Sennheiser HD-660S2 review: neutral and detailed sound that's best for the studio

Open-back Sennheiser headphones that are gentle on the ears

The Sennheiser HD-660S2 over-ear headphones hanging on a hook near a window
(Image: © Future/TechRadar/Henry St Leger)

TechRadar Verdict

The Sennheiser HD-660S2 headphones are a great purchase for anyone wanting to dip their toes into open-backed audio, with a gently expansive soundstage that doesn’t block out the outside world. The neutral audio signature here is effective, inoffensive, and it’s clear that the HD-660S2 headphones improve on their predecessors and are a great entry point into the delights of open-backed cans.

Pros

  • +

    Open-back design and comfortable fit

  • +

    Consistent, neutral sound

  • +

    Various cable options

Cons

  • -

    Lack of smart features

  • -

    Needs a separate amp to get the most out of them

Why you can trust TechRadar We spend hours testing every product or service we review, so you can be sure you’re buying the best. Find out more about how we test.

Sennheiser HD-660S2: Two-minute review

The Sennheiser HD-660S2 headphones are the latest in Sennheiser’s series of open-backed models, offering a premium audio experience, comfortable fit and general sense of superiority over regular commercial cans.

These are wired headphones made for the mixing booth, with brilliant sound recreation, plush cushioning, and the rigid headband needed to prevent vibration while you listen to your favorite tracks. While cans like these are usually designed with professional use in mind – sound mixing and mastering – the HD-660S2s are also great for all-round music listening, with a relaxed sound signature and a boosted bass response compared to the original HD-660S.

You won’t be able to use these headphones on the subway, mind – as an open-backed model, there’s little-to-no sound isolation here and thus, they will only really suit those who listen to audio while chained to their desk (or lounging in a comfy listening chair). 

Unlike many of the best over-ear headphones we've tested, there's no Bluetooth or alternative wireless connectivity other than a detachable cable here. Ultimately, the HD-660S2 are best for static listening, sound mixing, or nursing a favorite album in high quality sound in your own home (without fear that you’ll miss the ring of a doorbell). There isn’t a huge amount of sound leakage, though, so you should be able to sit near someone without blaring Taylor Swift in an obnoxious manner.

The Sennheiser HD-660S2 headhphones pictured on a wooden surface.

Sennheiser’s headphones are a delight to wear, with thick, plush foam. (Image credit: Future/TechRadar/Henry St Leger)

High impedance headphones like these are able to limit sound distortion, thanks to a thin and sensitive voice coil, ensuring accurate sound and improved bass reproduction – and at 300 Ohms impedance, the HD-660S2 are hard to beat on this metric.

It’s worth noting that you won’t always get the full experience using everyday source devices such as your phone or laptop though; while the 2023 Macbook Air packs in support for high-impedance headphones, this isn’t common across the board, and the HD-660S2 headphones are best enjoyed for those working with high-quality audio files and devices – as well as one of the best DACs (which often double as amplifiers for these kinds of harder-to-drive cans). Thankfully, a variety of connection cables (6.3mm and 4.4mm, with a 3.5mm adapter for more pedestrian uses) ensure you can connect these cans to whatever source devices you have.

Sennheiser’s headphones are a delight to wear, with thick, plush foam and an open soundstage that surrounds the ears rather than funneling directly into them. They’re easy enough to wear for long listening periods, though an intentionally rigid construction means they can feel a little heavier than their listed 260g specification would usually suggest. While the cans come with a soft carry pouch, you won’t be able to pivot the earcups or decrease the amount of space they take up.

The Sennheiser HD-660S2 over-ear headphones in a small bag.

These headphones do come with a soft carry pouch, but you won’t be able to pivot the cups, which makes them tricky to carry. (Image credit: Future/TechRadar/Henry St Leger)

Even with standard music streaming over Spotify, it’s a pleasant and rewarding experience, hearing the soft croons of Lorde on Buzzcut Season dip in and out as a gentle bass track seems to float in the air around your ears. The open soundstage brings out the depth and complex layers of Ethel Cain’s Crush, as voice, synth and instrumentals are expanded out of the song’s hazy, dreamlike sound. Meanwhile, over in Beyonce’s ALIEN SUPERSTAR, the HD-660S2’s drivers can capably draw out bass detail in a way lesser headphones would simply miss entirely.

Those used to the immediate impact and power of quality closed-backed headphones may miss it, but there’s no doubt that the HD-660S2's output is easy on the ears, with a cohesive effect across frequencies high and low.

Open-backed headphones aren’t for everyone, and those of you wanting cans that work on the go, or pack in the usual medley of smart features (Bluetooth, ANC, transparency mode, voice assistants, etc) will want to look elsewhere. But for the discerning or professional listener, the Sennheiser HD-660S2 headphones hit different.

A close-up of the Sennheiser HD-660S2 headphones against a wooden surface.

There’s little-to-no sound isolation here, so don't take these headphones with you on your commute. (Image credit: Future/TechRadar/Henry St Leger)

Sennheiser HD-660S2 review: Price & release date

  • They cost $599 / £499 / AU$949
  • Launched in March 2023

The Sennheiser HD-660S2 headphones retail for $599 / £499 / AU$949, and are available globally. Check out the Sennheiser promo codes currently available to see how you could save more. Its retail price is in line with the similarly-specified Beyerdynamic DT 1990 PRO, though only a third of the price of the premium Sennheiser HD 800 S, so there’s still a lot more out there for those wanting top-line audiophile cans.

You can also get the original Sennheiser HD-660S for a little cheaper, though the newer model boasts a more fleshed-out bass response. And let's not forget, if it's a cheap open-back design you want, Grado's affordable SR80x started at just $125 / £130 / AU$179 but may even be a little cheaper now… 

Sennheiser HD-660S2 review: Specs

Swipe to scroll horizontally
Drivers38mm
Active noise cancellationNo
Impedance300 Ohms
Weight260g
ConnectivityWired (6.3mm, 4.4mm, 3.5mm)
Frequency range8Hz-41,500Hz

Should I buy the Sennheiser HD-660S2?

Buy them if...

You need professional sound mixing headphones
Open-backed headphones are exceptional for accurate sound recreation, making these a great choice for those dealing with audio on a professional basis.

You want detailed bass
The improved bass response over the HD-660s means that lows are brilliantly and accurately realized – if you’re used to regular commercial cans, you should hear details you’ve never noticed before.

You listen to a variety of music
Sennheiser’s characteristically relaxed, neutral sound signature is a delight for pretty much any genre of music you could think of, and great for all-round usage. 

Don't buy them if...

You need commuter headphones
As flashy as the HD-660S2s are, you don’t want to flash them on public transport. The open-backed design means there’s a little sound leakage, and no real isolation from environmental noise.

You want the latest smart features
You won’t get Bluetooth connectivity, voice assistants, or active noise cancelling here – so I wouldn’t recommend these cans for those after a smart experience over a high-fidelity one.

You’re not using high-impedance sources
If your source devices can’t make the most of these high-impedance headphones, then the 300 Ohms count on these headphones aren’t fully utilized. Keep in mind that the cheaper HD-660S model only packs in 150 Ohms, but is about 10-20% cheaper.

Sennheiser HD-660S2 review: Also consider

Swipe to scroll horizontally
Beyerdynamic DT 1990 ProSennheiser HD 800 SSennheiser HD-660S
Price£479£1,499£429
Drivers45mm56mm42mm
Active noise cancellationNoNoNo
Impedance250 Ohms300 Ohms150 Ohms
Weight370g330g260g
ConnectivityWired (3.5mm)Wired (6.35mm, 4.4mm)Wired (6.35mm, 4.4mm)
Frequency range5-40,000Hz4-51,000Hz9-41,500Hz
Image

Beyerdynamic DT 1990 Pro
These open-back rivals offer stunning resolution, soundstage and build quality. You'll need to pay a little more, but they're great value for money and ideal for audiophiles. Read our full <a href="https://www.techradar.com/reviews/beyerdynamic-dt-1990-pro" data-link-merchant="techradar.com"">Beyerdynamic DT 1990 Pro review.

Image

Sennheiser HD 800 S
A step up from the Sennheiser HD-660S I'm reviewing here, the Sennheiser HD 800 S are similar in both features and style, boasting an open-back design. They're almost three times the price because they have 56mm ring radiator transducers built-in, some of the largest you'll find.

How I tested the Sennseiser HD-660S2

A member of the TechRadar team wearing the Sennheiser HD-660S2 headphones in front of a wooden door.

I mostly tested the Sennheiser HD-660S2 headphones at home, using Spotify, YouTube and Twitch videos and even my Nintendo Switch to test a variety of sources. (Image credit: Future/TechRadar/Henry St Leger)
  • Tested for one week in a home office
  • Primarily tested with Spotify desktop app on Macbook

To test the Sennseiser HD-660S2, I hooked them up to the headphone jack in my Macbook Air. Given these aren’t closed-back commuter headphones, or Bluetooth compatible, there wasn’t much point in taking them on public transport.

I focused testing on static use, both for background music and focused on listening in the home. Most testing was done through Spotify, where I broadly keep my music catalog, though I also used the HD-660S2 to listen to podcasts and YouTube/Twitch videos, to cover a variety of sources. I also gave them a spin with my Nintendo Switch, and they were certainly effective at drawing out bass detail on game soundtracks, if a little wasted on an everyday gaming device.

As the former Home Cinema Editor for TechRadar, I have years of experience testing and evaluating the quality of audio devices, from headphones and soundbars to Bluetooth speakers.

  • First reviewed: March 2023
Henry St Leger

Henry is a freelance technology journalist, and former News & Features Editor for TechRadar, where he specialized in home entertainment gadgets such as TVs, projectors, soundbars, and smart speakers. Other bylines include Edge, T3, iMore, GamesRadar, NBC News, Healthline, and The Times.