Sennheiser HD660S2 Measurements: The Clone Wars

Oh I see what you mean. Default HD600/650 don't really have super tight imaging and it gets worse over time when the pads squish. I think it's a general HD6xx design flaw to put your ears right up against the driver with so little distance and it's pretty hard for me to go back to stock pads after over a year of using @zach915m 's angled perf lambskin cause without the angling and sound "tunneling" it does the HD600/HD650 don't sound particularly directional and vibrant enough.

I think we praise the stock pads way too much when Axel Grell has gone on to say in a podcast that the pad squish sucks ass which led him to engineer ultrathin gasket-like pads for HD800 that just seal and can squish over time without affecting the sound too much:
https://theoccasionalpodcast.libsyn.com/axel-grell-designer-of-the-sennheiser-hd-600650800 15 minutes in

I really wish Sennheiser didn't completely lose the plot on timbre with the HD800 and especially HD700 cause I can see genuine technical upgrades in those compared to the 6xx line.

 

As someone who uses the HD600s with pads that are more decorative than functional (hyperbole) I feel like I actually much rather prefer the HD600 when my ears are right up against the baffle; I definitely hear a lot of things as being uncomfortably close (e.g. the vocals during the verses of that one Hayley Williams track I referenced in my impressions), but that actually just makes for better contrast against when things "open up" for the chorus-- by virtue of there being allowance for elements being very close to the listener on the illusory headstage, the perceived range of depth is thereby improved.



It's all preferences though, like how some folks really do just prefer DACs that throw a massive stage out where everything's just a wall of sound off in the distance. Personally I don't hear that as being "worse" imaging, but eh I am ready to concede that as much as I blab on here I'm less experienced with lots of gear compared to most of the forum still.

 

A trough in the low treble followed by a peak in the mid-treble seems to have become a Sennheiser signature in recent years. I haven't heard the HD 660S or S2, but from the comments here and the measurements in the first post (particularly the comparison to the HD 650, and to the JAR600 which goes the opposite way), the 660S2 seems to have that in common with a number of recent IEMs and with the HD 620S. With the 620S, I saw some discussion - which I can't now find - that it was an intentional ploy to increase the perceived immersiveness of the stage.

As a 'tone first' sort of guy: I disapprove

 

I can see that with the stock pads if you just make it sit the drivers further away since those are extremely leaky but the ZMF pads also shrink the opening size a bit to compensate for extra depth and perforated lambskin kinda glues to your face a bit which lowers side leakage, so the net effect is the driver sound is more "tunneled" into your ears, which combined with the slight angling really does sound both more spacious and focused at the same time, which to me reminds me more of Focals than the 660S2 which has a planar-ish vibe.

 

This reminds me of something I actually forgot about for a bit: my HD600s aren't stock. LMAO I'm running the 2019 driver assemblies in 2014 baffles because I liked the look of them more (again, more finished with less hasty machining marks left over), but also because I liked the greater low end volume that seemed to track with the older HD600 baffles-- the later drivers required quite a bit more force to dunk them into place in this configuration, which caused no shortage of shenanigans for a bit (some channel imbalance that later fixed itself somehow) but also seems like it's replicating some of this effect too. Maybe I should get a stock HD650 in to compare things to, a friend has one that I don't think they're using too often nowadays.

 

In that same podcast link Axel confirmed that the HD650 is indeed more closed than the HD600 in terms of acoustic impedance and the FR difference is just one consequence. 600 is quite audibly the cleanest treble followed by 650 with a bit of a blur and 660S2 which is hazy and strident at the same time. I do think HD650 while having the nicest balance of tone between all three is the weakest one technically since that bloom is quite annoying once your brain acclimates to the HD600 while the HD660S2 baffle actually has the damping chops to hold that energy, like a better braced box. But HD600 is cutting it close to being bright unless you got the right chain going into it, so it's giving some nervosa about source chain again even with BF2OG>SW51. Again, I think the more open HD600 combined with the better side seal of the ZMF pad is a pretty incredible synergy and am a total ZMF pad shill after a year of having them (and also not having my ears rub against the damn metal baffle is great for comfort).

 

Following up with a quick video of the finishing on the back of the HD660S2's baffle. The machining marks are at least a bit more polished-looking than what I remember of the newer HD600, but it's still less presentable (IMO) than on the slightly older HD600.

You can definitely see that quite a bit of care went into the damping, and yes I would hope that metal mesh proves more resilient than foam



Also, finally got around to taking some photos of the baffle rear with the new phone (my last one died of water damage cuz I suppose the ingress protection had worn down over the last few years, I'm pissed cuz this was an unexpected expense but hey "better" camera I suppose [I used an old watch loupe thing to help with focus]):






Plus a closeup of some of the tooling marks on the plastic that are absent on the 2014 HD600:

 

Those are some awesome shots. Yeah the HD660S2 driver mesh does look pretty incredible compared to the HD600's basic white backing paper, which they said was sourced from a filtering paper company. As for tooling marks, that might be due to Sennheiser having to hop around in terms of factories for the past decade from Ireland to Romania and then back to their new facility in Ireland. Despite all that, they run an absolutely tight ship.

As for sound, when I say the HD660S2 sounds larger I do mean it sounds like that entire metal mesh region including the ellipse around the driver sounds like it's moving together, so obviously they're doing something right. Still, I wish they would keep that mesh baffle tech to the chassis side and just do paper for drivers if it's what's causing these treble issues. Right now I'm still enjoying them before I have to return but that's with the specific synergy of ZX300 4.4mm balanced out on stock firmware cause the ZX300 rolled treble will trigger the 660S2 treble less.