Consumer Electronics, Gadgets & Accessories

CX 400BT: Sennheiser wants to play in the midfield (for once)

The German manufacturer of audio technology Sennheiser is known for exceptional sound quality and hefty prices. The latter are justified in most cases. To what extent price and performance are coherent in the CX 400BT wireless in-ears, we will get to the point in this review.

The CX 400BT are not meant to be a “cheap” copy of the MOMENTUM earphones, which are the flagships of the traditional company and are always at the top in terms of performance. Rather, Sennheiser has created a product that can meet the high expectations, but should play in the midfield in terms of price. It’s self-explanatory that some compromises had to be made.

We put the Sennheiser CX 400BT, the newest member of the wireless audio family, to the test to find out what the trade-offs are, and whether they are worth the money. Minor spoiler: We found that Sennheiser can never disappoint in terms of sound – even for 125 euros.

Technical data

Design In-ear with touch control
Driver 7 mm dynamic driver
Frequency response 5 – 21,000 Hz
Tone distortion at 1 kHz <0.08% (1 kHz = 94 dB)
Frequency response (microphone) 100 to 10,000 Hz
Battery life Up to 7 hours with music playback / Up to 20 hours music playback with charging box
Charge time 1.5 hours for full charge / 10 minutes for 1 hour
Connection Bluetooth 5.1
Audio codecs SBC, ACC, aptX
Connection USB-C
Compatibility iOS, Android
Dimension (box) 59 x 33.8 x 42.3 mm
Weight 49 g (total) / 6 g (one headphone)
Material Plastic / silicone (ear adapter)
Colors Black, White
Price € 249.99 *

What’s inside

The CX 400BT delivers Sennheiser in a narrow, inconspicuous packaging, which can be found with a different name on it numerous in electronics stores. But it’s the inside that counts in this test as well.

Unpacked, we find the in-ears in the designated case, which also serves as a charging station. In addition, the scope of delivery is supplemented by four ear adapters in sizes XS, S, M and L; which pretty much covers every ear type. The package also includes the USB charging cable and, of course, the obligatory manual.

In the end, it contains what is to be expected – nothing more, nothing less.

Purely pretty to look at on the outside

When it comes to the case of the earphones, Sennheiser has opted for a slightly more compact, almost chunky look than you might be used to from the MOMENTUM earphones. In general, however, they still look high-quality and classy, as you would expect from products from Sennheiser. Accordingly, even budget in-ears from the company look and feel even better than many others in the price range.

The earphones have a square but rounded design, and the Sennheiser logo is emblazoned on the outer surface. This also serves as a touch control, which we will get to later. The entire case is made of sturdy plastic.

On the inside, you can see the contact points for charging, as well as a small status LED. Otherwise, the earphones are kept absolutely simple in both colors – black and white. One does without material highlights or other accents.

The charging case also follows the same simple design. Only a strip around the edge of the opening is glossy. Otherwise, the color was kept matte here as well. What is particularly striking is the size of the case. With a length of just 59 millimeters, it fits in any jacket pocket. Only the minimum of material was really used here so that both earphones and a battery fit in. Of course, luxury packaging is not to be expected at this price.

Well-known sound by Sennheiser

The Sennheiser CX 400BT are equipped with a custom-made 7-millimeter driver, which brings a familiar good sound to the ears. Whereby good is also an understatement in the case of the CX 400BT. Although these in-ears have to do without Active Noise Cancellation (ANC), you still get to hear excellent sound without the in-ears focusing on one frequency range – also thanks to a distortion factor of less than 0.08 percent. Whether bass-heavy, midrange or clear high notes, the CX 400BT live up to their creator’s name and balance the sound perfectly.

And thanks to the design, once you put the earbuds in your ears with a little twist, they already ensure that a lot of the outside noise is blocked out. The lack of ANC is not really noticeable. The remaining noises are drowned out with the volume, if that’s what you want; the two earpieces are loud in any case.

Control Bluetooth and various codecs

Smartphones and tablets can be connected to the Sennheiser CX 400BT through Bluetooth 5.1. The association is supported by the codecs SBC, AAC and aptX, so that the clear, high-resolution sound is also transmitted 1:1 wirelessly via the drivers. Furthermore, this supports both iOS and Android devices.

What might bother one or the other is the fact that the earphones can only be connected to one device at a time. Thus, the CX 400BT are not suitable for busy entrepreneurs with multiple smartphones. What may make up for it is that the earphones can also be used independently and do not rely on each other.

In order not to have to constantly pull out the cell phone, the CX 400BT each have a touch control on the outside of the earphones. This can be individually programmed with two different functions simultaneously. The Smart Control app is helpful here, which we will get to in a separate part.

The user interface is already equipped with functions ex-works. This includes controlling the music, answering calls and activating the voice assistant of the respective device type.

Up to this point, we are absolutely satisfied with the CX 400BT from Sennheiser. The sound is good, outside noise is not significantly distracting despite the lack of ANC, and connection as well as operation are also satisfactory. Remains to be seen what microphone, battery and the app have everything on it.

Microphone gets along just fine without Transparent Hearing

Nothing earth-shattering is installed in terms of microphone technology, but it is sufficient for clear and distinct voice transmission in a typical frequency range of 100 to 10,000 Hz. All test calls in the editorial office were satisfactory. As always, however, in-ear microphones pick up a relatively large amount of background noise. Thus, it is less possible to make calls in noisy environments.

The CX 400BT’s microphone is also used for communicating with voice assistants, as should be common today. The most popular ones, such as Siri or Google Assistant, are supported. This also worked flawlessly in our tests.

The battery can last long (enough)

The power in the charging case and the in-ears is stored with the help of lithium-ion batteries. Once both earphones are fully charged, you can listen to 7 hours of music at 50 percent volume. If you have the charging box with you, the battery installed there is enough for another two charges. This extends the battery life of the earphones to a total of up to 20 hours.

A full charge here takes 1.5 hours, while you get an hour for 10 minutes. Fast and sufficient in our opinion.

The Smart Control app makes the CX 400BT more personal

The app is not a must-have to fully enjoy the features of the CX 400BT. They work just fine without it with iOS and Android devices.

But Sennheiser’s Smart Control app has an exciting feature or two up its sleeve. First of all, there is the equalizer, which allows you to tune the sound perfectly to your own ears. This can be displayed either graphically, for simplified operation, or classically with sliders.

As mentioned, the app also offers the possibility to configure the functions of the touch control panel. For this purpose, two functions each can be selected from a total of eight for the left and right earphones.

CX 400BT vs. MOMENTUM True Wireless 2

Now you would like to think that the CX 400BT can do everything that the MOMENTUM True Wireless 2 can do. According to the price, that can’t be true, and it’s not. One or the other feature is missing from the CX 400BTs and that’s why they only rank in the middle class.

Besides the lack of noise cancellation (ANC), the CX 400BT also doesn’t offer Transparent Hearing, which is the balancing of voice and ambient noise when using the microphone. Additionally, it has not been IPX certified, which makes the earphones neither water nor sweat resistant. Thus, we recommend limiting the use of the Sennheiser CX 400BT to good weather and walking pace.

All this does not detract from the sound and other quality of the Sennheiser CX 400BT. Rather, you can enjoy outstanding audio quality for 125 euros less, which has been one of the best on the market for decades. We had expected more sacrifices.


Actually, we’ve already let it slip in between that we’re completely satisfied with the Sennheiser budget earphones. For considerably less money than the MOMENTUM True Wireless 2 cost, you get the same outstanding sound quality, a satisfactory microphone, an elegant design, and the ability to personalize the CX 400BT using the Smart Control app.

The bottom line is that, in our eyes, pardon the pun, ears, an excellent product has emerged, with which Sennheiser now also puts the fear of God into the mid-range competition.

Those who can do without ANC and IPX certification should include the Sennheiser CX 400BT in the product comparison. We give it a clear buy recommendation!

Sennheiser CX 400BT

Wearing comfort
Sound quality
Value for money


The Sennheiser CX 400BT can be seen as a minimally slimmed-down version of the MOMENTUM series. However, the emphasis is on "minimal": If you can do without noise cancellation and water resistance, you get Sennheiser's high-resolution sound world played into your ears for relatively little money.

Simon Lüthje

I am co-founder of this blog and am very interested in everything that has to do with technology, but I also like to play games. I was born in Hamburg, but now I live in Bad Segeberg.

Related Articles

Leave a Reply

Back to top button