Sennheiser HiRes Audiophile Headphone (HD 660 S)

Product Information

The HD 660S comes in at an impedance of 150ohms and a sensitivity of 104dB. I personally found them to have plenty of volume on most devices I tested, like my MacBook Air and Nintendo Switch. However, I did think that they sounded better when being fed power from my amplifier. When running them on devices without a discrete amplifier I thought that they sounded a little more compressed, so I will list an amplifier as recommended for these. Still, these are very efficient, so it does not have to be a very powerful amplifier. Amplifiers like the Liquid Spark and JDS Labs Atom will be more than enough to drive these very cleanly.

When it comes to sound density, all 3 models are effortless. The sensation of a meaty sound, full of substance and density is best present on the HD 650 and HD 660 S. Starting with the bass of HD660S, it is a clear, clean and snappy bass. It has excellent speed and clarity, but it is not a basshead oriented bass. It has enough speed to make you tap your feet, it has enough body to give music an interesting presentation, but it isn't quite a lot in amount, being quite close to what would be considered a neutral bass. This is not something negative in any way, and in fact, it could be considered a strong point of HD660S, but it should be noted that if you're craving large amounts of bass, there are headphones that provide much higher amounts of bass. As a whole, the frequency response appear to be the most correct and complete on the HD 660 S. Yes, they’re a little more neutral from the midrange upward, but they never sound boring for their price category. The uild quality includes mostly plastic, Sennheiser HD660S has some other materials that are not plastic, like for example the drivers, or the grills on the drivers / the padding, but this shouldn't be taken negatively, since there are plastics that can resist to extreme amounts of weight and pressure.During my time with them, post the slight bending, I had no issues with having them on my head and listening to them for several hours without any fatigue. They stayed firm in place regardless of my lying position and truthfully, I really enjoyed how they felt on my head (again post bending [which again I stress to do at your own risk]). Perhaps time will break these into the forming sand the HD650 is to me but even if it doesn’t, what’s so wrong with the loving brace of a relative who really misses you? I'll not wax poetic this time regarding the long and storied history and my experiences with the HD 6xx family of Sennheiser headphones. For that, simply go have a look at my " The Very Important Sennheiser HD 580, HD 600, and HD 650" review.

The HD 660 S features a new transducer design developed by Sennheiser. This results in improved control of the diaphragm movements thanks to a specially manufactured precision stainless steel fabric, which is adapted to the contour of the diaphragm. Extremely light aluminum voice coils ensure the highest impulse fidelity. The transducers are carefully selected and paired by hand to ensure consistently narrow (±1 dB) tolerances. Sennheiser HD660S + Burson Play - Burson Play is a great little device created by Burson, a rather loved and well-known company. Play is most an Audiophile-Grade, modular, integrable DAC/AMP for desktop, and especially for desktop PCs. Its power is quite fit for HD660S, and it is a good way to prove that HD660S can sound pretty sweet on a proper desktop-class setup. The beauty of Burson Play comes from the fact that you can integrate it in your PC setup, so you can plug HD660S, or any other audiophile-grade headphone, directly in your battle station, and just enjoy audiophile-grade sound without having more devices on your desk or table. The sonic performance is quite variable with Burson Play, as it allows the user to change its OP-AMPs, but the most basic configuration offers a warm and smooth sound, with a pretty good soundstage, which pairs well with HD660S. Unlike the Momentum series, which has punchy sub-bass as its calling card, the HD 660 S have tightly-controlled bass. The frequencies are there, but so is the reserve expected of a higher-end headphone. To make up for this, the headphones delivers a little more power from fairly up-front mids.And where several of my more aggressively noisy test staples – Metz’s Strange Peace album, for one – become strident and wearing on the HD 580 Precision, the HD 660 S’ more forward mid-range and tighter bass make it possible to listen to the entire album from start to finish without reaching for a pair of earplugs. There’s enough clarity to separate the rolling waves of guitar distortion and clattering drums, and even the brash, overdriven drum and bass of Current Value’s Bigger Picture manages to bounce along excitedly without ever veering too far into harshness. Of course, this may not be best for all users since weight can add to the feeling of rigidness and reliability of a product, but still, it is impressive that Sennheiser managed to pull this off.

Moving down the headband still features it very nice and firm size adjustments that leave no doubts to the user what the cups have moved to a different size, for each adjustment is made with a notable pop. On that note, this headphone has more adjustment sizes than I think anyone will need. Unless you’ve a really tiny head, you’re more than likely to find the optimum adjustment out of this headphone.The padding in the new HD660 S feel very firm to the touch and offer a really nice level of both give and support. This may be because these are a brand new pair and my HD650 is, how should I say, well experienced, the padding looks to be a little bit deeper than my ol faithful HD650. This is a good thing because my ears no longer touch and rub against the cloth covering the drivers. The comfortable soundstage and detailed imaging hasn’t changed much. This was kinda difficult to determine because the forwardness of the mids and upper bass makes the soundstage sound a bit closer than the original HD650 did but when playing normal classical/instrumental music, at least me personally, I can’t hear a notable difference between the two in the soundstage and detail side of things. What I enjoyed immediately after switching to the HD600 was this sense of depth the sound gained over the HD660S. While the newer headphone is punchier and more impactful, it can sound thin and strident compared to the HD600. Now with enhanced bass depth, the fan-favourite Sennheiser HD 660S2 headphones have a more impressive all-round sound than ever.

These headphones are a follow-up to the Sennheiser HD 650, considered a classic pair for well over a decade now. Sennheiser retains the warm, accessible tone for the HD 660 S, making this pair easy to recommend to virtually anyone who can afford the high price. Prices valid in stores (all including VAT) until close of business on 29th November 2023. (Some of these web prices are cheaper than in-store, so please mention that you've seen these offers online.) Disclaimer: The Sennheiser HD 660S2 was sent to us by the local Sennheiser press agency in exchange for this review. Sennheiser is not related to Headfonia in any way. Maybe if you like a more lazy, relaxed and less dynamic sound with less detail, then yes, the HD 650 can bring exactly this to the table. For now it's sufficient to state that the Sennheiser HD 600 and HD 650 are probably the most highly regarded enthusiast headphone in the world, and I highly recommend both. The HD 650 is a bit too warm sounding for me (just a bit), and the HD 600 is my favorite of the two.I now realize that none of the models in the HD 6xx series, including HD 660 S, offers a convincingly large and expanded enough soundstage. The soundstage is somewhat compact and intimate, but surely not claustrophobic. I would categorize it as a medium-sized soundstage, not too large (like HD 800), but also not so close as to make me feel on the stage with the band. The sub-bass though sometimes leaves to be desired. The sensible use of an equalizer can solve the problem, but I don’t recommend adding more than 4-5dB in this area because the driver can start clipping and distorting when the volume is pushed above a certain point. The official price seems correct, exactly the price of the HD 650 14 years ago. If we factor in for inflation, they can be considered cheap for the current year. The bass of the HD600 is the most muted of the three headphones and it remains largely in its own camp and doesn’t intrude like the HD650 can at times. There is still a heft in the low end of the headphone that doesn’t completely eliminate the sensation of bass, but it’s hardly ideal for genres dependent on slam and rumble – for which the HD660S is a better choice. Overall impact is also less frantic than the HD660S, but seems slightly more pronounced than the HD650. The sub-bass rumble in Why So Serious? is also weaker and less controlled than the HD660S, but the instrumental has a certain sheen around it that is interesting. It’s not smoothed, like the HD650, but it’s definitely a softer and less harsh experience than the HD660S during the crashing moments. If you carefully listen to fast electronic music on the HD 650 or HD 600, you can hear a micro-echo, like an unpleasant resonance, maybe and effect of the over-damping behind the diaphragm (again just a guess). This effect damages the delimitation of notes and each individual sound end up not being sufficiently well defined.