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Hands-on review: Sennheiser CX 400BT earbuds
Mon, 2nd Nov 2020
FYI, this story is more than a year old

A month or so ago, I accidentally sat on my beloved over-ear headphones, and the result was a perpetual crackling noise emanating from the left ear cup. Luckily for me, the headphones were still under warranty — unluckily for me, this meant I would be headphone-less for over a week while they were being repaired.

But then luck struck again, because Sennheiser emerged in the nick of time and sent me their latest CX 400BT True Wireless in-ear earphones, and the horrifying notion of walking 30 minutes to and from work every day without listening to my podcasts was averted.

These were the first earbuds I had ever tried (I prefer over-ear headphones), but after a couple of weeks using them, I was pleasantly surprised at how much I liked them. So how did they hold up generally?

Design and comfort

The CX 400BT earbuds come in a sleek, compact black box, easily slippable into a standard pocket. You can simply drop the earbuds into their slot, and the magnetic pins clip themselves into place with ease.

Design-wise, I think I would have preferred that the actual earbuds were circular, as opposed to square. This would have meant I could have averted the confusion over what was the correct way to insert them into my ears; I found I needed to rotate them 90 degrees upon first inserting them a few times to get them just right.

Once they were in, however, I liked how they looked: not too big, not too small, and unmistakably Sennheiser.

My usual aversion to earbuds is solely based on my general unwillingness to put things inside my ears, but as comfort goes, these were as good as I could have expected. They fitted nicely, and come with different sizes of attachable rubber pieces to cater for different ears. I forgot that things were in my ears after a while, which is a definite plus.

Controls, Bluetooth pairing and app

One of the best things about the CX 400BT is its customisability. I sometimes get frustrated at headphones when the touch controls aren't as intuitive as I want them to be — with these earbuds, I can fine-tune them within an inch of their lives.

For example, in the Sennheiser Smart Control app, I can change the pause control from being a tap on the right earbud to being a tap of the left earbud. Users can customise phone call controls, Bluetooth pairing, song skipping and more using this method.

The app also allows you to see a list of all paired devices and provides the option to rename the earbuds. The EQ customisation tool is also highly customisable, letting users get a listening experience that is just right.

One of the most significant problems I found, however, was the Bluetooth pairing. Pairing to one device is fine - but trying to pair to a second device is where it gets a little tricky.

The earbuds can't pair to two devices at once, so if I wanted pair to my laptop after listening to music on my phone, I would need to turn off Bluetooth on my phone and set the earbuds on ‘bluetooth seeking mode' to connect to the laptop — even if it had been connected to it before.

Sound and battery life

The highly customisable EQ combined with Sennheiser's stellar reputation for good quality sound engineering come together to make for a great sounding pair of earbuds.

My listening lifestyle consists more of podcasts and videos (Netflix, YouTube, etc.) than music, and I like to have good quality bass when I watch TV series or movies. Once configured in the EQ customiser on the app, the CX 400BTs work really well — better than I expected for a small pair of earbuds.

While it doesn't achieve the depth of sound you get by wearing an over-ear pair of headphones, I was pleasantly surprised at how much I could get out of these earbuds. While these particular earbuds don't feature active noise cancelling (ANC), they still did a reasonably decent job of keeping noise out, and I found I could work at my desk without distractions almost as well as my ANC-equipped headphones.

There was minimal noise leakage too, which is always a bonus — someone standing two or three feet away from me reported hearing nothing when I had the volume turned up to three-quarters capacity.

Lastly, the battery life seemed consistent with its advertised length of 20 hours, which is already an excellent number for a pair of earbuds. I found I could go two or three days on one charge, which I was definitely impressed with.


At NZ$330, these earbuds are at the top-end of the market — and for the most part, they live up to the price point.

The app is well-designed, highly customisable and intuitive, battery life and sound quality are both excellent, and comfort-wise they are as good as someone who dislikes putting things in their ears can expect.

The only real pitfall is the Bluetooth pairing, but for those with one or two devices they would use with the CX 400BTs, these should definitely be near the top of their Christmas list.