UPDATE SEPTEMBER 2023I wrote a review comparing the Bang & Olufsen Beoplay HX against the Sennheiser Momentum 4. You can find it on my Amazon Profile.UPDATE AUGUST 2023The latest firmware update incorporates Snapdragon Sound with High Resolution Audio (96kHz sample rate) and a five-band EQ (the previous equaliser had three bands). Besides this, I've noticed a faster pairing to the Smart Control App.Be aware that firmware updates take quite some time (your headphones must be connected and close to your phone during this time). The App predicted 25 minutes in my case (Android 12), yet it got stuck when there were two minutes remaining. I left it overnight and on the next morning the App still said "2 minutes remaining". Hence, I forced quit the App and after reopening it, everything looked fine and refreshed (when checking for new updates, it also confirmed I was using the latest firmware update).Therefore, the firmware update process is long and a bit stressful with Sennheiser. It was the same with the previous update, though that time it didn't get stuck and the whole process lasted around 30 minutes. But, at the end, it works and the updates do improve the overall experience with the product.KEY POINTSWhen compared against the Sony WH-1000XM5 and the Bowers & Wilkins PX7 S2, the Sennheiser Momentum 4 has the best sound, comfort (with and without glasses) and battery life from the three.Sony has the best ANC and microphones for phone calls (especially in noisy environments).The PX7 S2 is only the best when it comes to luxurious build quality. At everything else, it is surpassed by either the WH-1000XM5 (ANC, Comfort, Calls) or the Momentum 4 (Sound, Comfort, Battery, Calls). Additionally, the wearing sensors and microphones for phone calls do not work as one would expect.WHY NOT SONY?Their carrying case is huge, there is no aptX support, one must sacrifice LDAC when applying any EQ, the headband is too thin, the build quality is not worth 419 EUR (you can’t even replace the ear pads), there is no USB-C Audio and their battery life is half of the Momentum 4s.WEAK POINTS (MOMENTUM 4)The ANC is not as effective as on the Sony WH-1000XM5. In fact, even the WH-1000XM3 has significantly better ANC than the Momentum 4.Additionally, it is not possible to turn the ANC off. On the other hand, if you are sensitive to strong levels of ANC (a feeling similar to riding a high-speed elevator), you are allowed to adjust the level of ANC manually (something you can't do on the Sony headphones).BATTERY LIFEThe Momentum 4 has around 30 hours more of battery life compared to the other two. The Sony’s might be the worse from the three if you plan to use LDAC, as this audio codec consumes a lot of battery, both from the headphones and your smartphone. On top of that, LDAC is way less stable when other interfering signals abound (e.g. airports and train stations). Regarding the PX7 S2, you will probably turn off the wearing sensors and, hence, its power-saving feature. So you might run out of juice before their advertised 30 hours if you forget to manually pause your music and/or turn them off.SOUNDBassThe Sony’s have an exaggerated bass across the board. In fact, the upper-bass bleeds without regrets into the low-mids. This generates a bloated sound that lacks definition. The Momentum 4 has elevated sub-bass only and the elevation recedes in the upper-bass before entering the midrange. This generates a cleaner sound that allows the midrange to be perceived more clearly. Therefore, you can hear more details in the mix that would otherwise be masked by the boomy high-bass. Although the Momentum 4 has too much sub-bass, in my opinion, you can easily fix this in the App EQ. Another good news for users of the Momentum 4 is that you will still preserve the high bitrate codec (aptX Adaptive) when using any EQ; Sony users will need to sacrifice LDAC if they wish to EQ the default sound profile of their headphones.The PX7 S2 has very little sub-bass, tons of mid-bass and a better transition into the midrange compared to the Sony’s. Therefore, it is not boomy like the Sony but it tends to sound “cluttered” when the music gets too complex (or if there is lots of bass); you feel that the space between instruments gets lost during these instances.MidrangeThe usual strength of open-back Sennheiser headphones has always been the midrange. The HD 600, 650 and 660S all boast a present, warm and linear midrange. This usually increases the resolution, as there are no dips in the sound frequency response. The Momentum 4 follows suit with a mainly linear midrange, especially when compared against the PX7 S2, where the midrange is clearly recessed. The Sony’s midrange is also linear, but it has the bleed-through from the high-bass, which muddies its overall performance.TrebleThe Sony WH-1000XM5 has a second issue in its sound: it has a sharp roll-off in the high-treble region that dampens the sound and takes out “air” from the music. This is perceived as a “dark” sound signature. Neither the Momentum 4 nor the PX7 S2 have this issue. However, the PX7 S2 has some clear “coloration” in its treble; there are some peaks either in the low-treble or mid-treble. Combined with its exaggerated mid-bass, the timbre of the PX7 S2 tends to sound a bit nasal and not as full as one would expect (it does not sound very natural, although it might sound more exciting on certain songs). The Momentum 4, once more, has the most natural sound when it comes to treble. It is not sibilant or piercing, it does not accentuate any particular region, but it also does not lack air and extends way better than the Sony’s.BUGS?I have not experienced any issues with my pair so far. They charge as expected, they turn on when I take them out of the case and turn off when I put them back inside (you can also turn them off manually). They do not turn on while inside the carrying case either (even when carrying them inside a backpack). The wearing sensors work perfectly fine and I have not experienced false pauses after more than five months of regular use.The Smart Control App looks nice, modern, and it has worked fine so far. However, firmware updates take a long time (around 25 minutes). During this time, your headphones must lay close to your smartphone. I never faced such time-consuming firmware updates with any other bluetooth pair before. This is something that will be an issue every time a new firmware update is available.ANCThe ANC on the Momentum 4 is definitely worse than on both my WH-1000XM3 and the WH-1000XM5. No doubts. It is very clear that Sony is ahead of the game in this category. I didn’t have the chance to try the ANC on the PX7 extensively, but for sure it was also worse than on both Sony headphones. The main issue on the Momentum 4s ANC is with high-frequency sounds; they are not blocked almost at all (even the passive noise isolation here is disappointing). Low-frequency noises, on the other hand, are cancelled out pretty good (the Sony's still perform better though).COMFORTExcellent. Together with the battery life, these two features deserve 5 stars. The headband design is by far the best. The Sony has the least amount of clamping force but its headband is too thin and does not distribute the pressure evenly. The PX7 S2 has a decent headband but its ear pads are stiffer (less soft) and generate pressure spots when wearing glasses.There is only one small downside to the Momentum 4s comfort: hot days. The synthetic leather on the ear pads is not breathable at all (it seems to be waterproof). This makes your skin sweat and it can be an issue during hot days. The only solution to this would be to implement real leather, which allows your skin to breathe.BUILD QUALITYThe Sony is the worst when it comes to build. It uses only plastic and you can’t replace the ear pads easily. The Momentum 4 uses more plastic than the PX7 S2, but the inner side of its headband is covered with silicone, which endures better against sweat than synthetic leather. This is a critical point because the inner part of the headband can’t be replaced on any of these three models. Additionally, the lifespan of these products is also determined by its internal sealed battery: the longer a battery lasts, the longer the product will last. Therefore, even though the PX7 S2 uses more metal and looks more premium, I am not sure it will last longer than the Momentum 4.CONCLUSIONI need to admit that I will miss the portability and ANC of my WH-1000XM3. Additionally, the stepless adjustment of the headband on the Momentum 4 is annoying because I must invest more time to find the proper seal (the clicks on the WH-1000XM3 made it super fast to know where to adjust the headband). Additionally, not being able to turn off the ANC is worrying. If some microphones start to malfunction at some point, I won’t be able to use the headphones to listen to music because I can’t deactivate the defective microphones.I do recommend the Momentum 4. They give you the best combination of sound, battery life, comfort and ANC within the 200-400 EUR price range. I do not see any reason to pay more for the competition. I will change my conclusion and rating if I experience any dramatic issues within the next two years. It is a clear winner unless your priority is ANC (WH-1000XM5).