By the standards of some Sennheiser headphones, the HD 660 is one of the more recent arrivals in the range. The original model appeared in 2018 and five years later, Sennheiser has taken it upon itself to create an S2 model. Considering that the similarly priced HD 650 has been unchanged in rather longer than this without any alterations at all, you might surmise that Sennheiser is still tinkering with the recipe. The new model is still an open back, full size over ear design that is recognisably the same as the older model but embodies a number of tweaks.
Some of these tweaks are quite considerable too and the most important concerns the driver. Most of the time when a headphone company updates the engine room of a headphone it results in the driver getting bigger but the reverse is true here. The HD 660S2 ditches the old 41mm unit for a smaller driver that is 38.5mm across. This represents a significant drop in the radiating area of the new headphone. Despite this, Sennheiser claims to have doubled the sub bass output of the smaller driver resulting in more low end than there was before. Some of this will be down to a new vented magnet system and aluminium voice coil improving the response.
The impedance of the HD 660S2 has been changed from 150 ohms in the older 660S to 300 ohms in the new one. This is now the same as the HD 650 and Sennheiser says this significantly improves the impulse response. Sennheiser goes on to say that the new headphone is more sensitive across the entire frequency response which is potentially useful as well if you are looking to partner them with less powerful headphone amps. Your choice of partnering equipment can be balanced or unbalanced too as the Sennheiser is supplied with two 1.8 metre long cables with 6.35mm and 4.4mm connections on them.
Sennheiser has long made play of their pro audio heritage and the HD 650 in particular has been a watchword for an accurate and neutral performance at a reasonable price. The HD 660S2 doesn’t radically move away from these ideals but it does tweak them slightly. Without becoming softer or less dynamic, this is a more forgiving headphone than it’s older sibling. It handles poorer recordings with a magnanimity that allows you listen and enjoy them for what they are. The boost in sensitivity helps too, giving the HD 660S2 an engaging lightness and immediacy. Tonal realism in particular is outstanding for a headphone at this sort of price and will keep some rather more expensive alternatives honest.
As an open back design, the Sennheiser doesn’t struggle to create sense of material not simply being jammed against the ear and this helps larger scale material in particular to sound open and unforced. Where the Sennheiser is less assured though is the ability to push information in front of the listener, although if you have a source with a crossfeed setting (or DSP that can achieve the same thing), it has proved responsive to that.
Perhaps more importantly though, the HD 660S2 is fun. Without interfering with the perception of accuracy, neutrality and a commendably deep and powerful bass response that integrates nicely with the upper registers, the Sennheiser manages to latch onto rhythms and time signatures and deliver them with real bite and attack. That driver might be smaller but it hits hard and moves with real urgency when it needs to. No less importantly, when you don’t need your headphone to go like the clappers, the Sennheiser slows up and lets the material flow as it should.
The basic design of the HD 660S2 is very similar to the long running HD 650 and this means that some of the same positives and negatives apply. In the positive column, this is a superbly made headphone for the price. It’s not the most ornate design going but absolutely everything feels solid and substantial and like it’s going to last for years. The design also has an excellent range of size adjustment too.
Unfortunately, like other similar Sennheiser designs, the pressure that the HD 660S2 exerts on the side of the head is quite high and combined with a the relatively unyielding foam padding it means that the Sennheiser is not as comfortable to wear for long periods as some similarly priced designs. The material finish on the pads themselves is commendably animal free but can become a little oppressive on hot days as well. It's definitely something you should try before you buy.
The last quirk of the Sennheiser concerns the connections. The unbalanced cable has a fixed 6.35mm jack with detachable 3.5mm adapter. On a £500 headphone this feels like the wrong way around as a great many devices it will be connected to will only have a 3.5mm connection available. Aftermarket options are available but they add to the overall cost.
The HD 660S2 isn’t completely perfect but the core offering here is very good indeed. What it does very effectively is blend accuracy and realism with just enough fun and forgiveness to ensure that even very diverse collections of music will be handled effortlessly. Throw in the solid build and finish and you have an excellent home headphone.
Sturgill Simpson Cuttin Grass Vol I.
One of the most beautiful group recordings of recent years, the Sennheiser imparts an energy and sheer joy to these bluegrass songs that firmly delivers on emotional enjoyment
Billy Joel The Stranger
The Sennheiser’s innate timing and energy ensures that every hook laden tune is infectiously entertaining. Of course, the detail on offer means you can hear all the iffy lyrics too but you can’t have everything
The monstrous low end on offer here is a stiff challenge for the Sennheiser’s 38mm driver but it rises to the challenge well, delivering low end shove, you can feel as well as hear and that still moves with impressive speed and agility.
If you need a home headphone and can work with their open back noise leakage, the Sennheiser offers a lot of bang for your buck and will work well even on fairly low powered headphone amps.