Sennheiser CX400BT True Wireless Earbuds Review

Posted on 6th November, 2020

Sennheiser CX400BT True Wireless Earbuds Review

Sennheiser has slimmed down its flagship IEM. It has cut the price – but what of the quality, asks Matthew Jens?



True Wireless Earbuds

AUD $299 RRP

I have come to accept my place in life as “the headphone guy”. Within my own family and friends, I'm the weird headphone enthusiast that everyone goes to for help when they want to make a new purchase. It's okay, I have accepted this fate, and part of me enjoys it. When it comes to true wireless IEMs, there are a few “staple” recommendations that I have for various price points. For flagships, the Apple AirPods Pro and Sennheiser Momentum True Wireless 2 are easy to praise. Yet I'm often lost for words when there's a request for a more budget-friendly offering – someone who is happy to shell out a few hundred for something decent, but not wanting to go “all-out”.

Sennheiser, for the past few years it seems, was struggling to find the right words too. While other brands have been scrambling to find their David to fight the massive AirPods Pro Goliath, this company has been releasing superb products that aim to appeal to the more refined, sophisticated audio palate. With the sophisticated yet budget-conscious customer in mind, it has created the CX400 – a middle-tier true wireless IEM which takes some of the elements from the award-winning Momentum series and trims down the fat and price.

This is a bold strategy from Sennheiser. Not every manufacturer would take a brilliant flagship product and trim down the build, remove some of the fancy features and extras, whittle it down to a cheaper product, but retain the same drivers and sound signature. Will this new slimmed-down release make its way to my recommendations? Or did the company's design engineers get a bit too enthusiastic with the scissors and trim too much fat off?


The elephant in the room is that just months ago, Sennheiser released a flagship model into the market, which is just shy of being double the price of this new release. When I questioned a company spokesperson about which parts made the transition from the flagship to this new model, they said the similarities between the two models, “include 7mm dynamic drivers with a built-in equaliser, as well as an ergonomic design, customisable touch controls, calls and voice assistant access, as well as support for SBC, AAC and aptX Bluetooth codecs.”

Well, this all sounds great in theory – there's a considerable price drop, while retaining some of the best parts of the flagship. However, when questioned on what didn't quite make the cut, Sennheiser informed us that, “the Momentum True Wireless 2 adds enhanced features such as ANC and Transparent Hearing, smart pause, IPX4 splash resistance, typical Momentum craftsmanship and 28-hour battery life, compared to 20 hours for the CX 400BT True Wireless.”

So lo and behold, the 'smoking gun' is revealed! There is no water resistance, no smart pause features, no noise-cancelling or ambient noise features and less battery life. While Sennheiser claims that the CX400 doesn't have Momentum craftsmanship, I would struggle to say this model is poorly made. Sure, the plastic charging case isn't the most pretty thing in the world and is prone to scratching if you throw it in a bag next to some keys. Also, the weird decision to make the outside of the IEMs a rectangular shape is odd.

Yet these quirks thankfully don't apply to the fit and comfort. The outside of the units may be rectangular, but the inside is neatly contoured and sits against the inner ear with ease. Insertion is as quick as jamming them into the ear canal, and getting a good seal requires little more than a quick poke with a finger. The medium tips fit me just fine, and there are four different sizes to choose from if you don't have the same experience.

The usual Sennheiser software tweaks are available here, which is excellent because as far as I'm concerned, these are nearing best-in-class levels of greatness. A customisable EQ (saved to the earbuds, not the source device), customisable touch controls and voice assistant abilities are all here, and working flawlessly.

The lack of noise-cancelling ability is noticeable, but for the price point, no points are deducted for this. In all honesty, not having several noise-cancelling and transparent hearing features made life a lot simpler; it's one less thing to think about. Just pop these in your ears for a consistent experience each time. When I was using these on my bike, I didn't get any intrusive wind noise due to them being on the wrong setting – they just worked. It's the simplicity that makes the CX400 shine. Sure, the battery life is reduced compared to its older siblings, but 20 hours is still nothing to sniff at; these kinds of numbers are only a stone's throw away from the AirPods Pro.


One of the core differences between the Sennheiser True Wireless Momentum and True Wireless Momentum 2 was the new 7mm driver. Upon seeing a new true wireless release, I immediately shot the question to Sennheiser, asking if this was a new driver once again. The answer – surprisingly – was that the CX400 uses the same drivers and internal acoustic system as the Momentum True Wireless 2. “Well then,” I thought. If that's the case, let's see how the two compare… 

I decided to try this out by throwing the highly eclectic Bias by Floating Points at the CX400. Upon doing so, I was delighted to find a familiar, ever-so-slightly lively, upper midrange and the same rambunctious low-end response as the Momentum TW 2. To me, this is a tribute to the glowing bass of the Sennheiser greats such as the HD-25ii. The raw emotion of this track, as well as its tiny, odd, weird, offbeat details, are retained nicely within this design. The quieter moments might let in a bit more outside noise than most IEMs do, as the plastic build of this product is fairly forgiving to external noise.

I then decided to throw something decidedly more analogue at the CX400 to see how it would fare. The song choice: Black Sands by Bonobo. Upon hitting “play”, the gentle plucking throughout the whole song was immediately brought to life, rendering every note with a soft, detailed air that was never overpowering, bitey or peaking. As the instruments jumped into the mix, each was easily identifiable without getting too congested or muddy along the way. There was plenty of separation between instruments, and a soundstage of adequate width for this format and price point. 

The dynamic range is also impressive here, albeit slightly affected by the isolation being a little lower than I'm used to. Still, in the right environments, songs like Say Something by Flying Lotus retain every single string instrument pluck, with plenty of nuance and body. This new Sennheiser release is excellent for “out and about” usage as wind noise isn't a problem. It won't completely isolate you from traffic noise if you're crossing the road, either. 

Gone are the volume headroom problems from older Sennheiser releases, too. I can't bring the CX400 to full volume even for a few seconds; it's just too loud. Dangerously loud. While I can't recommend you do this to your ears, the Sennheiser will allow loud, crisp, clear and punchy response with higher volumes if that's your thing, without any distortion or struggling at all.

On occasion, there is a faint hissing in the background when the units are switched on with nothing playing. It wasn't as bad as the original Momentum True Wireless 2 at release and before the software update that fixed the issue, and it's something I would consider to be forgivable.

What isn't forgivable sadly, is the latency experienced with video content. When music is playing, it's not an issue, but watching videos or TV shows is admittedly tricky when the audible component of the content is behind what's happening on screen. The problem was worse with Android devices; Apple devices (using the appropriate codec) seemed much snappier. While I understand this is partially a problem with Bluetooth overall, I have seen other Sennheiser products handle this issue with more grace. I've said it before, but I'll repeat it: Sennheiser, please bring back the aptX-LL (Low Latency) codec! 


The CX400 is a well-rounded release, with no bells and whistles, that gets plenty of the fundamentals right. What we are witnessing here is a bold strategy from Sennheiser – take a brilliant flagship product, trim down the build, remove some of the fancy features and extras, whittle it down to a cheaper product, but retain the same drivers and sound signature.

I'm thankful that Sennheiser has done this. After all, I'm the “headphone guy” within my friends and family, and so when someone now asks me for a recommendation in the midrange price point, I know exactly which direction to point them in. This one is an easy recommendation to make. 

For more information visit Sennheiser

    Matthew Jens's avatar

    Matthew Jens

    Constantly keeping himself busy, Matthew is a production manager, Brazilian jiu-jitsu blue belt, Head-Fi fanatic, coffee enthusiast and all-round cool Dad.

    Posted in:Headphones Applause Awards 2020 Headphones In Ear Monitors Noise Cancelling
    Tags: sennheiser 

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