Sennheiser HD 660 S – A Symphony of Audiophile Excellence

Sennheiser HD 660 S – A Symphony of Audiophile Excellence

Written by Mark Williams, In Headset, Published On
January 1, 2024
Last modified on January 3rd, 2024

Sennheiser is known for designing simple headphones that let sound shine. I’ve had various models, including my reference HD 600, and listened to its goods since childhood (HD 414 with yellow pads!). Since the naming scheme implies that the HD 660S model is better, this review was a good chance to find out. I spent over three weeks testing the Sennheiser HD 660S for critical and casual listening and editing to determine if it belongs in your headphone collection.

Specifications Of Sennheiser HD 660 S

Sennheiser HD 660 S

Feature Specification
Type Over-ear, open-back
Transducer Principle Dynamic
Frequency Response 10 Hz – 41,000 Hz
Impedance 150 ohms
Sound Pressure Level (SPL) 104 dB (1 kHz/1Vrms)
Total Harmonic Distortion (THD) < 0.04% (1 kHz, 100 dB SPL)
Ear Coupling Circumaural (around the ear)
Connector 6.3 mm / 1/4″ stereo plug with 3.5 mm / 1/8″ a

What is In The Box?

Sennheiser HD 660 S

  1. HD 660 S Sennheiser headphones: Primary headphones with over-ear cups.
  2. Removable Cable: Removable cable featuring a 6.3mm stereo plug.
  3. Symmetrical cable: Some packages contain balanced cables with various connectors.
  4. ¼ inch to 3.5mm connector: An adapter for 6.3mm to 3.5mm.
  5. Manual: Instructions for use and upkeep.
  6. Storage Box: Headphone carrying case.
  7. Warranty Details: Product warranty paperwork.

Quality & Comfort Of Sennheiser HD 660 S

A sleek matte-black finish covers the HD 660S’ HD 600-series chassis. Except for the outside grills and inner headband, the HD 660S is primarily plastic. This headphone design is still one of the most robust and dependable. I’ve owned two Sennheiser headphones and never had a build quality issue. Only the pads, which wear out rapidly, will require replacement on this headset. Your pads may need to be replaced every year to maintain their sound. The HD 660S has excellent comfort and build quality. The primarily plastic design makes things relatively light (260g), so I doubt anyone will have weight difficulties with them.

Sennheiser HD 660 S: The Sound Quality

Sennheiser HD 660 S

I absolutely love these Sennheiser headphones for classic rock, my favorite genre. They’re not flawless, and—more crucially for the HD 660S—value is a factor I’ll explore later in this review. This sound section will compare the HD 660S’ tonal and technical performance to its competitors and Sennheiser’s other products, including the DROP X Sennheiser HD 6XX and HD 58X Jubilee.

Sennheiser HD 660 S: Dynamics

I think the HD 660S has good dynamics. Despite the HD 600-series’ lack of punch, the HD 660S did marginally better in this category. Despite not being the strongest, the HD 660S had some punch. I thought microdynamics was well-defined since all the components had tension and existence. I think the HD 660S does well in this area, but the Sundara and DT 1990 Pro are more engaging and lively.

Sennheiser HD 660 S: Overall Experience

Sennheiser HD 660 S

The Sennheiser HD 660S comes in a vast, foam-lined black box with a hinged top, two 3-metre “Y” connectors, and a short converter cable. The case stores the headphones, not transports them. Given their open-back style, you’ll require a carrying case if you take them often. The lack of folding hinges indicates that these headphones are for home use exclusively. Like Sennheiser’s similarly priced over-ear headphones, they include ample headband cushioning and wonderfully plush 70mm x 40mm ear cups. The 260-gram weight is light on my head and pleasant for extended durations, with little heat buildup. The clamping force is right, and the ear cups’ little swivel fits my skull nicely. The headband’s notches allow you to recall your size by counting the clicks of each adjustment of the hard metal mechanism.

How do I connect the Sennheiser HD 660S?

One cable terminates in a 1/4-inch TRS jack, which can be converted to the practically universal 3.5mm TRS jack with the short adaptor cable (which adds 24cm to the generous 3m cable length); the other cable ends in a 4.4mm, 5-pin TRS (Pentaconn plug), which will only be useful if you have an amplifier with a “balanced” (aka differential) output port like the excellent Most folks would have preferred the 1/4-inch cable and 3.5mm jack. Some “balanced” headphone amps use 4-pin XLR connections; hence, a balanced cable (CH 650 S) is available separately.

Does the Sennheiser HD 660S block noise well?

Because open-back headphones are unenclosed, the HD 660S barely blocks ambient noise. We found poor passive isolation in the Sennheiser HD 660S. Someone close will hear your audio as well as your surroundings. That’s OK in private, but the HD 660S requires alternative headphones for less-friendly circumstances.

How Does The Sennheiser HD 660S Sounds?

Sennheiser HD 660 S

Listening to the Vitamin String Quartet’s cover of Girls Like You shows the HD 660S’ good portrayal of space in music, performing great closeness while maintaining enough apparent distance from my head. Open-backed headphones excel here. The melody’s prolonged, bowed sections and plucked strings’ “attack” seem realistic.

At 0:38, the violin floating to my right sounds excellent. Switching gears, Close to Me by The Cure (2006 remaster) shows the headphones’ spatial ability on an essential stereo mix. For anyone who’s only heard this track on a car radio or boombox, the “localizability” of Robert Smith’s percussive breathing in the far left and right of the image in this headphone may make you look over your shoulder the first time you hear it. It seems that Smith pioneered AMSR.

Sennheiser HD 660S Pros and Cons

Pros Cons
Natural and Balanced Sound Signature Limited Noise Isolation
Improved Transducer Technology Not Ideal for Commuting
Open-Back Design for Spacious Soundstage Price Point
Comfortable Fit for Extended Use Amplifier Recommended
Detachable Cable for Convenience
Crisp Highs and Clear Mids

Should I Buy Sennheiser HD 660 S?

The Sennheiser HD 660 S maintains the company’s high-quality audio reputation. The enhanced sound character upgraded transducer technology, and comfort appeal to audiophiles, music fans, and professionals seeking an immersive and accurate listening experience. The open-back design and price point may not suit everyone, but audiophiles and comfort seekers will love the HD 660 S.


Must the Sennheiser HD 660S be burned in?

No, because burn-in is fiction, we can only conclude that the headband was expanding and ear pads molding to match your anatomy improve performance with usage.

Are ear cushions replaceable?

Yes, HD 660 S ear cushions are interchangeable. This is helpful for consumers who want to maintain their headphones or customize the ear cushions.

How does HD 660 S sound isolation?

The HD 660 S is an open-back headphone with little noise isolation. Open-back headphones are preferred for their larger soundstage; hence, the design was purposeful. However, this makes them unsuitable for loud conditions.

Can I game on the HD 660 S?

Gaming is possible with the HD 660 S, especially for audiophiles. The open-back design creates a more immersive soundstage for gaming. However, the absence of isolation may let in outside sounds.

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