Sennheiser CX 400BT review

These true wireless earbuds are excellent value for money Tested at £99 / $100 / AU$149

Sennheiser CX 400BT review
(Image: © Sennheiser)

What Hi-Fi? Verdict

While slightly compromised in the features department, the CX 400BT are sonic marvels – and, at this price, hugely appealing


  • +

    Lively, detailed sound

  • +

    Lightweight fit

  • +

    Excellent value for money


  • -

    Battery life below the best

  • -

    Not waterproof

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Such is the popularity of true wireless earbuds today that you can go to the website of many established headphone brands and take your pick from several models across a range of price points. Sony, Bose and JBL, for example, all have at least a few pairs in their line-up.

But Sennheiser’s offering has, like Apple’s, been streamlined down to two models: the premium, noise-cancelling Momentum True Wireless 2 and the more affordable CX 400BT without noise-cancelling that we have on test here.

Sennheiser would no doubt argue the case for quality over quantity, and while the CX 400BT may not have the sleekest name, the fanciest design or even the most generous feature set, they are more sonically gifted than most at this level.

These Sennheisers launched at double the price but now inhabit the increasingly populated £100 ($100, AU$150) arena, making them some of the best-value budget earbuds we’ve come across.


Sennheiser CX 400BT build

(Image credit: Sennheiser)

Compared with the excellent Momentum True Wireless 2, the CX 400BT lack active noise-cancelling, smart pause functionality and IPX4 splash resistance, and have an inferior battery life. Their specs next to their pricier sibling seems fair and is to be expected, although we would like to see a few more features from the CX 400BT.

Sennheiser CX 400BT tech specs

Sennheiser CX 400BT

(Image credit: Sennheiser)

Bluetooth version 5.1, aptX

Battery life 20 hours

Charging USB-C

Weight 6g (each earbud)

Their combined battery life is 20 hours (seven hours from the buds, plus a further 13 hours from the charging case), which is less than that offered by the Cambridge Audio Melomania Touch (50 hours) and Melomania 1 (45 hours), the Earfun Air Pro (35 hours), JBL Reflect Flow (30 hours) and Apple AirPods (24 hours).

We’d also like some degree of sweat- or water-resistance, as featured on many of the Sennheiser’s rivals. Without that, the CX 400BT aren’t recommended for sportswear, and you don’t get the peace of mind that they’d survive being caught in a rain shower.

They do support Bluetooth 5.1 support and mobile app features, though – neither of which is a given at this level. The former promises high-quality, far-reaching Bluetooth transmission, while the latter opens doors to EQ adjustment and control customisation.

Out of the box, the left earbud can be tapped once to play or pause music, twice to jump backwards a track, and held down to reduce volume. On the right earbud, one tap activates your phone’s voice assistant or accepts incoming calls, two taps jump forward a track or rejects calls, and holding it down increases volume.

The playback functions can be reallocated or turned off in the Sennheiser Smart Control app, which is also where you can alter the earbuds’ EQ and save EQ presets. However, unless you’re someone who often adjusts the EQ, it’s likely you’ll use the dedicated app once during set-up and then rarely, if ever, again. 


Sennheiser CX 400BT comfort

(Image credit: Sennheiser)

While touch controls can sometimes be hit and miss with earbuds, the relatively large, flat surface area of the CX 400BT’s touch panels make the controls easy and reliable to use. The Sennheiser’s design is more functional than fancy, but that’s more of an observation than a complaint. And besides, who can argue with designs that just work?

Their oval housings require a push and twist motion for them to nestle nicely in the ears – we’re talking a bit of encouragement, rather than any forceful manhandling – and when in place are comfortably lightweight (6g each) and unobtrusive.

They are just over 2cm deep, so will protrude slightly out of shallower ears. The fit is as versatile as you’d expect, thanks to the four different sizes of silicone ear tips included in the box.


Sennheiser CX 400BT sound

(Image credit: Sennheiser)

Sennheiser is one of the most consistent brands when it comes to sound quality, so expectations are high as we play The Weather Station’s Parking Lot via Tidal. The CX 400BT are instantly likeable: they’re lively and clear-cut, and their relatively open presentation is infused with clarity and generously peppered with detail.

Their inherently energetic, musical nature, which is forward yet not exhausting, can’t help but lap up the track’s jaunty piano melody and bassline. As cymbals, strings and vocals come into the increasingly dense mix, the Sennheisers manage to keep a tab on everything in the name of rhythmic precision.

Similarly, play Black Country, New Road’s Instrumental from their debut album and the rhythm track is presented with gusto and insight. If anything, their up-for-it presentation makes it all the more frustrating that the CX 400BT aren't particularly good running headphones, because they would undoubtedly spur you on to reach that finish line.

There is enough in their sonic repertoire to keep them interesting when their zest isn’t required, too. Bass is taut and agile, mids are expressive and particularly open, and a crisp, present treble doesn’t let the side down. There’s plenty of detail and dynamic subtlety in a more technical, classical track, such as Ólafur Arnald’s piano-led nyepi, although if your budget can stretch to the likes of the pricier Sennheisers or Sony WF-1000XM3, there is a clear step up in class when it comes to outright transparency.

It has to be said that the CX 400BT’s sparkle comes at the expense of a little refinement. The similarly priced, five-star Panasonic RZ-S500W, for example, offer a smoother, more sophisticated balance that has a level of finesse we wish the Sennheisers possessed – even if the CX 400BT counter with a more energetic listen.


When you have two superb-sounding true wireless earbuds in your arsenal – one with ANC at the premium end of the market, and one without at the more affordable end – why would you need any more?

We would have liked the CX 400BT to have a more versatile, sportier design, and perhaps this is where a third pair of truly wireless Sennheisers could be justified, but there’s no doubt that the reputable German audio brand has mastered the sound quality aspect. The CX 400BT would have been recommendable at their original launch price, but now discounted, they are truly excellent value.


  • Sound 5
  • Comfort 5
  • Build 4


Read our guide to the best wireless earbuds

Read our Panasonic RZ-S500W review

Read our Sennheiser Momentum True Wireless 2 review

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