13/08/24 I received the Sennheiser Momentum 4 headphones. Aesthetically and functionally, they are impressive. The case for the headphones is convenient, and it is also hard for maximum protection of the product during travel. Although I haven't had them for a long time (not even a day), I can say that so far they work flawlessly. I also installed the Sennheiser app for further customization. Their ANC is not like that of the Sony MX5 headphones, but personally, I am satisfied. Sennheiser does sacrifice a bit of ANC, but it delivers on sound and then some (note: I have no experience with high-end Bluetooth headphones). Their price is a bit steep, but compared to other good high-end headphones, they are by far the best and the cheapest. If anything comes up, I will return for a reevaluation of the product.
21/08/24
The on-head detection feature sometimes does not work correctly, resulting in the music not stopping when you take off the headphones while music is playing, or when you put the headphones on, the music does not start automatically. However, there is the option to disable the feature I mentioned earlier. So you won't encounter the problems I mentioned. So all good

See on iFixit: https://www.ifixit.com/Answers/View/855159/Why+do+I+have+static+noise+in+my+left+earcup

ADDITION: After 2 years and 3 months: it died, it won't turn on, nor can it be reset. I had just changed the earpads which were not available in Greece, and I had to order them from Bulgaria at a price of 29.63 euros + shipping. I do not intend to take it for repair; Sennheiser products are finished for me.

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They must be the worst headphones ever made by Sennheiser, and this is because a setting is missing from the Software: the ability to turn off the ANC. The ANC does not work properly due to a bug and there is no option to turn it off. When there is a faint noise that should normally be ignored, since the headphones isolate you from that level of noise, a random annoying noise starts in one of the two headphones (also randomly, more often from the left). No matter what setting you make, you can't avoid it, and you start regretting the money you spent and hoping that at some point they might add an option to turn off the ANC.

Otherwise, they have the best sound I've ever heard and are really very comfortable for continuous use. Problems that existed when they first came out have been fixed (very bad pairing and that you could only connect to one device). Remaining problems are: it cannot turn off after a certain period of inactivity, only after a certain amount of time in general (i.e., after about 15 minutes where suddenly while you are listening to music they turn off), fortunately, it can be disabled. It detects when you put them on and take them off and can pause or continue the music, only that sometimes when you are talking in a meeting it suddenly mutes because you turned your head a little, it also turns off. The battery life is quite good, but much cheaper Sennheiser headphones (e.g., HD 4.50 BTNC) have a longer battery life without the unacceptable problems.

Conclusion: it is a product to avoid, prefer some other model.

The battery is the best among all other headphones in this budget. The wireless connection works without any problems. They can be used with a wired jack and usbc. They have nice features and a good app for the mobile phone. Be careful, something I didn't know before I bought them. In order to listen to the best codec supported by the headphones for wireless use, I mean, only with devices that support aptx-aptx adaptive. Apple has its own codecs and unfortunately they are only supported if you have airpods or beats. Windows only have the basic aptx from the 90s. With a cable, of course, depending on the sound card you have. In speech, however, wherever you are, the other person only hears your crystal clear voice. The ANC does not isolate 100% of external sounds, some pass through but it doesn't bother me at all, it's minimal. Something that bothers me is that my ears get warm after some time. I got the blue ones because they came out much later and I believe if there were any flaws in the previous ones, they would have fixed them in these.

Let me point out that I did not buy them new because the price was prohibitive. So, I bought them used. At first, there was a very strong parasite sound coming from the left earphone, which then decreased and now has disappeared (or sometimes sounds like vinyl scratching). I remind you: used. I paid 130€.

Once they recovered, I saw the light! 60 hours of battery life (actually 57-58, but close enough). Sound quality? EXCELLENT! The ultimate dream, with adjustable EQ tuning through the related application, to perfectly suit your preferences. Seriously, I'm not exaggerating, the sound quality is unprecedented for the average consumer, with warm, rich, and clean bass, while the mid-range and treble are exactly where they should be to provide the music with the detail and liveliness we desire. The sound is as sophisticated as it is accessible to the "uninitiated" (they don't exist, anyone with hearing is enough, but anyway, some people want a certain level of quality).

The Bluetooth connectivity with two devices simultaneously either confused me or the headphones, and I'm experimenting. However, for simple music and calls on a mobile phone, you will have minimal issues, and those can be solved with a restart on the phone and the headphones will work fine for several days. Not a big deal...

Apart from music, we can isolate external sound through ANC, which is not the best on the market (Sony claims that achievement), but it is still quite decent, especially for low frequencies. There is also the opposite, where one can hear their surroundings (through the microphone) - useful in my neighborhood, which lacks sidewalks. One can adjust how much they want to block or accept the outside world, and both extremes are available in the continuous application. As for those around you, you can listen to the music dangerously loud, and they won't even notice it's playing!

The microphones are very good for calls, although for some reason, my voice cuts off occasionally and I have to call again - not a big deal... One particularly good feature is that the microphone transfers the speaker's voice to their ear, so they don't have to shout by mistake - I find that lifesaving.

It fully charges in 2-3 hours. With a 15-minute charge when it's empty, you get 5-6 hours of autonomy if you're in a hurry. Total hours (with all the good features active) are 57-58 hours, as mentioned before.

Bluetooth is excellent: 17-18 meters with two doors and the load-bearing wall in between, on the stairs (and going downstairs to the floor level, Bluetooth doesn't cut off.

Bluetooth decoders range from basic to AAC/aptX Adaptive, allowing for CD-like quality (16-bit/44.1kHz). Your music will be crystal clear.

The construction is sturdy and quite high-quality, although it's made of plastic, it seems durable (mine were already used, but everything looks good).

They put a little pressure on my head, especially with glasses, but let's emphasize that people often mistake me for an African or Asian - definitely not Greek, so I have a big head... My ears don't get tired with all that, despite the glasses. I just feel a slight squeeze because of my head. I have to take them off after 3-4 hours for about a quarter, and then everything is fine. The headband can easily withstand the pressure, and the weight distribution is excellent. They won't fall off your head. Only to a certain extent...

Finally, the right earphone is touch-sensitive, and you have full control over everything with simple gestures. The application contains detailed instructions (and there are probably various pages on the internet). Lifting the right earphone, the music stops until you put it back in its place (it functions correctly). If you take them off and leave them for about 15 minutes, they automatically turn off and come back to life when you pick them up to wear them, saving battery (which already lasts twice as long as comparable Sony products).

All functions can be modified in the application, according to your preferences.

If your budget allows it, get them. I overcame my selfishness, cleaned them with a little alcohol, and I have no regrets!

For at least 1 year I was trying to decide between the momentum 4 and the sony wh1000mx5 until I realized 5 things in the audio field, finally Sennheiser knows what it's doing. It lacks a bit in anc compared to the mx5 but performs much better in sound, it's impressive how Sennheiser has managed to produce something in this category that is not neutral but remains crystal clear with very good imaging and commendable soundstage for close back headphones.
Additionally, we are talking about very versatile headphones where depending on how and where you connect them, they perform differently, bluetooth with aptx adaptive or aptx hd plus the bt600 dongle gives you aptx adaptive with superior performance on pc.
Then you can simply connect it via usb using the internal DAC for lossless while maintaining all functions such as anc.
And the 2.5mm aux is not missing, if you have an amplifier/dac better than the internal one, you can unleash what the drivers have to offer!
In terms of price, it's the best, period.
For something better, you're looking at 600 euros and above with the differences not justifying the cost, it's better to go wired.
As for the ANC, it's very close to Sony's, I work in a noisy environment and even with high-frequency noises, with the music volume at 50-60%, you don't hear anything, while without music, it's like listening from inside a closed room, in general, it even covers isolation in demanding conditions so you can focus on your work.
The transparency is unbelievable! It's almost like not wearing headphones.
In terms of comfort, I wear them for 8 to 10 hours a day without feeling tired at all.
The battery with 60% volume indeed lasts at least 60 hours.

I was torn between these and the Sony WH1000 XM5. I had the opportunity to try out the Sony ones before purchasing, and I hesitantly chose the Momentum because I didn't have the chance to listen to them, but I have confidence in Sennheiser as a brand and I know and like their sound signature. And of course, I read whatever reviews I could find on the web.

Luckily, I didn't regret it at all.
The sound quality is exceptional. Incredible detail with clear sound. Out of the box, there is a particular emphasis on the low frequencies, but this can easily be adjusted with the EQ in the app if someone wants a more balanced sound.
Otherwise, they are flawless. Very comfortable and don't tire out even after hours of use, the battery life is the best on the market, and the gestures on the earcup have good responsiveness and are user-friendly.
The ANC is decent, but the Sony ones are noticeably better. The Momentum mainly blocks out low frequencies/background noise, so I assume they would be great for use on an airplane, but they fall behind in urban environments.
The connectivity is very good, and switching between multiple devices is okay.
They also have an auto on/off feature that (usually) works correctly and is convenient, although sometimes it does its own thing. But that's a minor issue.

In conclusion, personally, the most important feature of a pair of headphones by far is sound quality, and in this aspect, they are ahead of the competition in their price range, and therefore they provide a (relative) value for money. So, I highly recommend them.