Build Quality
Other than its predecessor, they are build out of plastic. This doesn't have to be bad. There is plastic and then there is plastic. My HD 580 Jubilee are also mostly made out of plastic and are still standing strong. I just hope, that the plastic used in the Momentum 4's can withstand sun exposure, because I'm mainly going to wear them out and about. Only time will tell.
Comfort
Coming from a pair of Sony XM3, the Momentum 4 are a step-down. They aren't uncomfortable, but could be better. The ear cups are on the smaller side. For my ears, it's barely big enough. The headband padding could be a bit firmer, or have more padding.
Bluetooth and Controls
The headphones got delivered with the newest firmware already installed. Which is a big plus. Connecting the headphones to my phone was as easy as it gets. The Android app also works without any problems. Only thing I don't like is the need to make an account for the custom EQ thing.
The touchpad works well, almost a little too well. Even the slightest touch pauses the music. The pinch gesture to change the ANC setting is a hit-and-miss. From ANC level 1 to neutral to transparency level 1 it works quite well, but either turning up the ANC level or transparency level above that needs a lot of tries.
ANC and Transparency
The ANC introduces a slight hiss, which is inaudible once music is playing. Other than that, it works great. On par with the Sony XM3. The transparency mode is a bit strange. Transparency mode turned all the way up produces a sound as if wind is blowing. Only that I'm inside with all the windows closed, and no AC turned on.
Sound
This is the strong point of these headphones. At home, I'm using a set of HD 580 Jubilee (predecessor of the famous HD 600) with a Fiio K5 Pro. The Momemtum 4 almost sound like a closed back version of the HD 580 Jubilee with slightly less pronounced mids and a sub bass extension.
Almost any of the Bluetooth headphones I tried out boost the lower mids/ upper bass. Hiphop sounds good, but everything else with drums (rock, metal) starts to sound muddy. This is even the case with the Momentum 3. I have no idea how Sennheiser managed to fix this with the Momentum 4, but they did. If the song has subbass, it's audible. If the song has strong subbass, the headphones have a subwoofer-like feeling to them. It does all that without convoluting the mids (or only ever so slightly). This also means that if a song has badly mixed bass, you're going to hear it.
Kickdrums in Metal songs lose a little tightness compared to my HD 580 Jubilee, but are fuller.
Mids are a tiny bit recessed. In The Seed by Aurora with the HD 580 Jubilee Aurora's voice is in the foreground. With the Momentum 4, it fights a bit with the low bass notes. But in return I hear bass notes, I can't hear with the HD 580 Jubilee.
Highs are nicely done too. They sound detailed without sounding harsh.
Imaging is superb. I am able to pinpoint the instruments with ease. I can even distinguish if something is coming from closer or further away.
Soundstage is good for a closed back headphone. It leans on the analytical side of things, which I like.
Final Thoughts
Sound wise, the Momentum 4 are the perfect match to my HD 580 Jubilee. Bass response is way better than 90% of other Bluetooth headphones in their price range (or even above) and are better than the Momentum 3. Comfort could be slightly better. All in all, a definitive recommendation for its price.
