Review: Sennheiser HD 660S

Classic in renewed costume

Sennheiser's best in the 600 series is the safe choice in this class.

Sennheiser HD 660S
We think
Silky smooth sound rich in details, beautiful vocal reproduction and warm, full sound.
Limited sound pressure and deep bass.
  • Type: Open, over the ear
  • Principle: Dynamic
  • Collapsible: No.
  • Microphone / remote control: No / no
  • Cable: 3m 6.3mm incl. 3.5mm adapter + 4.4mm balanced
  • Elements: 45 mm
  • Impedance / sensitivity: 150 ohms / 104 dB
  • Frequency response: 10-41,000 Hz
  • Weight: 260 grams (without cable)
  • Color: black

Few headphones have had legend status as long as the Sennheiser 600 series. The most generous is the HD 660S, which has been our reference among open, dynamic headphones in this price range. They are compact, lightweight and play well on everything from simple headphone amplifiers, to expensive high-end hi-fi. The HD 660S are not completely neutral, but so well balanced that they are a well-suited reference point.

The Senn hoists come with a proprietary 3 meter long cable, a carrying case and a balanced cable with a 4.4 mm balanced Pentaconn plug. Unfortunately, there are not many headphone amplifiers with Pentaconn connectors, apart from Sennheiser’s own. The earbuds are similar to those on the Audeze LCD-1, angled slightly in relation to the padded hoop, and for the most part the HD 660S is made of plastic. It provides low weight and good wearing comfort.

Sennheiser HD 660S in use

The fabric-covered ear pads lie softly on the head and the oval shape at least fits my ears perfectly. They are not at all unsuitable for portable use. With a resistance of 150 ohms and 104 dB sensitivity, you get decent sound, but there is no doubt that an Audioquest Cobalt connected to the phone, gives far better sound in the Sennheiser.

The large oval ear pads and moderate pressure on the head, provide excellent wearing comfort. Like the Beyerdynamic headphones, these are among the most comfortable headphones to wear over time. Had they been collapsible, they would have been perfect to take on a trip, even though they are not as compact as the LCD-1.
Those familiar with earlier versions of the Sennheiser HD 600 series will hardly be disappointed with the HD 660S. The soundscape is more open and more detailed, the bass is more clearly defined and timbres come out much better in the soundscape. They are not as analytical as the Beyerdynamic DT 1990 Pro, and the sound is warmer and more listener-friendly compared to the LCD-1.

Strings are beautifully defined, the same as you say about vocals, but there is a small veil over the treble that dampens the aggressiveness of e.g. hard hitting rock. It is correct to say that the balance in the sound provides a very pleasant listening experience. There’s more air in the sound on the Hifiman Sundara, and tighter and more dynamic bass in the LCD-1, but that does not deprive the HD 660S of any of its qualities.


The Senn hoists feel like an old, tailored coat. It may not be ultra-modern or high-tech, but it fits every time you put it on, and the classic ‘Sennheiser sound’ is very addictive. You get sharper dynamics and sharper detail in other headphones, but few others have as many positive all-round qualities as a pair of Sennheiser HD 660S.

HD660S frequency
Sennheiser HD 660S measured with miniDSP EARS and REW. Compensated for what miniDSP thinks is subjectively linear.
Slightly careful with energy in the bass below 100 Hz, and from the midrange around 1 kHz the unrolling starts very carefully. With the exception of a peak around 8 kHz to bring out the details and the air.

Also in this test

Hifiman Sundara

Test winner in open class

Hifiman Sundara is not only the best buy in this class, you also get the best sound.

Perfectly balanced sound with potent bass and buckets of details. Super-defined sound image with almost complete qualities.
The size and weight can be inhibiting.

Audeze LCD-1

High-end headphones for your smartphone

Audeze LCD-1: There is no better sound for portable use in this price range.

Compact, light and perfect for mobile. Glass clear and neutral sound, with live bass reproduction.
The bass rolls off early and the soundscape is not as fine-meshed and refined as the reference.

Neumann NDH 20

Non-engaging first attempt

Legendary microphone manufacturer fails to grab us with its first headphone model.

Appealing appearance, great aluminum finish and decent comfort. Seems to be a comfortable load on amplifiers, does not change sound very much from amplifier to amplifier.
The sound is dark, with too little detail at the top. It also sounds too sharp for our liking.

Fostex T60RP

The music unfolds

Whether it is because they are semi-open is not known, but the Fostex T60RP has cleaner sound than most closed in the class.

Great resolution, rich bass and large room. Very musical presentation.
Very heavy duty! Forget about using these with your mobile. Slightly reclining treble. Looks like industrial hearing protection…

Denon AH-D5200

Fabulous closed headphones from Denon

Denon AH-D5200 is among the very best closed in its class.

Super nice and detailed sound image with lots of timbres. Nice workmanship and nice comfort.
The treble reproduction could have been a little more fine-grained.

Beyerdynamic Amiron Home

The most sensible choice

The Beyerdynamic Amiron Home is an exceptionally successful all-round headphone.

Detailed, warm and open sound image with very potent bass. Excellent wearing comfort and high quality.
Requires a serious amplifier. May sound a little too soft for someone's taste.

Beyerdynamic DT 1990 Pro

Sharp analyst

The studio qualities are the strengths and weaknesses of Beyerdynamic DT 1990 Pro, must be tested before purchase.

Super resolved and analytical. Steel control in the bass, very open and detailed sound, and excellent wearing comfort.
The analytical grade gives sharper, and less listening-friendly sound.

Sony MDR-Z7M2

The entertainment is saved

Sony has improved its premium model Z7 with technology from the flagship Z1R. The result is even more striking.

Extremely comfortable ear pads. Great quality feeling, a lot of metal. Hefty bass, very entertaining listening.
Dynamics could have been more outspoken, and the bass faster. Takes some focus from the overtones and air in the music.

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