Sennheiser headphones have been around forever, yet they keep coming up with new gear at a variety of prices. Now there’s a new headphone that’s an obvious successor to their classic HD 600 headphones, and a few newer iterations that have come along.

Sennheiser HD 660S2 Headphones

Is the HD 660S2 a headphone that will carry the torch to new heights, or just a slight evolution to a highly respected brand?

Highlights

Sennheiser HD 660S2 Headphones Highlights

  • Good build quality.
  • 300-ohm impedance which should easily pair to most high-quality source components.
  • Comfortable, replaceable ear cushions.
  • 6.3 mm plug with 3.55 mm adapter.
  • Replaceable cables – not hard-wired.
  • Travel carry pouch.
  • Left and right earpieces not plainly marked.

The Sennheiser HD 660S2 is a quality, well-built headphone. It looks physically similar to the headphones that preceded it at a similar price level. The company claims it offers extended deep bass, a warm sound, and it continues Sennheiser’s tradition of comfortable, open-back headphones.

Sennheiser HD 660S2 Headphones Mood Shot

My listening tests confirm the Sennheiser claims for this headphone. It offers clear high frequencies, deep bass (more than I’ve heard from any Sennheiser headphone), and comfort typical of open-back designs. It’s a no-frills headphone. No Bluetooth is on board, meaning no wireless operation.

It’s generally a neutral transducer, with a little bit of high-frequency roll-off to keep it from shrieking, which I expect from a quality set of headphones. At $599.95 it represents good value in comparison to its competitors.

Introduction

I have a long love affair with Sennheiser headphones. I was introduced to them way back in my college days when the Sennheiser HD 414 headphones were standard equipment for announcers when I worked at a commercial classical FM station. They were comfortable and sounded great on some challenging music. They weren’t expensive (I think around $20 back then) and I, and many of the other staffers bought pairs to use at home to listen on whatever little stereo systems we had in our dorm rooms. I think I had a small Pioneer receiver, and AR 4X speakers, but I couldn’t crank them up without risking violence from my dorm mates, so headphones were a great option. The HD 414s were the first open-back on-ear headphones I had ever experienced, so they were very comfortable, and I could wear them while studying.

Over the many years since then, I continued to buy Sennheiser headphones, and still listen to my HD 600 headphones, which are still on sale 20 years after their initial release. Somewhere I also have a pair of HD580 headphones, which were the direct predecessor to the 600s.

Sennheiser is still a family-owned business, and it’s been serving customers for 3 generations. Their headquarters are in Wedemark near Hanover, Germany, with many of their headphones built in Ireland.

The consumer business of Sennheiser has been acquired by Sonova in March 2022. Sonova is a leading manufacturer of hearing aids and aims to expand into the consumer space with the Sennheiser brand and its deep technical expertise. The three product categories Premium headphones (Momentum), Audiophile (wired high-end headphones & soundbars), and Hearing (hearing assistance devices) will be the main focus going forward, with the same development and product teams as before.

Sennheiser HD 660S2 Headphones Specifications
Transducer principle:

Dynamic, open

TTransducer size:

38 mm

Frequency response:

8 – 41,500 Hz

Impedance:

300 Ω

Sound pressure level (SPL):

104 dB (1 kHz, 1 Vrms)

Total harmonic distortion (THD):

<0.04% (1 kHz, 100 dB)

Ear coupling:

Over-Ear

Weight:

260g

Adapter:

6.3 mm (1⁄4 inch) to 3.5 mm

Connector:

6.3 mm (1⁄4 inch) jack plug, 4.4 mm balanced plug

Cable length:

1.8m

Country of origin:

Ireland

Magnetic field:

4.5mT

Included:

HD 660S2 headphones
6.3 mm cable (1.8 m), 4.4 mm balanced cable (1.8 m)
6.3mm to 3.5mm adapter
Carry pouch

MSRP:

$599.95

Company:

Sennheiser

SECRETS Tags:

Sennheiser, HD660S2 headphones, over-ear, audiophile headphones

Design

Sennheiser says it designed these headphones for a ‘relaxed’ sound and that’s a fair description of what you will get. The HD 660S2 headphones have a lot of DNA from earlier Sennheiser products.

Sennheiser HD 660S2 Headphones Side Upright

They have a stiff plastic band and ear cups that are open letting some sound escape to the outside world and letting some sound in as well. These aren’t headphones for those who want to be isolated from the world. There are no frills like noise reduction and no wireless options. The 660S2 phones are designed to plug into your portable or stationary gear and listen.

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The ear pads are made of velour. Connections to the headphones are made with the same 2-pin push connectors the company has been using since the HD-414. With my older Sennheiser headphones, I’ve never had trouble with the cable connectors. They seem quite robust. And if something happens, they are easy to replace.

Sennheiser HD 660S2 Headphones Side Vu

The 660S2 comes with a standard 1/4” phone plug, and adapter to fit in the more common 3.5mm jack. There is also a balanced connector if your headphone amp or other equipment offers it.

Sennheiser HD 660S2 Headphones Balanced

The 660S2 makes some changes from older models, including a new ultra-light aluminum voice coil that reduces the weight of the driver. A new airflow system has also been added to this headphone, with the goal of minimizing distortion and eliminating obstructive artifacts.

Sennheiser HD 660S2 Headphones Exploded

These design changes have meant some changes to the efficiency of the driver, and it’s now 300 ohms. It means it will need a little more punch from a headphone amp or other source. I don’t think it’s a good match for a computer’s built-in audio system. Note: The newest Mac laptops have built-in amps that are a good match for this impedance.

Setup

Not much to report here. The headphones come in a cardboard box. Inside is the soft bag, the two headphone cords, an adapter, and the headphones themselves, along with a multi-language quick start guide.

Basically, you attach the appropriate connector to the headphones, plug them into your source, and listen away.

Sennheiser HD 660S2 Headphones Plugs

In Use

I was able to listen to quite a lot of music on these headphones and was able to compare them to my older Sennheiser HD 600 headphones, as well as some headphones from HIFIMAN.
I found the HD 660S2 headphones to be pretty comfortable even during long listening sessions (about 2 hours). I was always aware I was wearing headphones, but they were not a distraction. The headphones are light, as are the connecting cables. I had to be careful to not snare them on items near my desk or couch. The earpieces are lightly marked L and R on the metal band connecting the earcups. If you don’t know where it is, it’s not going to be easy to find. I see this issue over and over on headphones. HIFIMAN makes it easy to see, and so does Focal on their headphones. Often you are listening in a darkened room, and which side is which should be clearly marked.

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I listened to the headphones on a Schiit headphone amplifier (Valhalla 2) and directly from my FiiO M15 digital audio player. The FiiO drove the Sennheisers quite well but still found more ‘punch’ from the Schiit. The 300-ohm impedance of these phones will, I think, be happier the more power you can throw at them.

Overall, I liked the sound of these Sennheisers. They have deeper bass than any Sennheiser product I have heard or owned. The bass increase was particularly obvious compared to my older HD 600 headphones.

The midrange is quite good too, and female vocals sounded natural. High frequencies at first sounded a little muted compared to the HIFIMAN Sundara headphones, which use a planar driver compared to the dynamic driver that Sennheiser uses. Over time I came to believe the Sennheisers were a bit more natural in the high frequencies, while some other headsets, like the HIFIMAN were enhancing the high frequencies a few dBs. What you prefer is going to be down to a matter of taste. On some recordings, I felt the 660S2 headphones were short of treble. Some percussion instruments like triangles or symbols felt a little tepid, and the HIFIMAN were very good. On other recordings, like vocals and full symphonies, the 660S2 headphones sounded more accurate. I liked listening to both, but in the final analysis, I think the Sennheiser’s were a tad more natural sounding.

Imaging is very good on the Sennheiser phones with acoustic music coming across very strongly, and I could easily hear the placement of individual instruments across the listening space.

Here are notes on some of the music I listened to:

John Williams

John Williams “Jurassic Park”

Jurassic Park – John Williams’s score sounded very rich on the Sennheisers. I played back a 192/24-bit file, which has a wide dynamic range and lovely strings. The track called ‘Incident at Isla Nublar’ has some very deep bass on the Sennheisers that simply wasn’t present on the older HD 600.

Vaughan Williams

Vaughan Williams “Norfolk Rhapsody”

Vaughan Williams Norfolk Rhapsody – Bryan Thomson and the London Philharmonic do a wonderful job on some Vaughan Williams favorites. The HD 660S2 headphones did a lovely job of rendering the strings in the Norfolk Rhapsody and put me into the recording venue.

Rebecca Pidgeo

Rebecca Pidgeo “The Raven”

The Raven: Rebecca Pidgeon – this album is my old stand for listening to the sound of a female voice. My recording is an 88.2/16-bit FLAC. The track Spanish Harlem is a wonderful acoustic recording. Ms. Pidgeon sounded ‘in the room’ and the accompanying instruments were there in a very stable image.

Iceland

Iceland “The Eternal Music”

Iceland: The Eternal Music – A really high-quality recording from Harmonia Mundi. I auditioned this in a 96/24-bit file. There’s great dynamics here, and a choir. There’s epic music and an epic performance. The headphones never distorted or pinched the dynamic range.

Charlie Byrd

Charlie Byrd “Charlie Byrd at the Village Vanguard”

Charlie Byrd at the Village Vanguard – Not a state-of-the-art recording, but this 44/16 FLAC file sounds very good and captured a live performance. Imaging is important here and the Sennheisers rendered this 1960s recording very well.

Various

Various “Dark Side of the Moon”

Dark Side of the Moon – A remaster of their groundbreaking music in this 50th-anniversary edition CD and Blu-ray audio disc. I checked out the Blu-ray audio version but listened in 2-channel stereo rather than the ATMOS version. The music has a lot of movement back and forth, deep bass, ringing bells, and ticking clocks. The recording is still startling all these years later and the HD 660S2’s made it sound thrilling.

Conclusions

Sennheiser HD 660S2 Headphones AT a Glance

At $600 there are a lot of headphones in this price range. You can certainly find phones that offer wireless connections for example, but I’ve yet to hear a wireless headphone that can equal the sound of a high-quality wired headphone. I find that the Sennheiser HD660S2 is a quality headphone at a reasonable midrange price. Since sound leaks from the headphones, by design, it’s not a headphone for commuters or listeners with a lot of people around. It’s going to appeal to audiophiles who want natural sound, an open-air design, and solid comfort.

Likes
  • Build quality is good and the headphone is rugged. It’s mostly plastic, but a very high-quality plastic
  • The 660S2 headphones retain the Sennheiser ‘sound’ of wide frequency response without hyping particular frequencies.
  • The increased bass is natural. It’s not going to impress someone who craves unnatural bass, but it’s better and more natural than previous Sennheiser headphones.
  • I found these headphones comfortable to wear, but there is a slight pressure from them on your head. It’s not distracting.
Would Like To See
  • Better documentation. It’s dead easy to set these up, but I’d like to get some info on replacement parts availability, the use of the balanced plug, and some care tips.
  • The included drawstring case is nice but won’t really protect the headphones from damage on a trip. I’d prefer to see a hard case included
  • You have to hunt for the Left and Right ear markings which are embossed on a black metal part.

As is obvious, I liked these headphones, but they likely won’t appeal to every listener. Much of my music listening is to acoustic music (classical, jazz, soundtracks) and the HD 660S2 headphones do a fine job. If your tastes run more toward rock-and-roll or electronic music, you may appreciate the extended high-end from some of Sennheisers competitors.

By saying this I don’t want to give the impression that the Sennheiser’s are treble deficient. Anything but. But many headphones pump up parts of the frequency range to match some listener expectations.

The sound produced by these headphones is natural and uncolored. The bass, often a weakness in the Sennheiser brand overall, has been substantially improved. It’s always a challenge on an open-air design because low frequencies can escape the ear chambers. Same for all frequencies really.

Still, I think overall I prefer the open-air design for comfort.

Sennheiser has done an excellent job on these headphones. They are not a gigantic leap over the 20-year-old design of the HD 600, except in the low-end and overall smoothing of frequency response, but the HD 600 is an acknowledged classic and still popular today.