[Maitre Renard]

Hello !

I am considering purchasing the HD 660 S that cost around 300 euros at my side, in addition to my Denon 5200, which I love too much

What could be the listening experiences compared to other open models like hd 600 or hd 540 ( reference 1 is my favourite ones! ) ? Would the lower impedance of 150 ohms allow to use them directly with smartphone ?

Many thanks in advance!

 

[HA-1]

Sennheiser shows HD 660S2:

"With the new HD 660S2, Sennheiser is expanding the spectrum of the 600 headphone family with a model that is supposed to bring more resolution and more power with low tones.

In particular, the sub-bass range of the HD 660S2 is supposed to provide special emotionality. At the same time, according to Sennheiser, there has been an acoustic fine-tuning with optimised airflow around the transducer and a lighter voice coil, which should bring out the dynamic effect and impulsiveness of the music reproduction even better. The transducer beading has also been redesigned, which is said to have lowered the resonance frequency from 110 to 70 Hertz.

In particular, the precision and detail in the lowest frequencies have been improved compared to the predecessor. Developed in Germany and manufactured at the Sennheiser factory in Tullamore, Ireland, the headphones have an impedance of 300 ohms, and the ear pads and headband are softly padded. The HD 660S2 is supplied with 2 different cables and an adapter for 3.5 mm mini jack -- Sennheiser-Hearing.com ".

HD 660S2 review by German c't - Magazin für Computertechnik (06-2023, p.90):

"Taut headphone: Sennheiser has revised the neutral open headphones HD 660S, but the S2 comes at a price. For years, Sennheiser's HD-600 series headphones have been the first choice of music producers and sound lovers who prefer neutral, balanced reproduction. With their ear-enclosing pads, the headphones are pleasantly light to wear. They do not shield the wearer from the outside world, which is why they are only suitable for quiet environments. The Sennheiser HD 660S were previously a tip for those who were looking for a model in the series that could do without a powerful amplifier. Compared to the HD 600 and HD 650, the HD 660S has a lower nominal impedance of 150 ohms. This means that it can also be used with laptops and even smartphones - as long as they have an analogue jack socket.

The HD 660S2 successor, which has now been introduced, loses this advantage. Its dynamic transducer has a coil wound with thinner wire and a nominal impedance of 300 ohms. This puts the S2 on a par with the HD 600 and HD 650, and it is about 2 decibels quieter than the old HD 660S. The advantage of the 300-ohm coil is its lower weight with higher magnetic force. This allows the S2 to reproduce impulses more precisely, which not least improves spatial localisation in the stereo panorama. In addition, the engineers have increased the stroke of the transducer. Low frequencies below 100 Hz are now reproduced somewhat more powerfully, whereby the increase of around 2 decibels at 50 Hz is measurable but hardly audible.

All in all, the HD 660S2 not only sits a little tighter on the head, but also sounds like it and plays a little richer in the bass range than the HD 660S. However, these are nuances that are only noticeable in direct comparison. The neutral basic character with balanced bass, mid-range and treble remains the same. Since the frequency response hardly changes, you can even apply the old headphone profile of the HD 660S to the S2 in equalisation programmes like DearVR Mix. As an alternative, the Sennheiser HD 600 (approx. € 400) sound a little brighter. The Neumann NDH 30 (€ 630) are less noticeable in the lower mid-range between 100 Hz and 300 Hz and therefore sound slimmer. In addition, its treble sounds somewhat softer, which is close to the listening impression of calibrated speakers. Ultimately, it is a matter of taste which one you like better. Sennheiser pays well for the small sound improvements of the HD 660S2. The recommended retail price has risen from € 500 to € 600. Sennheiser justifies this with the more expensive transducers and the higher reject rate due to stricter quality controls. The old HD 660S, which is now being sold at the street price of € 400, is to disappear from the portfolio in future. Those who forgo the last ounce of precision can save a lot of money with it."


HD 660S2 review by German HiFi-Magazine STEREO (05-2023, p.66):

"Make good things better without exploding the price. That was the task when it came to developing the brand new Sennheiser HD 660S2 open dynamic headphones.

The family-owned company Sennheiser from Lower Saxony sold its soundbar and headphone division to the Swiss hearing aid specialist Sonova in 2021 and has since concentrated on microphones and studio technology, while the new owners set about modernising and improving the model range piece by piece in the highly competitive market of high-quality headphones. The company remains faithful to the dynamic principle of sound transducers, even though magnetostats have established themselves in this price range in recent years and have gained a good reputation. In terms of sound, magnetostatic headphones, which use strong magnets to cause a foil to vibrate, are a serious alternative, but they have two disadvantages: The magnets used in these headphones add a considerable amount of weight, which can have a negative effect on wearing comfort, and very few magnetostats are suitable partners for simple headphone connections built into devices or even for mobile devices. The task for the HD 660S2 was first and foremost to give it a more powerful foundation in the very lowest frequencies, which would give it even more body and noticeability, without losing the fundamental qualities of its predecessor. For this purpose, among other things, the voice coil construction was revised and raised to an impedance of 300 ohms, as was already the case with the HD 600 and HD 650. According to Sennheiser, this new aluminium voice coil increases the magnetic field strength and is supposed to ensure further improved impulse control, i.e. less distortion and thus a cleaner, more natural sound image. Changes have also been made to the housing, in particular the air flow conditions have been taken into account and adjusted so that resonances occurring due to the air flow in the housing are now better damped. The result is an improved impulse response over the entire frequency spectrum. All in all, all these factors, including the doubling of the sound pressure at the lowest frequencies, contribute to maximum precision, speed and resolution in the reproduction, if you follow the developers in their presentation.

A very important point about headphones, which we cannot emphasise often and intensively enough, is comfort and fit. After all, the best-sounding headphones will live a shadowy existence unused most of the time if they are uncomfortable to wear. This is where you can feel the HD 660S2's many years of experience in finding the ideal mix of contact pressure and permanently relaxed wearing for almost any head shape and size as well as any anatomy of your ears. Thanks to the low weight of only 260 grams and the large, soft ear pads with velour cover, the 660S2 is very comfortable to wear even after hours and even when wearing glasses. In addition to the lightness of being, the open design helps the 660S2 to listen to an entire opera without getting tired and without heat build-up. In this respect, it has a head start on the vast majority of its competitors, quite independent of its sound qualities, which we will come to in a moment. And if you belong to the category of music lovers who like to bob their heads back and forth while listening - please, the Sennheiser will remain in its original position on the head with stoic calm. Also pleasing and worth mentioning are the interchangeable cables and ear pads, while the search for left and right shells once again requires detective search manoeuvres. Small tip: On the left side, there are three visible and tactile points on the holder! Should you wonder how Sennheiser manages to deliver such lightweight headphones in high quality: The low, wearer-friendly weight is also achieved through the generous use of plastic in the company's own factory in Ireland. There, it is also ensured that one pair of headphones sounds like the other, as the drivers are manufactured with minimal tolerances and their consistent quality is randomly checked.

The result is that the HD 660S2 is not at fault in terms of sound quality. Fortunately, the development department resisted the temptation to turn a very good € 500 headphone into a populist € 600 bass monster. With many pieces of music, one hears only a slight tonal difference between old and new. Only when a recording is really well done do you notice the additional pressure in the frequency basement and at the same time a somewhat finer, tidier reproduction with fewer artefacts, which also seems much airier. We discovered a first example of the gentle but nevertheless pleasing tonal overhaul when we listened to a string quartet by Guiseppe Verdi. In direct comparison to its predecessor and in relation to the HD 650, also in the € 500 price range, the S2 sounded more open, airy and spacious. At the same time, despite more warmth in the sound image, it was always a touch more precise and cleaner, as became clear with Johnny Cash's "Personal Jesus" Similarly, when we switched from classical music to jazz and funk. When Stanley Clarke sang "School Days", it always sounded a touch warmer, yet drier and remarkably more dynamic. A similar picture emerged when we turned our attention to other virtuosos such as Marcus Miller or Ray Brown on double bass or Sonny Rollins on saxophone: The HD 660S2 never played spectacularly to the fore, but due to its less anaemic reproduction it was convincing not only with basses and single instruments or small ensembles, but also with orchestral music such as Mahler's 4th Symphony. Surprisingly, however, cracking pop songs from Yello (Rhythm Divine) to Cameo (WordUp) melted away the differences to an almost negligible degree.

The successor to the best-selling HD 660S was better all round than its successful predecessor thanks to a few modified details. Due to the overall more powerful, but once again tighter bass reproduction, the sound image seems fuller and more natural, without thickening up. There is no doubt that sensitive experts were at work. 300 Ohm impedance, weight 260 grams, efficiency 104 dB - not a perfect partner for mobile devices, but most headphone amplifiers will be able to drive the Sennheiser without any problems. For best sound, however, a high-quality headphone amplifier should be used. Rating of the sound quality: 87 points out of 100." For comparison, HD 800: 88 points, HD 800S: 89 points (out of 100).


HD 660S2 review by German HiFi-Magazine AUDIO (05-2023, p.52):

"With extra bass - Sennheiser has revised the legendary HD 660S. These headphones have a firm foothold in the studio but also among music fans who want a particularly balanced sound image. The S2 version now comes with improvements, especially in the sub-bass range.

Sennheiser is well aware of the HD 660S's position in the market and has therefore deliberately taken a cautious approach to the new edition. The open design and the powerful dynamic drivers with a diameter of 38 millimetres have been retained. This has earned the headphone an excellent reputation in recording studios in the past. Because of its balanced and detailed sound, the HD 660S is indispensable in mixing and mastering. The most important features therefore remain untouched in the S2 model. However, the Sennheiser engineers did intervene a little in the sound. It's about the sub-bass, i.e. the frequencies that are so low that you normally can't hear them, but you can feel them physically. Here, Sennheiser has given the HD 660S2 a turbo. Frequencies from about 50 Hz down to 8 Hz (!) are said to be reproduced with twice the sound pressure compared to the predecessor. This was achieved by improved aluminium voice coils, which are lighter and therefore have less moving mass.

The HD 660S2 weighs only 260 grams. Thanks to the oval design of the capsules, the headphones still offer a comfortable fit that does not lead to pressure points or signs of fatigue even during long listening sessions, which we can confirm in the test. The ear cushions are covered with velour. This makes them very comfortable to wear. Only the contact pressure of the headphones seemed relatively high to us in the test. Music fans with particularly large heads might have problems here. The open design is famous for its playfulness and liveliness, which the headphones convey. However, it also has the disadvantage that external noise is clearly audible and can make undisturbed playback difficult in certain environments. In the studio this is usually not a problem, but at home or on the road one should be aware of it. The noise caused by a moving underground (subway, metro) comes through clearly audible.

Clever: the cable can be replaced in two easy steps so that it can be easily replaced if it gets damaged. Great: the manufacturer includes two cables, which gives the HD 660S2 flexibility in use. In addition to the obligatory 6.3 mm jack cable (an adapter to 3.5 mm jack is also included for mobile use), the owner gets a balanced cable with a Pentaconn connector. This shows the studio genes of this headphone series. The impedance of 300 ohms also allows mobile use with a smartphone. The level was always sufficient in the test. If you want to transport the headphones more often, a simple cloth bag is included, but you have to buy a sturdy hard case separately.

In the test, the Sennheiser HD 660S2 hi-fi headphones offered a tonally balanced sound quality with an earthy low bass that was nevertheless not exaggerated. The bass was the foundation of the overall sound impression and gave the music a natural sound. The midrange and lower treble reproduced wonderfully transparently, conveying a wide soundstage, while the upper treble produced lively impulses. The sound was incredibly precise and detailed, with a clarity and consistency that excelled at reproducing any genre of music. The HD 660S2 delivered an exceptional soundstage with excellent instrument separation.

In the test, it quickly became clear. The Sennheiser HD 660S2 is suitable for a wide variety of music genres. Whether we put pop, rock, jazz or classical music in front of it, the HD 660S2 always delivered impressive results, every detail of the music was audible, yet it never became tiring or too analytical. These headphones speak one language above all: sound! Everything about it is geared towards the optimal reproduction of music. Every detail becomes 'visible', every playing error is ruthlessly revealed. Add to this the enormous joy of playing, which always brought a smile to the listener's face when fed with jazz, funk or fusion. Bad mood? No chance!

Excellently balanced sound, abysmally deep bass, somewhat high contact pressure, outstanding workmanship. Sound rating: 90 points (out of 100)." For comparison, HD 800: 95 points, HD 800S: 96 points (out of 100).

 

[Maitre Renard]

Actually I’ve heard about the S2 but it costs almost two times more than the S1, and the higher impedance probably would not be good for my case although I believe that this is the great headset.

BTW what is the difference between the 660 and the 650 ?

 

[rfernand]

I just got mine last night so I can’t say I’ve fully understood the 660 S2. I’d say it’s an “unveiled” 650. Where the 600 is relaxed, this guy is more in your face. The 650 sounds warmer than the 660 S2 to me. Bass here is more present.

Maltre: HD 600 retails for $400, can be found new for ~$250.