Sennheiser HD 660 S Open, Dynamic Lightweight Circumaural Headphones with Low Impedence and Improved Transducer Design for Audiophiles, Black

There were several reasons to add these "Sennheiser HD 660S Over-Ear Open Dynamic Headphones - Black" to a small but growing personal mini-collection.The packaging is essentially to expectations, card sleeve enclosing a solid box in which are the 'phones, cables and data booklet. The only issue is that the box is a VERY TIGHT fit in the sleeve and difficult to remove without damage to the sleeve, not that all will care about that! Once extracted, a thick lump of dense foam packaging within the box pushed its two sections outwards and the cause of the difficulty.Included cables are a 4.4mm balanced and a 3.5mm unbalanced, both 3m long and rubberized. There is an option for a balanced XLR cable should that ever be needed. As best known, coiled versions are not available as potential alternatives to those provided as they have a reputation for kinking. Rather than the gold-plated brass headphone adapter most manufacturers include, there is a short adapter cable ending in a plastic-bodied socket. The connectors linking with the earpieces are not obviously keyed other than being labelled L and R, respectively, on the outside.The earpieces lack any obvious labelling for side (L or R). The cable connectors are marked but the lettering is small, black on black and barely rise beyond the general surface. The key is the gold S logo on each unit which should be oriented to the rear.The headband is the expected thick, broad band with deep velour-covered foam pads to either side of centre with sufficient adjustment for different head sizes, hairstyles etc. The ear-pads are also velour-covered which should be longer-lasting than the 'leather' found on lesser models and that usually need replacing within two years; these should last several years. Both sets of padding are sufficiently thick and comfortable.While immediately comfortable to wear, and likely to be just as comfortable after several hours, they are quite lightweight as plastics are used extensively, a significant surprise at the price paid. Were construction of carbon-fibre, glass-fibre or a honeycomb composite as used in the aviation industry (subject to suitability); the weight would be similar but perception of construction standards would probably be higher. Regardless, construction is to an adequately high standard although a hard case may be desirable should they need to be transported between home and studio or between venues; the 'phones are not designed to fold so is likely to be large and preferably internally sculpted to fit. At home, a suitable headphone stand (a polystyrene head?) could be a worthwhile addition.Designed for audiophile, professional studio or monitoring purposes the HD660s' perfectly flat mid-range and lower-treble - the portion of the audio range most relevant when monitoring or producing - is outstanding and probably exceeds almost everything within their price range. Overall frequency response is quoted as 9 Hz to 41500 kHz but without a specified variation at the extremes. Sub-bass performance out-of-the box is less impressive.The HD660s generally requires a headphone amplifier and that is how it will be later used; a burn-in period using a radio's headphone socket as a source will follow almost immediately with the 'phones buried under a pile of cushions to deaden the leaking sound over the minimum of two or three days' continuous play it involves - it isn't necessary to listen, especially if in a bedroom at night!The amplifier owned offers two functions dedicated to an older Sennheiser model that is now manufactured by another company and rebranded. That model has widely recognized performance issues that the amp can resolve. Although not specifically intended to support them, it was suggested by an independent professional audio lab that there is a shortlist of Sennheiser models that each benefit when partnered with the amp; the HD660s is one, supported not equally but even better! That information was previously unknown.Having purchased the amp to use with other owned headphones, it was initially thought not to be fully functional as its benefits were not audible with either. Questions were raised with the manufacturer and some clarification followed but additional questions were raised but not yet resolved. Once support for the HD660s was known via another source, their purchase was initiated.Personal curiosity about the amp's benefits needed to be satisfied and results for both functions are highly favourable, very evident even for older ears. With both working in consort, low-bass performance is improved, the sound rounder and more characterful helped by a slight rise and smoothness in the high-treble area while the expanded sound-stage is dramatic having eliminated the sense from the HD660s alone that performers who previously appeared to essentially be shoulder-to-shoulder were now spread across a wide area with a well-defined left, right and centre, not each in a single location but with individual isolation. After burn-in, performance should be smoother and more impressive.As a headphone amplifier is almost indispensable, purchasers should undertake their own research to ascertain which best meets their budget and usage requirements as prices range from sub-£100 to low-thousands! Personal choice, initially incidental and with no expectation that the HD660s were soon to be purchased, may have resulted in the perfect partner without breaking the bank!Without doubt, these are the best headphones ever heard although not the first to be of a professional audio standard. There was unsatisfied expectation that there may be an individual performance print-out of the actual unit's audio spectrum, distortion levels etc to demonstrate just how closely the two ear units matched; a similar chart was provided with professional 'phones purchased in the '70s and binned when its gel-filled, non-replaceable ear-cushions solidified over several months one summer.

Previously I had been a big fan of closed headphones but unless you pay quite a lot more than this Sennheiser 660S, you don't get the same quality sound for a closed headphone. This is strictly in-home audiophile listening. Let me at the outset say which genres of music it does well Techno, Funk, Classical and Jazz are amazing. Rock / Blues/ soul it passes muster. Pairing with a DAC improves the presentation but other headphones could also claim the same. I used it with two British DACS ( Chord Hugo) and IFI Hip DAC. Both the DACS significantly improved the reproduction and allowed the 660s to demonstrate its chops.The sound reproduction is Neutral. Bass is very good, consistent, and the mid-range is well-balanced and clear. Treble is ok and achieves good harmonic balance. Bass could be a bit more but as Sennheiser has pitched this headphone as an audiophile product ( quite a few hundred pounds below their flagship HD820) this does what it says with aplomb. Low levels of distortion, when paired with an appropriate amplifier, are also evident and continues into the high-level ranges. This is where these headphones shine, especially in the low bass range, where almost all competitors at this price point reach their limits more easily.There are no electrical tricks such as noise cancellation or sound processing. There is no Bluetooth and when it comes to Hi-resolution playback it delivers - in spades. Comfort is good, not great as I found it tightly clamped onto my head but was not tiring, though I am unlikely to wear these all day as I would do similar priced Japanese brands.It will show up shortcomings of poor recordings and therefore if you feed it quality stuff you will get quality listening experience. Sennheiser has provided a decent length of cable and connectors and adaptors, including:4.4-mm balanced Pentaconn and 6.35-mm connectivity (3.5-mm adapter supplied)Detachable cable with a 6.35-mm connectorDetachable cable with a balanced Pentaconn connector.In summary, this is a worthy successor to HD 650 and offers much in the way that you could expect from the higher-priced HD820 ( though that is a big step above). This 660S is also a significant step up from the HD 560 which I trialled but rejected as it did not handle Hi res sources all the well. For in-home listening and in-home listening only, this is one of the best in the market.