Sennheiser CX400BT Review: Subtle everyday buds

Quick verdict: The brand has some serious audio credentials, but the Sennheiser CX400BT are more everyday models in the mid-range. That’s no bad thing, however, as these are very good headphones if you don’t favour the stalk microphone approach of so many true wireless buds.


  • Clean sound
  • Simple design
  • Comfortable
  • Touch controls work well

  • Only passive noise cancelling
  • Middling battery life
  • Treble bias doesn’t suit every music style

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Sennheiser as a brand sells itself on pure audio quality, and much of what you can get from the company in consumer headphones tends towards the higher end of the market. That's not the story that the Sennheiser CX400BT headphones want to tell, however.

The Sennheiser CX400BT are a set of more moderately priced headphones designed and pitched for folks who might think about sets like the standard AirPods and their many, many competitors, but for whom either the Sennheiser name has allure, or the simplified design fits their style just that little bit better.



  • White or black colour choice
  • Compact case
Sennheiser CX400BT

There's certainly not that much to say about the Sennheiser CX400BT in terms of design style. Each bud is either a small black or white primary enclosure with a tip sticking out of each side. The idea here is audio by stealth; while my own lack of hair makes it immediately obvious that I'm wearing them, anyone with even mid-length hair should be able to obscure them completely while wearing.

Like so many true wireless buds, you get a choice of rubber tips in the box to pick from, although I found the default mid size fit quite nicely into my own ears. They're designed so that you pop them into your ears and give them a very subtle twist to lock them into place, which works quite well.

Just like the buds, the Sennheiser CX400BT's case is also pretty unremarkable, although it does at least avoid the trap of being overly large or oddly shaped such that it might roll or slip away from you. It somewhat resembles a small ring box with the Sennheiser S logo on the top and USB C charging port at the rear.



  • Clear audio with little bass
  • Good app-based EQ controls
  • Touch controls are surprisingly good
  • Firmware updates are exceptionally slow
Sennheiser CX400BT

Like many of its competitors, Sennheiser keeps it pretty simple when you're setting up the Sennheiser CX400BT headphones for the first time. They're immediately available for standard Bluetooth pairing out of the box, or alternatively via the Sennheiser Smart Control app, which you'll want to install at some point unless you're entirely happy with the default equalisation.

If you do need to pair to a new device, they use the same approach as many of Sony's true wireless headphones, requiring you to touch both headphones' touch-sensitive areas for an extended period of time while in your ears. I'm not a big fan of that approach, partly because you look very weird while doing it, but also because it can be very imprecise if you're just trying to connect up a new audio source in a hurry.

The price point of the Sennheiser CX400BT means that you don't get fancy active noise cancellation as you do on more premium-priced sets, but the passive isolation is actually pretty decent once they're in place.

That's also how I'd describe the default sound on the Sennheiser CX400BT, which is why you're probably going to want to play around with the equalisation in the Sennheiser app. The default neutral setting tends to accentuate treble over bass, which won't suit everyone's audio style.

As an example, for the Foo Fighters "Making A Fire", the drum kick of the cymbals comes through very clearly, but the lower guitar and vocal tones do lose just a little oomph to my ears. Tweaking towards the bass ever so slightly improved this a lot, but you've got to be quite careful not to lose detail by punching it too hard.

Sennheiser gives you a visual and slider-based EQ approach with the ability to save custom presets within the app. Whichever you choose is transferred to the headphones and saved there until you tweak it again, so you don't need the app running to get your preferred audio setting. One issue here is that Sennheiser doesn't provide any settings beyond the default neutral if you wanted a guided approach, so you've got to feel it out for yourself.

With that slight bass tweak, I set about testing the Sennheiser CX400BT's audio chops. That slight bias towards treble does suit some tracks quite well – Taylor Swift's "No Body, No Crime" gains a lot from a more subtle, balanced approach – but naturally others might not sound quite as good to your ears. Throw NWA's "100 Miles and Runnin'" at them, and with that default neutral profile there's a distinct lack of impact.

The Sennheiser CX400BT uses touch controls, with the left bud controlling playback while the right handles assistant duties for either Siri or Google Assistant. I'm typically not a big fan of touch-based controls because they can be so imprecise, but I found myself actually rather liking the Sennheiser CX400BT's approach, as long as I kept it simple. Basic play/pause and Siri/Google invoking works well, although predictably using multi-taps for track skipping is rather less precise.

The Sennheiser Smart Control app is also how the Sennheiser CX400BT handles firmware updates. It's great that Sennheiser is tweaking its software and ironing out the bugs, but the one catch here is that it can be slow.

Not just slightly slow, but exceptionally slow, and it does warn you of this. For the firmware that came down the line during the review period, the app warned me that updating might take around 40 minutes, or slower if I wanted to keep streaming music while doing so. It wasn't kidding either, with a glacially slow update process even on a quick broadband connection.

Battery life

Battery life

  • 7 hours battery life out of the case
  • 20 hours in total is good, but not great
Sennheiser CX400BT

The Sennheiser CX400BT headphones advertise around 7 hours of playback out of the box, with just under another two recharges available from the case for a total of 20 hours. That's a reasonable figure for a set of true wireless buds, but it's not right up there with the very best in the market.

Your own experience will depend on how heavily you tax the volume and Bluetooth connectivity of the Sennheiser CX400BT. In my own tests I averaged around 5-6 hours with moderate volume, but I was also stretching out the Bluetooth distance and rather deliberately torture testing the headphones. That 7 hour figure certainly feels approachable.

Should you buy the Sennheiser CX400BT?

  • Buy it if you want a subtle and simple set of true wireless buds.
  • Don't buy it if you want a more solid set of headphones or more bass.
Finder score: 3.5
How we score our reviews

The Sennheiser CX400BT do offer good audio and an overall pleasing sonic experience for most music types, and their comfortable fit is also a big plus. They're not the most solid feeling set of headphones, however, and their battery life is only average for a set of headphones in this price bracket.

Pricing and availability


The Sennheiser CX400BT retail in Australia for $299.

Where to buy


Sennheiser CX400BT
Finder score: 3.5


Frequency Response
5 - 21,000 Hz


Bluetooth Version
Bluetooth Profiles


Noise Cancelling
Rechargeable Battery
Battery Life
Up to 7 hours
Battery Charging Time
1.5 hours
Battery Type
Built-in Lithium-Ion rechargeable batteries

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