeper.

PROS

CONS

Features

Sennheiser cans have always found a home in professional studio environments. The HD 660S looks to expand its appeal beyond just the studio. And in many aspects, Sennheiser has achieved just that but not without some compromises along the way.

Sound Quality 

The Sennheiser HD 660S has an interesting sound profile that is capable and satisfying. From a studio perspective, it gets a lot of the fundamentals right. But it also retains a fatigue-free profile, making it an appealing choice for laid-back casual listening sessions.

Let’s start with the weakest element of the sound profile. The bass response is a little underwhelming, something that is not uncommon with open-back headphones but noticeably lackluster here. It does deliver a high degree of accuracy and decent kick but struggles in the sub-bass regions. Not a great pair of cans if you are a bass head.

The midrange, however, is sublime and a hallmark of many Sennheiser headphones. Rich and detailed, with an excellent dynamic representation of the source material. Accuracy is very high, making it a breeze to make accurate mixing decisions. There is a healthy dose of warmth for casual listening without introducing color.

The top end is tough to judge and will come down to personal preference. It is noticeably subdued compared to other studio-focused headphones, which are often overly bright. For casual listening, this is fantastic as you can comfortably listen to these for hours without fatigue. This fatigue-free experience is also ideal for long sessions in the studio. But it does lack the accuracy that some may desire.

Specification-wise, the HD660S offers a broad 9Hz-41.5kHz frequency range with a 104dB SPL. Accuracy is high across the range except for the noticeable drop-off in the lows and slight suppression in the highs. The relatively high SPL also offers a decent amount of headroom.

Sennheiser HD 660S Specifications.

The HD 660S provides a broad range with a good level of accuracy.

Total harmonic distortion is ultra-low at under 0.04%, and the imaging across the two drivers is precise. Sennheiser knows how to manufacture excellent cans; these headphones are a perfect example of that skill.

Where the HD 660S does fall short is in its sound stage. Open-backed headphones are the go-to recommendation if you want a more speaker-like experience, but these don’t really offer that. Far roomier than closed-back cans but not as spacious as other options.

When considering everything, the HD 660S is another highly capable entry into the Sennheiser stable. The sound profile is pleasant, albeit not as accurate as some may want or need, but It does achieve its goal of broadening its appeal. These are an enticing choice if you need an all-rounder set of cans that can pull double duty.

Comfort 

The Sennheiser HD 660S also offers a comfortable fit which ties in nicely with its fatigue-free sound profile, but it isn’t perfect.

The large oval earcups will appeal to people with more prominent ears. Far more space than comparable cans with round ear cups. The ear padding is also fantastic, and the thick padding with velour covering delivers a high level of comfort with just enough swivel to adapt to your head shape.

The headband also features a substantial amount of padding with an indent to prevent a pressure point from forming at the top of your head. The headband also adjusts with satisfying clicks between levels.

Front view of the Sennheiser HD 660S headphones.

Thick padding throughout provides lots of cushioning.

My only issue with the comfort level is the strong clamping force. For a pair of headphones intended for long sessions, the grip could have been a bit looser. I appreciate the tighter grip’s stability, but the clamping force might be too much for your liking if you have a larger-than-average head.

Due to the open-back design, there is ample opportunity for air to pass through. This ensures your ears won’t get too hot even with the firm grip these have on your head.

These are also lightweight at 0.57 lbs. (260 grams) thanks to a predominantly plastic build. It will be a welcome change if you come from bulky audiophile-focused cans, even more so if you use planar-magnetic headphones.

Despite the slightly firm hold, the experience is still exceptional. These are comfortable headphones that, for most, will be perfect for long listening sessions, whether that is in the studio or when you are sitting on the couch.

Design 

Studio headphones don’t need to win any beauty awards, but it is always nice to be able to look at a pair of cans and appreciate their aesthetic. The HD 660S doesn’t stray far from the existing design mentality of Sennheiser cans, but a few minimal tweaks do elevate it and bring these into the modern era.

The all-black plastic design ensures a sleek and professional appearance. Accents are minimal, with restrained use of the Sennheiser logo and name. I especially appreciate that the name doesn’t run across the entire length of the headband. The updated grille design adds a little character with more contours than other Sennheiser cans.

For some, these might come across as a little bland, but for my taste, these are precisely what I look for in a professional set of studio headphones.

Close up photo of the Sennheiser HD 660S.

Simple yet striking design.

Some other design decisions are worth highlighting. These headphones are clearly intended for use at home or in the studio. They do not collapse, and you don’t get access to a pouch unless you want to buy one separately.

The open-back design does, of course, leak sound and doesn’t provide any isolation. You should explore a closed-back option if you need either of these features.

The included cables feature a Y design with the standard Sennheiser connecting pins. I don’t mind this design, but it does make connecting to the correct side trickier in low-light situations. The cables are long and straight, and an adapter cable is provided. You won’t have any issues connecting these headphones to various devices.

At 150 ohms, these work best with a good headphone amp, but even a direct connection to lower-powered devices didn’t yield a massive drop in quality. Versatile enough to be a viable option for all your listening needs.

Durability 

The Sennheiser HD 660S also maintains the high build quality I’ve come to expect from Sennheiser products. Despite the all-plastic build, these are surprisingly robust and durable. But when I factor in the price point, I wouldn’t expect anything less.

Don’t get me wrong; these are not built like a tank. Certainly not capable of handling any extreme stress, but in a studio environment, you’ll unlikely run into any issues. Take due care, and these headphones will last you a long time.

Sennheiser HD 660S Details.

The HD 660S is a well-constructed pair of headphones.

The headband is sturdy, and the ear cup padding is durable and replaceable. The detachable cables are also replaceable, and while I’m not a massive fan of the pin system, I’ve never had any problems with it. I just prefer a more classic connection and a bayonet-style locking mechanism, but these are still fantastic.

The 42mm transducers are finely tuned and precision engineered. Once again highlighting the decades of experience that Sennheiser has up its sleeve. The grille covering the drivers is also solid and scratch resistant.

Value 

I’m a little miffed when it comes to the value proposition of the HD 660S. In one regard, these are competent headphones with a sound profile many will enjoy. But the strange hybrid of trying to appeal to both audiophiles and professionals does muddy the waters.

Compared to high-end audiophile headphones, these offer excellent value, but they don’t reach the heights that those headphones provide. Line these up against dedicated studio headphones, and you might be better off exploring other options with more detail and a lower price point.

It’s a little bit of a jack of all trades but a master of none result. As an all-rounder, it does present good value, but if you need it for a specific task, there are more appealing options out there.

Quick Guide To Headphone Terminology

If you’ve spent any amount of time looking at reviews for headphones, you’ll have come across some terms you may not recognize. Below are a few key pieces of terminology and what they mean.

Impedance – This measures how much resistance the headphones offer against an electrical current. The higher the number, the worse the performance will be with battery-powered devices like laptops and smartphones.

Transducer – This is the driver within each earcup. They are made of multiple components with the sole task of transforming a digital signal into sound waves.

Close up photo of the Sennheiser HD 660S.

You can clearly see the transducers in open-back headphones.


THD – This stands for Total Harmonic Distortion and measures the amount of distortion present across the frequency response. Good headphones will have a low level of distortion with a rating below 0.05%.

Soundstage – This represents how the headphones place audio within the stereo field. Good headphones will create the feeling of listening to loudspeakers, where you can distinguish where the sound is coming from, whether in the front, sides or behind you. It can also give you a feeling of space when listening to audio. 

Other Options

There are several fantastic open-back headphones available. Below we take a quick look at some alternatives that are worth considering.

Shure SRH1840 Review

The SRH1840 is a premium pair of open-back headphones from Shure. It features a slick design and superb sound quality

  • Clear and precise audio with a richer soundstage compared to the HD 660S.
  • Durable construction and replaceable components.
  • Much like the HD 660S, these are not cheap headphones.
Three quarter view of the Shure SRH1840 headphones.

Shure SRH1840

4.7/5

Audio-Technica ATH-R70x Review

If you don’t want to spend as much, the ATH-R70x from Audio-Technica is an appealing choice. It also features some unique elements that set it apart from the competition. 

  • Rich and detailed sound profile that offers high accuracy and neutrality.
  • The unique “3D Wing Support” system delivers a very high level of comfort.
  • At 470 ohms, these are not a good choice for lower-powered devices like laptops.
Three quarter view of the Audio-Technica ATH-R70x headphones.

Audio-Technica ATH-R70x

4.7/5

AKG K701 Review

For those that want a dedicated pair of reference-grade headphones, the K701 from AKG should be on your list of options. They are an excellent pair for serious professionals.

  • A very accurate response across the entire frequency range.
  • Striking design and superb comfort level.
  • Doesn’t feature a detachable cable like the HD 660S.
Three quarter view of the AKG K701 headphones.

AKG K701

4.6/5

Should You Buy?

The HD 660S is another superb addition to Sennheiser’s catalog of headphones. This new attempt at capturing the audiophile market is a smart business move, and to be fair, the sound profile will please many. For extreme purists, there are faults to be found but not enough to make it a dealbreaker.

With solid construction, good comfort, and replaceable components, these can assimilate into a variety of situations. A viable option for mixing and mastering while retaining enough character to make it an appealing choice for casual listening. While I might miss the HD 650 this is replacing, I’m glad to see that Sennheiser still has what it takes to deliver an exceptional pair of cans.

Three quarter view of the Sennheiser HD 660S headphones.

Sennheiser HD 660S

4.6/5

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Patryk Biernacki

Patryk Biernacki

For over 20 years I've been involved in the world of DJing. Now I want to share my experience so that DJing is more accessible for anyone with a passion for music.

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