Sennheiser HD 660 S
The Sennheiser HD 660 S is a new headphone from Sennheiser of the long running and widely praised HD 6xx family of headphones and is posited as an successor to the famed Sennheiser HD 650. The headphone retails at $499.95 USD which is the same MSRP as the HD 650, though the HD 650 can be found at around $300 new. As I don't have an HD 650 or HD 600 on hand any comparisons made between the HD 660 S and it's older siblings will be mostly from memory as direct comparisons have been brief, so I can't say for sure which I think is the best, but I can gather general tonal differences. I have heard all three at length on my system though and can say which I enjoyed the most on the said system. The system used on this review is a Sony UDA-1 connected to my desktop computer via USB and optical. The Sony UDA-1 is a system that leans on the darker and fuller side with rather strong bass dynamics. The amp/dac unit pairs well with the HD 660 S in my opinion. I spent a bit over a month heavily using these headphones to help reduce or eliminate any honeymoon period of initial hype to help make this review more fair and balanced. This review will reflect my long-term impressions of them.
Packaging/Accessories:
The packaging of the HD 660 S is pretty much exactly the same as the HD 600/650, same hinged cardboard box and very similar box design in which it says "The Legend Continues". Accessory wise it's pretty much the same as the HD 650 using what appears to be the same cable except it has an additional cable with a 4.4 pentaconn balanced connector.
Build/Durability:
The build quality of the HD 660 S is pretty much exactly the same as the HD 600 and the HD 650 except the finish is a bit different with a matte black finish without the glossy paint found on both the HD 600 and HD 650 and the different grill which is recessed a bit towards the rear and has the Sennheiser logo raised on both earcups, I found feeling for the Sennheiser logos makes it easier to determine which way to wear the headphones by feel alone. The build materials of the HD 660 S compared to other headphones in it's price range do feel a little on the cheaper side, but these materials do contribute to how lightweight the headphone is and with the HD 580, 600, and 650 have been proven to be very durable. There are no creaks, rattles, or squeaks with the headphone. Using the tried and tested design of previous HD 6xx family headphones, this is a headphone that is going to last decades if taken care of.
Comfort:
Comfort of the HD 660 S is exactly the same as the HD 650 and marginally different than the HD 600(different headband padding). Like all headphones in the HD 6xx family, the clamp is strong out of the box and the pads a bit stiff, this can cause some comfort issues initially to many due to how strong the clamp is. Many people bend the headband or the metal headband adjusters to help relieve the discomfort. I personally don't do either, I either just wear the headphones to let the headphone clamp and pads naturally break in or stretch them out on a series of books slightly wider than my head to help break them in more naturally.
Burn-in:
While burn-in is often a controversial topic among audiophiles, it is something I personally think happens. The HD 660 S just as with the HD 600 and HD 650 are headphones I find do have a rather long burn-in period. The HD 6xx family are headphones that are very sensitive to pad wear, the difference between new, moderately worn, and heavily worn pads is dramatic. The headphones tend to become warmer and more mid-focused the more pad wear there is based on past experience with the HD 600 and HD 650. I find the combination of pad wear, clamping pressure change, driver burn-in, and adjusting to the sound makes these headphones a bit on the slower side to fully break-in. For me personally the HD 660 S like the HD 600 and HD 650 was a headphone that took around 3 weeks of rather heavy use(3-4+ hours a day) to fully break-in and to fully appreciate and grasp.
Drivability:
The HD 660 S is an easier to drive headphone than both the HD 600 and HD 650 due to it's lower impedance at 150 ohms, though like the HD 600/650 it does appear to have a raise in the impedance that goes up to around 400 ohms where the HD 600/650 go up to around 600 ohms. This makes the HD 660 S an easier headphone to drive properly and much more friendly with a variety of different amplifiers. In terms of drivability I found the HD 660 S similar to Beyerdynamic's 250 ohm Tesla drivers. The HD 660 S uses what appears to be HD 700 derived drivers but the drivers themselves are likely tuned differently. I've only heard the HD 700 briefly a while back so I can't make any comparisons of the HD 660 S and the HD 700.
Sound:
Now to the most important aspect of this review, the sound. How does the HD 660 S sound? And is it an HD 650 successor or something else altogether? Well honestly it's a bit of both, it's not a full successor to the HD 650 as its sound signature is a bit different and it's also not dramatically different. This is definitely an HD 6xx series headphone sonically but it also has a few sonic differences to it compared to the rest of the family, it's a bit of an evolution and change from the rest of the HD 6xx family but a rather conservative change. Personally this is my favorite of this family of headphones for two main reasons. First, I find the HD 660 S to have more dynamic energy than it's older siblings and second I find the headphone more musically enjoyable across a wider variety of genres/uses. This is personally important for me as I have an eclectic taste in music and I use headphones for gaming, movies, and tv shows. I like my headphones to be universally good for all applications as I don't use headphones for only a select few uses. I like to use different headphones for different moods rather than for different genres or applications.
In this section I will be making some sonic comparisons to my other open-back headphone that is in a similar price range, the Beyerdynamic Amiron Home. The HD 660 S and Amiron are very different sounding headphones and which one will prefer is personal preference. I personally find the two headphones excellent complimentary headphones. Many people will likely be considering these two headphones against each other as potential purchases, so I decided to add this to the review. Both headphones are very comfortable. The Amiron does have nicer feeling materials and more metal in it's design, it's also heavier and has a much looser clamp. Both are very modular and both have removable dual-entry cables. Durability wise, the Amiron Home uses a relatively new driver design that are swappable without soldering like the HD 6xx family that first appeared in the DT 1770. I see the cable connecting to the drivers as a potential weak point on the Beyers, due to this I'll give durability to the HD 660 S overall. Also something to note, my personal sound preferences tend to lie a little more towards Beyerdynamics than Sennheisers overall.
Bass:
In terms of bass, this headphone is very much an HD 6xx series headphone but there are a few differences. The headphone definitely has a present mid and upper bass and the HD 660 S definitely has that thick and full sounding HD 6xx series sound. First this headphones seems to be a bit cleaner and extends a little bit deeper in the bass than the HD 650. Second the bass has a bit more slam and dynamic punch and it appears to have slightly more detail, it's not quite as present or warm as the HD 650, but I find the HD 660 S bass is of higher quality than it's predecessor. The bass is completely satisfactory to me, even though it does roll-off a bit early compared to what I'm used to. The bass like the HD 600 and HD 650 does roll off a bit early making the sub-bass not quite as present as some other headphones.
Compared to the Amiron Home; the Amiron Home has a cleaner, more detailed, and deeper reaching bass with more sub-bass presence. The Amiron doesn't really roll-off much at all bass-wise. The sub-bass on the Amiron Home can really get going on certain tracks. The bass focus on the Amiron is more in the sub-bass and mid-bass compared to the HD 660 S which is a bit more upper/upper-mid bass focused in comparison. The Amiron does sound a little lean in the upper bass compared to the HD 660 S. This helps gives the HD 660 S a thicker and fuller sound than the Amiron Home. The Amiron Home on the other hand seems to have a more solid backbone and foundation to it's sound partly due to it's stronger sub-bass presence. I like the Amiron's bass more overall.
Midrange:
The midrange of the HD 660 S. For me this is where I find the HD 660 S and all of the HD 6xx family to shine and is a big reason outside of the treble this family of headphones is so beloved by so many. The midrange of the HD 660 S is full, present, intimate, and has a very nice tonal richness to it that doesn't really seem to be found in headphones outside the HD 6xx series. It's a headphone that has a tendency to make other headphones sound a bit lean, recessed, and/or lacking richness in this region. The midrange of the HD 660 S is very even and doesn't seem to have any dips or raises, this makes the headphone sound very neutral and natural in this region. This is much of what makes an HD 6xx headphone an HD 6xx headphone. Tonally the HD 660 S nails it for me, it's very natural sounding and is just so right. Compared to the HD 650, I find the HD 660 S to be a bit more present in the upper midrange with a bit more in the presence region, more akin to the HD 600. Personally I find this a good thing as it makes the HD 660 S sound a bit more natural to my ears than the HD 650 did. Like all headphones in the HD 6xx family the soundstage is quite intimate and isn't very spacious or airy like some other open-backs can be.
Compared to the Amiron Home; the Amiron Home comes across as less thick and more spacious, like you are a few seats back away from the singer compared to the HD 660 S. The Beyers midrange is cooler sounding and comes across as a bit more delicate sounding. Vocals and instruments have a nice body and presence to them on the Amiron and the dynamics are excellent. Vocals and instruments on the HD 660 S have more authority and have a nice fullness, warmth, and thickness not found on the Beyers. The upper midrange can come across as a bit too forward to me at times, a similar thing I experienced in the HD 600 and the DT 1990. Nothing like the K712 or even worse the Q701 which can be way too forward at times. Vocals and instruments often come across as having more force on Senns which does help vocal clarity to be a bit better on the HD 660 S overall. I find it slightly easier to understand what is being said vocally on the HD 660 S compared to the Amiron Home. Vocals and the midrange of the HD 660 S is sligthly more to my liking. Tonally both headphones are excellent in the midrange
Treble:
The treble of the HD 660 S is in my opinion truly excellent. The treble is another reason this family of headphones is so loved, it takes a step back, is very clean without any peaks or sharpness, this allows for truly excellent vocal clarity as there isn't any excess sibilants masking the vocals on these headphones. It's very clean and honestly I find it of higher quality to my ears than the HD 600 and HD 650, it just comes off as a bit cleaner to my ears and seems to extend slightly more. The treble isn't harsh in the slightest. Like the HD 600 and HD 650 I do find it does roll-off a bit early, which some may refer to as a veil, but I honestly never really found any of these headphones veiled as I always found their clarity excellent. Compared to the HD 650 I do find the HD 660 S is on the brighter side and has a slightly different presentation with a bit more treble dynamics than what is found on the HD 650. I personally find the treble a welcome change in this headphone as I find it has more of the presence found on the HD 600 but cleaner and less fatiguing to my ears.
Compared to the Amiron Home; this is one of the most interesting comparisons between the two headphones. The treble presentation between the HD 660 S and Amiron Home is very different. The treble on the Amiron Home has a more vivid and dynamic character to it and more brightness in the upper treble than the HD 660 S. The Amiron does extend up higher in the treble, the combination of the more present upper treble and the greater treble extension on the Amiron can make the HD 660 S sound like it's missing a bit of information in the treble at times. The treble on the Amiron does have more bite. Instruments or vocals that rely on a clean and extended treble response sound great on the Amiron. Neither headphone is perfect in this area, the HD 660 S rolls off a touch too early and the Amiron Home has a bit too much upper treble energy. Overall I find the treble quality better on the Amiron Home despite having some extra upper treble energy. Neither headphone bothers or fatigues me treble wise even on tracks with problematic treble or are overly compressed(e.g., old youtube videos). The HD 660 S is more forgiving in the treble than the Amiron Home.
Imaging/Detail/Speed/Transparency:
The soundstage and imaging of the HD 660 S is very similar to the rest of the HD 6xx family, this gives me the impressions it's the housing that largely shapes this headphones imaging and soundstaging properties. The soundstage on the HD 660 S is on the narrow and intimate side, it has decent width but isn't what I call a very wide sounding headphone. The soundstage does carry a bit of that 3-blob effect which is a left, middle, and right focus with a break between the three areas. Listening to tracks where things pan left to right can show this as there can be a bit of a break, especially if it moves quickly from left to right like it can say on certain binaural recordings. I find this is situational and only manifests in certain tracks that use a lot of left-right panning. This may change a bit if balanced or on different systems, I'm not sure and I haven't confirmed/tested this. Despite the 3-blob quirk, the imaging is quite excellent and each sound is properly represented and clearly defined. It's imaging quality is what I expect from a headphone of this price range.
Detail wise, I find the HD 660 S very good and it divulges minute background detail and the detail of the vocals/instruments quite well, it's especially good in the midrange band of the sound. Since I haven't compared the HD 660 S and HD 600/650 at length I'm not 100% certain about detail levels in comparison. The HD 6xx family is a headphone series that often has an reputation of being slow, I never really found that the case with this series and the HD 660 S is no exception. While not really fast, it's also not slow either and keeps up with more complicated tracks with no issue. It's faster than I recall the HD 600 being. Not sure about the HD 650 as I found the HD 650 faster than the HD 600 as well.
Transparency is what I personally view as how well does the headphone disappear and get out of the way with music. The easier you can forget your listening to a headphone the more transparent it is. I find this is tied to the immersion factor, the more transparent the headphone is the more immersive it is. Like all of the HD 6xx family, the HD 660 S is a very transparent and immersive headphone, but not completely transparent as there is some grain in the sound.
Compared to the Amiron Home; in terms of soundstaging and imaging the Amiron has the upper hand, the soundscape on the Amiron is much larger and there is no 3-blob effect, left-right panning is fully cohesive all the time. Detail wise, that's a bit harder to say as I find the HD 660 S seems to have slightly more detail or the impression of slightly more detail in the midrange band but the Amiron appears to have more detail in the bass and treble. Both headphones are excellent in terms of dynamic slam and range. In terms of transparency, the Amiron is slightly more transparent. In terms of speed, the Amiron Home is a faster headphone, it handles more complex passages with greater ease than the HD 660 S. My system could possibly be holding both headphones back a bit in some ways.
Conclusion:
Overall I find the HD 660 S an excellent headphone, it's definitely an HD 6xx family headphone but it's a bit different due to it being much easier to drive, less amp finicky, and more dynamically lively than it's predecessors. Compared to headphones I've owned, the HD 660 S reminds me a bit of a mix of both the HD 600 and 650 and the DT 1990 with balanced pads. It seems to blend the sound signatures of the of the HD 600 and the HD 650 together and takes some aspects of the DT 1990 such as it's dynamic livliness and euphony(what I refer to as a certain hard to describe addictive almost sweet quality to the sound). Personally I highly recommend the HD 660 S, especially to those who are new to the HD 6xx family, want something more dynamically lively, something easier to drive/less amp finicky, and/or always wanted a little something extra/different from the HD 600/650.
I actually like the sound of the HD 660 S a little more than the Beyerdynamic DT 1990 Pro(which I prefer over both the HD 600 and HD 650) partly due to the HD 660 S richer midrange band, less dry sound, and smoother treble than the DT 1990 and I like the HD 660 S sound almost as much as the Amiron Home's. To me the HD 660 S is worth the price as I like it essentially just as much as the Amiron Home, which is my favorite sub-$1000 headphone. Others may not find the HD 660 S worth it, and like the HD 600 or HD 650 more depending on personal preference and/or system synergy. If possible I suggest people listen to all three, but also I find the HD 660 S is a headphone that takes some time to fully realize itself, first impressions may not tell you the full story. I instinctively listen to the HD 660 S just as much as the Amiron, there is no forcing myself to listen to it and no trying to justify liking it like I did with some headphones in the past. I simply enjoy the headphone and like to swap between it and the Amiron on songs to hear the differences in presentation and experience a different experience on the same song or album.
*Disclaimer: This is a review unit provided by Sennheiser in return for an honest review.
**A link to a Spotify playlist of HD 660 S synergy songs. Thank you EvShrug. If someone wants me to try a song on the HD 660 S, Amiron Home, or both compared just ask and I'll try to offer my impression of the song. I'm not really the best at describing the songs as I've never really done it before.
The Sennheiser HD 660 S is a new headphone from Sennheiser of the long running and widely praised HD 6xx family of headphones and is posited as an successor to the famed Sennheiser HD 650. The headphone retails at $499.95 USD which is the same MSRP as the HD 650, though the HD 650 can be found at around $300 new. As I don't have an HD 650 or HD 600 on hand any comparisons made between the HD 660 S and it's older siblings will be mostly from memory as direct comparisons have been brief, so I can't say for sure which I think is the best, but I can gather general tonal differences. I have heard all three at length on my system though and can say which I enjoyed the most on the said system. The system used on this review is a Sony UDA-1 connected to my desktop computer via USB and optical. The Sony UDA-1 is a system that leans on the darker and fuller side with rather strong bass dynamics. The amp/dac unit pairs well with the HD 660 S in my opinion. I spent a bit over a month heavily using these headphones to help reduce or eliminate any honeymoon period of initial hype to help make this review more fair and balanced. This review will reflect my long-term impressions of them.
Packaging/Accessories:
The packaging of the HD 660 S is pretty much exactly the same as the HD 600/650, same hinged cardboard box and very similar box design in which it says "The Legend Continues". Accessory wise it's pretty much the same as the HD 650 using what appears to be the same cable except it has an additional cable with a 4.4 pentaconn balanced connector.
Build/Durability:
The build quality of the HD 660 S is pretty much exactly the same as the HD 600 and the HD 650 except the finish is a bit different with a matte black finish without the glossy paint found on both the HD 600 and HD 650 and the different grill which is recessed a bit towards the rear and has the Sennheiser logo raised on both earcups, I found feeling for the Sennheiser logos makes it easier to determine which way to wear the headphones by feel alone. The build materials of the HD 660 S compared to other headphones in it's price range do feel a little on the cheaper side, but these materials do contribute to how lightweight the headphone is and with the HD 580, 600, and 650 have been proven to be very durable. There are no creaks, rattles, or squeaks with the headphone. Using the tried and tested design of previous HD 6xx family headphones, this is a headphone that is going to last decades if taken care of.
Comfort:
Comfort of the HD 660 S is exactly the same as the HD 650 and marginally different than the HD 600(different headband padding). Like all headphones in the HD 6xx family, the clamp is strong out of the box and the pads a bit stiff, this can cause some comfort issues initially to many due to how strong the clamp is. Many people bend the headband or the metal headband adjusters to help relieve the discomfort. I personally don't do either, I either just wear the headphones to let the headphone clamp and pads naturally break in or stretch them out on a series of books slightly wider than my head to help break them in more naturally.
Burn-in:
While burn-in is often a controversial topic among audiophiles, it is something I personally think happens. The HD 660 S just as with the HD 600 and HD 650 are headphones I find do have a rather long burn-in period. The HD 6xx family are headphones that are very sensitive to pad wear, the difference between new, moderately worn, and heavily worn pads is dramatic. The headphones tend to become warmer and more mid-focused the more pad wear there is based on past experience with the HD 600 and HD 650. I find the combination of pad wear, clamping pressure change, driver burn-in, and adjusting to the sound makes these headphones a bit on the slower side to fully break-in. For me personally the HD 660 S like the HD 600 and HD 650 was a headphone that took around 3 weeks of rather heavy use(3-4+ hours a day) to fully break-in and to fully appreciate and grasp.
Drivability:
The HD 660 S is an easier to drive headphone than both the HD 600 and HD 650 due to it's lower impedance at 150 ohms, though like the HD 600/650 it does appear to have a raise in the impedance that goes up to around 400 ohms where the HD 600/650 go up to around 600 ohms. This makes the HD 660 S an easier headphone to drive properly and much more friendly with a variety of different amplifiers. In terms of drivability I found the HD 660 S similar to Beyerdynamic's 250 ohm Tesla drivers. The HD 660 S uses what appears to be HD 700 derived drivers but the drivers themselves are likely tuned differently. I've only heard the HD 700 briefly a while back so I can't make any comparisons of the HD 660 S and the HD 700.
Sound:
Now to the most important aspect of this review, the sound. How does the HD 660 S sound? And is it an HD 650 successor or something else altogether? Well honestly it's a bit of both, it's not a full successor to the HD 650 as its sound signature is a bit different and it's also not dramatically different. This is definitely an HD 6xx series headphone sonically but it also has a few sonic differences to it compared to the rest of the family, it's a bit of an evolution and change from the rest of the HD 6xx family but a rather conservative change. Personally this is my favorite of this family of headphones for two main reasons. First, I find the HD 660 S to have more dynamic energy than it's older siblings and second I find the headphone more musically enjoyable across a wider variety of genres/uses. This is personally important for me as I have an eclectic taste in music and I use headphones for gaming, movies, and tv shows. I like my headphones to be universally good for all applications as I don't use headphones for only a select few uses. I like to use different headphones for different moods rather than for different genres or applications.
In this section I will be making some sonic comparisons to my other open-back headphone that is in a similar price range, the Beyerdynamic Amiron Home. The HD 660 S and Amiron are very different sounding headphones and which one will prefer is personal preference. I personally find the two headphones excellent complimentary headphones. Many people will likely be considering these two headphones against each other as potential purchases, so I decided to add this to the review. Both headphones are very comfortable. The Amiron does have nicer feeling materials and more metal in it's design, it's also heavier and has a much looser clamp. Both are very modular and both have removable dual-entry cables. Durability wise, the Amiron Home uses a relatively new driver design that are swappable without soldering like the HD 6xx family that first appeared in the DT 1770. I see the cable connecting to the drivers as a potential weak point on the Beyers, due to this I'll give durability to the HD 660 S overall. Also something to note, my personal sound preferences tend to lie a little more towards Beyerdynamics than Sennheisers overall.
Bass:
In terms of bass, this headphone is very much an HD 6xx series headphone but there are a few differences. The headphone definitely has a present mid and upper bass and the HD 660 S definitely has that thick and full sounding HD 6xx series sound. First this headphones seems to be a bit cleaner and extends a little bit deeper in the bass than the HD 650. Second the bass has a bit more slam and dynamic punch and it appears to have slightly more detail, it's not quite as present or warm as the HD 650, but I find the HD 660 S bass is of higher quality than it's predecessor. The bass is completely satisfactory to me, even though it does roll-off a bit early compared to what I'm used to. The bass like the HD 600 and HD 650 does roll off a bit early making the sub-bass not quite as present as some other headphones.
Compared to the Amiron Home; the Amiron Home has a cleaner, more detailed, and deeper reaching bass with more sub-bass presence. The Amiron doesn't really roll-off much at all bass-wise. The sub-bass on the Amiron Home can really get going on certain tracks. The bass focus on the Amiron is more in the sub-bass and mid-bass compared to the HD 660 S which is a bit more upper/upper-mid bass focused in comparison. The Amiron does sound a little lean in the upper bass compared to the HD 660 S. This helps gives the HD 660 S a thicker and fuller sound than the Amiron Home. The Amiron Home on the other hand seems to have a more solid backbone and foundation to it's sound partly due to it's stronger sub-bass presence. I like the Amiron's bass more overall.
Midrange:
The midrange of the HD 660 S. For me this is where I find the HD 660 S and all of the HD 6xx family to shine and is a big reason outside of the treble this family of headphones is so beloved by so many. The midrange of the HD 660 S is full, present, intimate, and has a very nice tonal richness to it that doesn't really seem to be found in headphones outside the HD 6xx series. It's a headphone that has a tendency to make other headphones sound a bit lean, recessed, and/or lacking richness in this region. The midrange of the HD 660 S is very even and doesn't seem to have any dips or raises, this makes the headphone sound very neutral and natural in this region. This is much of what makes an HD 6xx headphone an HD 6xx headphone. Tonally the HD 660 S nails it for me, it's very natural sounding and is just so right. Compared to the HD 650, I find the HD 660 S to be a bit more present in the upper midrange with a bit more in the presence region, more akin to the HD 600. Personally I find this a good thing as it makes the HD 660 S sound a bit more natural to my ears than the HD 650 did. Like all headphones in the HD 6xx family the soundstage is quite intimate and isn't very spacious or airy like some other open-backs can be.
Compared to the Amiron Home; the Amiron Home comes across as less thick and more spacious, like you are a few seats back away from the singer compared to the HD 660 S. The Beyers midrange is cooler sounding and comes across as a bit more delicate sounding. Vocals and instruments have a nice body and presence to them on the Amiron and the dynamics are excellent. Vocals and instruments on the HD 660 S have more authority and have a nice fullness, warmth, and thickness not found on the Beyers. The upper midrange can come across as a bit too forward to me at times, a similar thing I experienced in the HD 600 and the DT 1990. Nothing like the K712 or even worse the Q701 which can be way too forward at times. Vocals and instruments often come across as having more force on Senns which does help vocal clarity to be a bit better on the HD 660 S overall. I find it slightly easier to understand what is being said vocally on the HD 660 S compared to the Amiron Home. Vocals and the midrange of the HD 660 S is sligthly more to my liking. Tonally both headphones are excellent in the midrange
Treble:
The treble of the HD 660 S is in my opinion truly excellent. The treble is another reason this family of headphones is so loved, it takes a step back, is very clean without any peaks or sharpness, this allows for truly excellent vocal clarity as there isn't any excess sibilants masking the vocals on these headphones. It's very clean and honestly I find it of higher quality to my ears than the HD 600 and HD 650, it just comes off as a bit cleaner to my ears and seems to extend slightly more. The treble isn't harsh in the slightest. Like the HD 600 and HD 650 I do find it does roll-off a bit early, which some may refer to as a veil, but I honestly never really found any of these headphones veiled as I always found their clarity excellent. Compared to the HD 650 I do find the HD 660 S is on the brighter side and has a slightly different presentation with a bit more treble dynamics than what is found on the HD 650. I personally find the treble a welcome change in this headphone as I find it has more of the presence found on the HD 600 but cleaner and less fatiguing to my ears.
Compared to the Amiron Home; this is one of the most interesting comparisons between the two headphones. The treble presentation between the HD 660 S and Amiron Home is very different. The treble on the Amiron Home has a more vivid and dynamic character to it and more brightness in the upper treble than the HD 660 S. The Amiron does extend up higher in the treble, the combination of the more present upper treble and the greater treble extension on the Amiron can make the HD 660 S sound like it's missing a bit of information in the treble at times. The treble on the Amiron does have more bite. Instruments or vocals that rely on a clean and extended treble response sound great on the Amiron. Neither headphone is perfect in this area, the HD 660 S rolls off a touch too early and the Amiron Home has a bit too much upper treble energy. Overall I find the treble quality better on the Amiron Home despite having some extra upper treble energy. Neither headphone bothers or fatigues me treble wise even on tracks with problematic treble or are overly compressed(e.g., old youtube videos). The HD 660 S is more forgiving in the treble than the Amiron Home.
Imaging/Detail/Speed/Transparency:
The soundstage and imaging of the HD 660 S is very similar to the rest of the HD 6xx family, this gives me the impressions it's the housing that largely shapes this headphones imaging and soundstaging properties. The soundstage on the HD 660 S is on the narrow and intimate side, it has decent width but isn't what I call a very wide sounding headphone. The soundstage does carry a bit of that 3-blob effect which is a left, middle, and right focus with a break between the three areas. Listening to tracks where things pan left to right can show this as there can be a bit of a break, especially if it moves quickly from left to right like it can say on certain binaural recordings. I find this is situational and only manifests in certain tracks that use a lot of left-right panning. This may change a bit if balanced or on different systems, I'm not sure and I haven't confirmed/tested this. Despite the 3-blob quirk, the imaging is quite excellent and each sound is properly represented and clearly defined. It's imaging quality is what I expect from a headphone of this price range.
Detail wise, I find the HD 660 S very good and it divulges minute background detail and the detail of the vocals/instruments quite well, it's especially good in the midrange band of the sound. Since I haven't compared the HD 660 S and HD 600/650 at length I'm not 100% certain about detail levels in comparison. The HD 6xx family is a headphone series that often has an reputation of being slow, I never really found that the case with this series and the HD 660 S is no exception. While not really fast, it's also not slow either and keeps up with more complicated tracks with no issue. It's faster than I recall the HD 600 being. Not sure about the HD 650 as I found the HD 650 faster than the HD 600 as well.
Transparency is what I personally view as how well does the headphone disappear and get out of the way with music. The easier you can forget your listening to a headphone the more transparent it is. I find this is tied to the immersion factor, the more transparent the headphone is the more immersive it is. Like all of the HD 6xx family, the HD 660 S is a very transparent and immersive headphone, but not completely transparent as there is some grain in the sound.
Compared to the Amiron Home; in terms of soundstaging and imaging the Amiron has the upper hand, the soundscape on the Amiron is much larger and there is no 3-blob effect, left-right panning is fully cohesive all the time. Detail wise, that's a bit harder to say as I find the HD 660 S seems to have slightly more detail or the impression of slightly more detail in the midrange band but the Amiron appears to have more detail in the bass and treble. Both headphones are excellent in terms of dynamic slam and range. In terms of transparency, the Amiron is slightly more transparent. In terms of speed, the Amiron Home is a faster headphone, it handles more complex passages with greater ease than the HD 660 S. My system could possibly be holding both headphones back a bit in some ways.
Conclusion:
Overall I find the HD 660 S an excellent headphone, it's definitely an HD 6xx family headphone but it's a bit different due to it being much easier to drive, less amp finicky, and more dynamically lively than it's predecessors. Compared to headphones I've owned, the HD 660 S reminds me a bit of a mix of both the HD 600 and 650 and the DT 1990 with balanced pads. It seems to blend the sound signatures of the of the HD 600 and the HD 650 together and takes some aspects of the DT 1990 such as it's dynamic livliness and euphony(what I refer to as a certain hard to describe addictive almost sweet quality to the sound). Personally I highly recommend the HD 660 S, especially to those who are new to the HD 6xx family, want something more dynamically lively, something easier to drive/less amp finicky, and/or always wanted a little something extra/different from the HD 600/650.
I actually like the sound of the HD 660 S a little more than the Beyerdynamic DT 1990 Pro(which I prefer over both the HD 600 and HD 650) partly due to the HD 660 S richer midrange band, less dry sound, and smoother treble than the DT 1990 and I like the HD 660 S sound almost as much as the Amiron Home's. To me the HD 660 S is worth the price as I like it essentially just as much as the Amiron Home, which is my favorite sub-$1000 headphone. Others may not find the HD 660 S worth it, and like the HD 600 or HD 650 more depending on personal preference and/or system synergy. If possible I suggest people listen to all three, but also I find the HD 660 S is a headphone that takes some time to fully realize itself, first impressions may not tell you the full story. I instinctively listen to the HD 660 S just as much as the Amiron, there is no forcing myself to listen to it and no trying to justify liking it like I did with some headphones in the past. I simply enjoy the headphone and like to swap between it and the Amiron on songs to hear the differences in presentation and experience a different experience on the same song or album.
*Disclaimer: This is a review unit provided by Sennheiser in return for an honest review.
**A link to a Spotify playlist of HD 660 S synergy songs. Thank you EvShrug. If someone wants me to try a song on the HD 660 S, Amiron Home, or both compared just ask and I'll try to offer my impression of the song. I'm not really the best at describing the songs as I've never really done it before.
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