The Sennheiser HD 660S2 sounds delightful
10/8/2023
Translation: Patrik Stainbrook
The classic brand has brought out a new hi-fi headset following the old motto: no frills. Despite the open design, it apparently packs a powerful bass.
The Sennheiser HD 660S2 is an old-school over-ear headphone. No Bluetooth, no built-in amplifier, no noise cancelling, no phone features. So it manages without a battery. Besides, it is an open headphone. Unfiltered sound penetrates the headset in both directions. This has pros and cons, as I explored further in the article below.
These headphones are even more open than others. Apart from a fine metal grille, nothing separates the speaker from its surroundings. The inner workings are fully visible.
Source: David Lee
Cables and ports
Sennheiser – or, the new brand owner Sonova – supplies two cables. This also makes it clear that the cable can be easily replaced. There’s a socket on each shell, securing the connection while still easy to remove.
One cable ends as an ordinary 6.3 mm jack plug. An adapter to 3.5 mm plugs, also included, can be hooked on. The adapter has a short cable, keeping the link small and less likely to bend. A detail I like.
Source: David Lee
The second cable has a 4.4 mm plug. It allows for a balanced connection with a suitable source device (article in German). In the process, interference and buzzing noises are reduced to an absolute minimum. At a rather short 1.8 metres, audible noise shouldn’t occur anyway. I can’t test the balanced connection as I don’t have a suitable DAC. However, there are quite affordable models from FiiO for both mobile and stationary use.
First listen impressions
As the suffix «2» indicates, this is the successor to the Sennheiser HD 660S. The new edition primarily looks to offer a stronger bass, but otherwise has a similar sound. This despite the fact that the speaker’s diameter of 38 mm is slightly smaller than the predecessor’s (42 mm).
I can’t compare the two Sennheiser models since I only have the S2. For comparison, I instead draw on my own open headphones, the Beyerdynamic DT 990 Pro.
Sennheiser’s headphones are clearly louder, doubly confirmed to me by the specs: 104 dB vs. 96 dB. This is despite higher impedance, 300 ohms for the Sennheiser model and 250 ohms for the Beyerdynamic headphones. This value has doubled compared to the predecessor and is too high for use with a smartphone or other weak mobile devices. You can hear something, but it doesn’t sound strong or good in any way.
The varying volume levels of the two open headphones don’t make a direct comparison very easy. Still, I’m sure the Sennheiser HD 660S2 is less treble heavy than the Beyerdynamic DT 990 Pro right off the bat. The bass also has more power – but it’s mainly with the trebles that the difference shows.
However, the bass doesn’t seem too loud at all. This is rarely the case with open headphones. Anyway, it usually isn’t the volume that’s annoying. The bass is off too often. That luckily doesn’t happen here.
By the way: I didn’t know the current model is supposed to have a stronger bass when doing my test. I try to be as impartial as possible initially, as expectations strongly influence the testing experience.
Measurements
Using the miniDSP Ears measuring device, I capture the volume of different frequencies. Regarding the highs, the result confirms my first impression. They’re less accentuated on the Sennheiser HD660S2 than on the Beyerdynamic model. In the low bass range, however, the measurement contradicts my impression. According to the values, the Sennheiser headphones are quieter there as well.
Source: David Lee
My values should be correct, as measurements made by portal Rtings.com also show less bass in the Sennheiser model when compared.
I measured five times per channel and there was little variation. Unlike many closed headphones, the bass hardly changes depending on how the headphones rest on the head.
My second go-around
Another sound test is in order. This time I make sure by measuring that both headphones play the control tone of 300 Hz equally loud. Now, it initially feels like the bass is quieter on the Sennheiser. However, the rest of the music also seems a bit quieter. It’s why I turned the Sennheiser headphones up too high intuitively. Perhaps the basses also seem louder than they are because kick basses seem more explosive than on the Beyerdynamic DT 990 Pro. That’s my subjective impression, at least.
All in all, the sound is warm and pleasant, not razor-sharp. I consider this a plus when listening to music for a long time. My ears don’t tire as quickly.
Warm doesn’t mean muddy, mind you. Individual instruments are easy to pick out. The left-right spectrum is extremely clear. If the hi-hat or any other bright percussive instrument is at the far left or right edge of the stereo spectrum, it even feels too far out. But that’s probably just me being weird.
Wearing comfort
The headband can’t be adjusted steplessly, but it can be expanded very far. The Sennheiser HD660 S2 should fit pretty much any adult head. However, the pressure may be too strong for large heads. I found it slightly unpleasant at first, but quickly got used to it. The fabric feels comfortable and its 260 grammes are hardly noticeable. They’re also well padded at the top of the headband.
Source: David Lee
Verdict: sounds good, but the bass isn’t revolutionary
The Sennheiser HD 660S2 delivers a balanced sound – warm and pleasant, yet precise. The manufacturer states a significantly more powerful bass as the most important improvement compared to the predecessor. However, the HD 660S2 still can’t manage a truly impressive bass. Not even for an open headphone. If you’re primarily looking for headphones with strong bass, you won’t find them here.
You’ll be just as disappointed with this model if you want something for on the go. The impedance is unsuitable for smartphones and similar devices, and the open design is annoying in loud environments. The HD 660S2 is meant for quiet living rooms. It’ll certainly please many buyers in this respect.
David Lee
Senior Editor
David.Lee@digitecgalaxus.chMy interest in IT and writing landed me in tech journalism early on (2000). I want to know how we can use technology without being used. Outside of the office, I’m a keen musician who makes up for lacking talent with excessive enthusiasm.
