Trusted Reviews is supported by its audience. If you purchase through links on our site, we may earn a commission. Learn more.


Some may lament the lack of ANC, but the CX 400T deliver where it counts: sound. With a similar audio performance to the premium Momentum TW2, they offer excellent audio at a more affordable price.


  • Excellent sound
  • Pretty comfortable to wear
  • Unassuming design


  • Volume limited
  • Battery life slightly disappoints

Key Features

  • SBC, AAC, aptXSupport aptX for higher-quality Bluetooth playback
  • Sennheiser Smart Control app App is available on Android and iOS platform and offers various customisation


The Sennheiser CX 400BT are the latest earbuds from the venerable German audio brand, sitting beneath the award-winning MOMENTUM TW2.

2020 has seen the popularity of wireless earbuds grow further, becoming the option for those who want portable audio on the go. The past few years have seen a focus on the premium and budget ends of the market, leaving a space right in the middle. Apart from a few notable efforts – such as Audio-Technica’s ATH-CKS5TW – and some decent headphones from the likes of Google and Samsung, no one has taken the bull by the horns.

Sennheiser hopes to change that with the CX 400T, which aim to offer premium sound at a more affordable price and make their mark in that Goldilocks area where performance and affordability meet.

The Sennheiser CX 400BT were announced just ahead of IFA 2020 for £169 / $199 / €199. As of March 2021, you could find them as low as £99.


  • Rather anonymous looks
  • Compact build
  • Comfortable fit

The Sennheiser CX 400BT pack a slightly different design to the MOMENTUM True Wireless 2, making it fairly clear they are not part of the MOMENTUM range, at least not in aesthetic terms.

Surprisingly though, the CX 400BT are the more compact of the two. Fractionally slimmer in terms of build, the touch panels are square in shape instead of oval. There’s the distinctive Sennheiser logo on the touch panels but the colours are reversed (silver and black). Like the TW2 they come in white and black finishes.

Black Sennheiser CX 400T earbuds resting in it's black case standing on a table

I’ve not had any problems in terms of comfort, with the CX 400BT slotting in the ear easily with a twist to lock fit. There’s also been no sign of any fatigue or the kind of oily sensation that some true wireless can cause over extended periods. The fit is tight and suppresses external sounds well, but there’s enough leakage to hear what’s around you in case you need to react to something. Sennheiser has supplied ear tips in four sizes (L, M, S, XS) should the default option not fit.

I mentioned in the Momentum TW2 review that they weren’t the most desirable or flashy earbuds and that’s true of the CX 400BT. There’s something unassuming about them – more function over form. They’re not concerned with lighting the headphone market up with their style. so say the least.


  • Only 20 hours of battery life
  • Supports quick charging
  • Supported in Sennheiser Smart Control companion app

There’s no active noise cancellation, transparent mode or smart pause functionality, and that’s not unexpected for the £169 asking price. Few others have smuggled in ANC at this price (though that’s beginning to change) and I imagine Sennheiser wouldn’t want to undercut its own 2nd gen MOMENTUM earbuds either.

Black Sennheiser CX 400T earbud's case standing on a table

Battery life delivers 6.5 hours, with the charging case providing another two charges for twenty hours in total. It’s a respectable amount, but with the likes of the ATH-CK5TW offering 45 hours – and for less money – you’d have liked the Sennheiser pair to go a bit longer.

The charging case is also pretty compact – in fact it’s dwarfed by the TW2’s case. It can be flung into a pocket no problem, and like the earbuds it’s fairly unassuming in terms of how it looks. Charging is through a USB-C cable with quick charge delivering one hour of playback from a 10 minute charge and 90 minutes required for a complete top up.

Bluetooth 5.1 is the wireless connection and despite the premium sound claims there’s no support for LDAC or aptX-HD. There is SBC, AAC and aptX for wringing a tune out of whatever mobile device the Sennheiser CX 400T connects to.

Screenshots from Sennheiser CX 400T earbud's application abour earbuds control, device settings and equalizer

The headphones support Alexa, Google Assistant and Siri (though none are built in) and they’re compatible with the Sennheiser Smart Control app (Android, iOS). Here you can customise audio via the equaliser, alter the controls and update the firmware. The app is slick enough to use and fine for what it does, though you can never quite budge the feeling that it could be stocked with more features.

And more about that control scheme. The default option is that the left earbud controls playback (one tap), skips back (two taps) and nudges volume down (hold). The right earbud sees a tap activate the voice assistant of choice, two taps skip to the next track and a long press for volume up. It’s relatively easy to keep track of, and shouldn’t cause any confusion when using them. No function is assigned to tapping thrice on either side, with the only option to map the previously mentioned features there.

Sound quality

  • Same 7mm drivers as premium Momentum TW2
  • Transparent and revealing sound
  • Confident bass handling

The CX 400BT have the same 7mm drivers that feature in the MOMENTUM TW2 (which we bestowed our best true wireless award 2020). Sennheiser says its gone down this route because its bespoke acoustic system delivers high-fidelity stereo sound, deep bass, natural mids and clear treble. Considering the TW2’s performance, we can’t disagree with that statement.

And the difference between the MOMENTUM TW2 and CX 400T’s performance isn’t as big as the difference in price. I half-expected that they’d be a drop in performance, but that isn’t the case at all. The CX 400BT have the attributes and characteristics that made the premium option such winning performers. At the very least they’re an accomplished sounding pair.

View from top of black Sennheiser CX 400T earbuds resting in it's black case

The sound they offer is transparent and revealing, one that doesn’t allow itself to get carried away or become over exuberant. Whatever track or genre that’s put through the CX 400BT, they exhibit a level of control over it in terms of detail, clarity and dynamism that trumps its closest midrange rivals.

Vocals – male and female – are handled with precision and clarity and brought a little further forward in the mix than they are on the TW2. There isn’t quite the same level detail or warmth as on the MOMENTUM TW2 – more neutral and dry, so to speak – but they’re nevertheless a consistently engaging listen.

The size of the soundstage they produce is big and expansive, rarely feeling over encumbered or too cluttered. Mid-range performance is key, extracting plenty of detail and displaying an expert sense of timing. Everything feels unified and coherent in Regina Spektor’s cover of While My Guitar Gently Weeps, but more than that is how natural they come across.

Sennheiser CX 400BTBlack Sennheiser CX 400T earbuds resting on ground

Dynamically there’s no doubting the difference between low and high, and rhythmically they display a toe-tapping enthusiasm in David Bowie’s Young Americans, confidently flowing from one beat to the next in tightly knitted presentation.

Bass is handled just as confidently, adding a bit of beefiness to the low end where necessary without becoming tubby or flabby. Treble frequencies are capably handled for the most part, and while the CX 400BT resists become strident in its reproduction, the very top end seems to become just a little unfocused when given a fairly piercing track to deal with, such as Jonny Greenwood’s Boletus Felleus from The Phantom Thread soundtrack.

One minor qualm is that the CX 400BT do seem volume limited compared to the TW2. It makes them sound a little more restrained and less exciting in some moments.

Should you buy it?

You want really good sound without breaking open the piggy bank: The Sennheisers are one of the best we’ve heard at their price. They sound super without costing too much either.

If you want ANC: Some may lament the omission of active noise cancellation, but I don’t think that’s a big loss here.

Final Thoughts

Some may lament the lack of ANC, but the CX 400T deliver where it counts: sound. With a similar audio performance to the premium Momentum TW2, they offer excellent audio at a more affordable price.

Trusted Score
rating-star rating-star rating-star rating-star rating-star

Sign up for the Trusted Reviews Newsletter

How we test


Why trust our journalism?

Founded in 2003, Trusted Reviews exists to give our readers thorough, unbiased and independent advice on what to buy.

Today, we have millions of users a month from around the world, and assess more than 1,000 products a year.

author icon

Editorial independence

Editorial independence means being able to give an unbiased verdict about a product or company, with the avoidance of conflicts of interest. To ensure this is possible, every member of the editorial staff follows a clear code of conduct.

author icon

Professional conduct

We also expect our journalists to follow clear ethical standards in their work. Our staff members must strive for honesty and accuracy in everything they do. We follow the IPSO Editors’ code of practice to underpin these standards.