Sennheiser HD 660 S Review – Probably the Best Affordable Hi-Fi Headphones

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The problem with audiophile headphones for high-res listening is that they cost a fortune – and for a good reason. The best audiophile headphones are a masterpiece of engineering for which you have to pay the right amount of money. The Sennheiser HD 660S is different. The successor to the HD-650, the Sennheiser HD 660 S succeeds in highlighting its musicality and offering the high-fidelity listener a sound with a clear and nuanced bass, a lively and expressive midrange and a natural and very smooth treble.

The new Sennheiser HD 660S headphone is a masterpiece of engineering, replacing the legendary HD 650 model in the company’s portfolio. Capable of accurately and transparently reproducing all the emotions and nuances of music, the Sennheiser HD 660 S hi-fi headphones inaugurate a new transducer model developed by German engineers. In particular, this offers better control of the diaphragm movements and is equipped with extremely light aluminum voice coils, capable of providing an improved impulse response compared to previous drivers.

Sennheiser HD 660S Hi-Fi Headphones Review

Sennheiser HD 660S Specs

Type: Over-ear Noise Cancelling Headphones | Drivers: Dynamic | Drivers-Size: 1.7″ (42 mm) | Impedance: 150 Ohms | Frequency Response: 9 Hz – 45 kHz | Total Harmonic Distortion (THD): 0.04% | Audio Connectors: 1 x 1/4″ TRS and 1 x 4.4 mm TRRRS | Adapter: 1/8″ (3.5 mm) TRS | Connector Plating: Gold | Cable length: 9.8′ (3m) | Cable conductor material: Oxygen-Free Copper | Weight: 0.57 lb (260 g) – without cable

Pros

Beautiful, detailed sound with great clarity
Wide range of reproducible frequencies
Lightweight and comfortable for long listening sessions
Ideal for musicians but also for music lovers and audiophiles

Cons

Branded cables must be used because of the 2-pin connectors
Does not work with all mobile devices and requires a decent headphone amplifier.

Quick Review: Sennheiser HD 660S

The Sennheiser HD 660S are headphones designed for professionals and music lovers. It has an open design that allows the sound to be more natural and transparent. The driver size is 42mm, which allows for deep bass and rich highs. The ear cups are made of velour, the most comfortable material. Although the headphones are not capable of passively attenuating ambient noise, the listening experience offered is excellent and the price is quite reasonable.

Sennheiser HD 660 S Package

The whole thing makes a very solid impression, adequate to the class of the product. The graphic design of the packaging is rather ordinary. From the moment you take it out of the box, you can feel that you are dealing with premium equipment.

However, the price doesn’t indicate it (you know, in the audiophile world, if it doesn’t have buffalo leather upholstery and exotic wood stands, it’s not “premium”.

In the box itself, apart from headphones and documentation, two cables are waiting for us. Sennheiser HD 660S is delivered with an unbalanced cable (6.35 mm jack) and a balanced cable (4-pin gold-plated mini-jack) as well as a 6.35 mm jack to 3.5 mm mini-jack adapter (3 pins, 20 cm length). These cables are made with OFC copper conductors and benefit from reinforced Kevlar sheath.

The headphones are large and not foldable. The set does not include a case, but only the large, hard box, designed rather for storage than for transporting. More important, however, is that it was made very solidly and will undoubtedly be useful for storing and securing the headphones. This model is clearly dedicated to strictly stationary applications.

If someone assumes that the packaging of the Sennheisers tested is too modest for equipment that costs this much, you would be surprised by HD660S’s plain and modest appearance.

The HD 660 S are painfully minimalist. If we didn’t know how much they cost, we would probably never have guessed that it is a high-end headphone, but only after we’d listened to them would we realize it’s a very affordable hi-fi audiophile headphone.

Design & Ergonomy

In addition to offering audiophile reproduction quality, the Sennheiser HD 660 S hi-fi headphones benefit from a solid and light construction (260 grams). In terms of design and aesthetics, it cannot be denied that Sennheiser HD660S is very tasteful and elegant.

The headphones practically do not differ from their predecessors, and only their color has been changed, which is now completely black. The comfort of use is real with oval-shaped ear cups with velvet pads that respect the ear’s anatomy and surround it, pressing on them.

The thick headband padding also contributes to the Sennheiser HD 660 S headphones' comfort, which will give the listener many hours of listening without fatigue.

The problem with many over-ear headphones, even the high-end ones, lies in their use comfort. Such structures are often heavy to contain the necessary components, which translates into a felt pressure on the head.

The headphones are perfectly made, although the housing is mostly made of plastic (not counting the headband and the drivers’ external housing). Nothing here, however, creaks, cracks or smells like cheap plastic. The detachable cables are also very sturdy, and the ear pads are replaceable, so if they wear out over time, you can replace them with better ones.

The headband of the Sennheiser HD 660 S is made of plastic like most of the other elements. It is pleasant to the touch and appears to be of very high quality. There are no signs of weaknesses, but because it is still quite stiff, the risk of such breaking cannot be ruled out.

One of the major drawbacks one could point to is the fact that the earpieces cannot rotate/rotate – but is that really a flaw?

More like a personal preference. A closed structure would have been more enjoyable as you could use them at the office or with other people in the same room without disturbing anyone nearby. However, their charm is such that they have an open structure. For many, this is a feature, not a defect.

In terms of appearance and practicability, Sennheiser HD 660S are well designed and conceived to not cause any fatigue, even during long hours of work in headphones.

This is another round of applause to sound engineers and designers. As a bonus, music lovers can enjoy spending a lot of time with their favorite music without feeling discomfort.

The headband is softly padded and does not compress the head, and the transducer covers are perfectly contoured and neither too soft nor too stiff. Only after a few hours of non-stop listening do we start to feel any pressure, but it’s natural: using over-ear headphones requires taking breaks.

The earcups of the tested headphones are made almost entirely of the same material used in the headband. As I mentioned before, it is of really good quality, and I have no objections to it.

Sadly, the rotating earcups are to be missed, as they’re not available in this model. As a result, after removing the headphones from your head, it is better to put them on a stand immediately because, due to their considerable dimensions, keeping them hanging around the neck is not overly comfortable. Still, One of the great advantages of the Sennheiser HD 660S is its wide range of adjustments, perhaps the widest ever.

Sennheiser HD 660 S Features & Technologies

The Sennheiser HD 660 S high-fidelity headphones have been designed to offer optimal reproduction quality even with a low power source such as an audiophile player or a smartphone.

Its impedance (150 ohms) makes it possible to take full advantage of its acoustic qualities with high-resolution audio files played by an audiophile player. It can also use the balanced mini-jack output of any audiophile player or any compatible headphone amplifier to provide even more precise channel separation and stereophonic image.

The cable itself is made of oxygen-free copper and para-amide reinforcement, is topped with a 1/4 inch jack, but the set includes an appropriate adapter that is very long, thick, and solid.

Its dimensions have the disadvantage that it is not very convenient to use with a smartphone. For this purpose, it is better to use the second cable included in the set, with a 3.5 mm jack.

Nevertheless, it is worth noting that the Sennheiser HD 660S, with its 150 Ohms, works with most smartphones on average. Apart from smartphones like Samsung Galaxy S20, LG V30, LG V40, and LG V60 ThinQ, most devices are unlikely to deliver enough power to these headphones. Well, unless you happen to have a mobile DAC for this purpose.

Sennheiser HD 660 S Sound Quality

The Sennheiser HD 660 S are fully open, over-ear headphones, the heart of which are the high-quality dynamic drivers known from the HD 700 model. They have an impedance of 150 Ohm, but at the same time they boast a relatively high efficiency of 104 dB to deliver loud and clear music.

The frequency response declared by the manufacturer is 10 Hz to 41 kHz, allowed it to obtain the Hi-Res Audio certificate.

Taking up the sober and refined aesthetic of its predecessor, Sennheiser HD 660 S headphones are more versatile since they can be used both with an audiophile player or a smartphone or with a headphone amplifier to demonstrate their audiophile qualities.

A valuable quality of Sennheiser HD 660 S is the ability to captivate from the moment they are put on the ears. The headphones continue the traditions of their predecessor. They are an exceptionally musical model, focused more on the fun of listening sessions than analyzing every audio nuance and pointing the artist’s errors.

Music Genres

During testing, I couldn’t find a music genre that the HD660S didn’t clearly match. From classical music to rock, metal, nu-metal and DnB. To electronic music, rap, jazz or dubstep. The Sennheiser HD 660S played fantastically. As it is an open design headphone, people who like headphones with tight and well-extended basses will be able to use it.

Nevertheless, the open-back architecture results in better acoustic properties. Everyone in our proximity can hear what we are listening to in return. And vice versa – the surroundings’ sounds can be heard in our ears. So, if you want to get the best experience, it is best to use models with such a construction in a quiet corner, away from the rest of the world.

Gaming

The HD 660S open-back headphones are also surprisingly good at reproducing sounds in games, allowing you to enjoy a scene full of elements positioned correctly in the soundstage and well-reproduced basses.

A note regarding the soundstage; the scene in the Sennheiser HD 660 S is coherent, but at the same time, small for open headphones.

The distances between individual sources are also limited, resulting in lower instrumental separation. Of course, the distinction between individual instruments is not a problem. Yet the headphones themselves do not expose uncharted territory like the Sennheiser HD 800S.

Regardless, if you have a good quality DAC connected to the computer, these headphones’ dynamics result in a sensational gaming experience – music listening, too

When it comes to gaming, a detailed analysis of individual bands' quality is much less important. What matters more is the effect of immersive Sennheiser HD 660S can convey the impression of space and auditory imagery that gamers need; thus, perceive your opponent's location in Counter-Strike, PUBG, Fortnite, Battlefield, pinpointing specific sounds in the soundstage.

Frequency Response

HD 660S’s drivers, designed from scratch, with a diaphragm made of a fabric composed of stainless steel, play a significant role, indicating that Sennheiser HD 660S sounds beautiful in every frequency range. These headphones sound good in absolutely any conditions, and the only thing they don’t do is overwhelm you with low frequencies.

In fact, the bass’s selectivity is truly impressive, especially in modern music, with a lot of low frequencies that would otherwise get lost in the mix with some headphones. You can hear every note here.

For an open-back headphone, Sennheiser HD 660 S offers a solid bass foundation. Low tones are clearly emphasized, although they do not stand out to the fore; rather, they constitute a midrange background, which plays the leading role. The mid frequencies are wonderfully clear.

You can hear absolutely every nuance in the sound of voices, every detail in fast transitions played on the electric guitar. The midrange is by far the biggest strength of the new Sennheisers. It has two interesting flavors: the soft and the very energetic. They sound exceptionally soothing, even intimate.

It deserves special recognition as the HD 660S performs with success female voices, adding a lot of charm to the whole message. The highs are incredibly melodic and beautiful-sounding—still a bit grainy but not over the top.

The treble is strongly exposed, at times giving the impression of artificially raised. It is true that they never come to the fore and allow the midrange to shine, but their influence on the overall character of the whole presentation remains clear. Even when we listen to a song with many strings or cymbals, the trebles’ sound is not overly harsh and unpleasant.

Soundstage

Sennheiser’s HD 660S headphones are astonishing with the soundstage’s clarity and width that I would expect from headphones three times more expensive. In these headphones, connected to the appropriate sound source, you can hear every detail of the music played.

Thus, the Sennheiser HD 660S achieves what audiophiles desire from musical equipment – they reproduce music as reliably as if we were listening to it live in a perfectly acoustically adapted concert hall. And they do it for approximately $500. Something amazing.

Buyers should be aware that the Sennheiser HD660S hi-fi headphones are very demanding for the sound source and audio file format – like most headphones of this class. I’m not just talking about the device they are connected to, but mostly about the source file’s quality. With 192 kbps music files, you can hear all the artifacts and imperfections of compression.

After switching to high-quality files, e.g., in Tidal Hi-Fi, the sound starts to sound as it should. Since Sennheiser HD 660 S are open-back, the outside listener may think that these headphones sound even worse than cheaper consumer models.

In fact, listening to the sound in 320 kbps AAC Sennheiser HD 660S brutally exposes the actual quality of streaming services. However, it is enough to reach for FLAC files, and the feeling changes dramatically.

Conclusion – Is Sennheiser HD 660 S Worth Buying?

It was a fantastic experience to test a product as successful as the Sennheiser HD 660S. When it comes to value for money, the new Sennheiser headphone model is basically second to none. I dare to say that I see no reason why the vast majority of music lovers should pay extra for the top model HD 820 or HD 820S.

Yes, the more expensive headphones are even better built and sound even more lifelike and organic than the HD 660S, but not enough to pay several times more than what Sennheiser HD 660S costs. However, for the price, we cannot criticize much about Sennheiser HD660 S.

Like its predecessor, Sennheiser HD 650, the HD660S is also suitable for experiencing audiophile enjoyment at home and critical listening to mixes in a recording studio.

However, while the classic HD 650 always sounded somewhat dry for most audiophiles, the HD 660S should be more balanced, even though they cover the same frequency spectrum: from 10 to 41,000 Hz. Most likely, as with Sennheiser HD 650 – I’m sure that the Sennheiser 660S hi-fi headphone will also gain a high status over time.

Pros

Beautiful, detailed sound with great clarity
Wide range of reproducible frequencies
Lightweight and comfortable for long listening sessions
Ideal for musicians but also for music lovers and audiophiles

Cons

Branded cables must be used because of the 2-pin connectors
Does not work with all mobile devices and requires a decent headphone amplifier.

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