The CX 400BT come with mobile app support too via the Sennheiser Smart Control app, which supports other Sennheiser headphones such as the HD 350BT and HD 450BT. The app currently has a low star rating, which based on the reviews seems to do with a recent firmware upgrade, although no issues were found during the review. The app does require access to the phone's location in order to work and the phone has to be running Android (8 and higher) or iOS (13 and higher).
The Sennheiser Smart Control app interface is intuitive and user friendly as there is no account sign up required, other than agreeing to the app's privacy policy, which also includes sending data from your phone anonymously (this is optional). The app features two types of sound equalizer - a wave equalizer and a slider equalizer with bass, mids and treble adjustment sliders.
The wave equalizer is controlled by dragging your finger on the screen until you get the desired sound curve signature. There is no built-in presets but, you can create multiple presets to store different sound signatures.The settings get stored inside the earbuds, which is convenient. The app also displays a battery indicator but, it only feedbacks the battery status of the earbud with less battery charge.
The Sennheiser CX 400BT fully charge in 1.5 hours (via 5V/600mA) and, there is quick charge support so, you can get 60 minutes worth of playtime from a 10 minute recharge. The charging case can hold around 13 hours of extra charge. Without customizing the EQ and with volume set to 50%, you can achieve the stated 7 hours battery life. At 70% volume, you get a runtime of 6 hours.
The Sennheiser Smart Control app also lets you remap the touch control functions from a maximum of six functions per earbud (including answer and reject calls). The functions are controlled via a single tap, double tap, triple tap and long press.
By default, the volume is set to long press, which is the best way to increase and decrease volume on true wireless. Of course, you can change this to a tap if you want to. Functions include voice assistant, play/pause, calls and skipping tracks. You can even disable touch controls and change voice prompts to a beep tone. There is a voice prompt when reaching max volume.
The CX 400BT don't have IPX rating, which is strange. And, there is only one microphone, which it's also strange because most true wireless earbuds on the market are dual mics with one microphone per earbud, which is nice because it allows you to take calls with either earbud. The CX 400BT microphone is located on the front touch control panel of the right earbud and delivers clear sound, although because of its location it is prone to wind noise.
Both the CX 400BT charging case and earbuds have a tall, square body; hence they are bulky looking and they will bulge out of your ears. Despite the size though, the CX 400BT earbuds are no heavier than the average true wireless and they surprisingly fit much more comfortably than a lot of true wireless. The included silicone eartips play an important part in the comfort as they aren't run-of -the-mill. They are made of soft silicone and have a wide bore with a crosshair design that helps maintain the shape of the tip inside the ear canal.
The CX 400BT earbuds measure 1.5cm tall and 1.5cm wide and weigh 13 grams (6.5 grams each). The front panel, which integrates the touch control, has a reflective glossy finish. The earbuds have a short stubby nozzle neck with a filter mesh tucked inside the narrow tip. The volume output is not the loudest but the superb passive isolation makes up for it. The charging case measures 4cm high, 5.5cm wide and 3cm thick and weighs 37 grams (without the earbuds). On the back of the charging case, there is the USB-C charging port, a battery status led and a button next to it to activate it.
The CX 400BT charging case has a smooth matte coat finish with round corners and a chrome Sennheiser logo on top. The plastic hinge supporting the lid opens up upright, revealing the earbuds, which are easy to remove from the charging dock. The earbuds are held securely via the magnets inside the charging case.
On the underside of the earbuds, there are two small gold plated contacts (for charging), two metal contacts and a status led. The location of the status led means nobody around you will be seeing a blinking light when you're listening to audio. On the downside, you cannot tell when the earbuds are fully charged inside the charging case.
Having a large body does have its upside though, and that is better sound. The 7mm dynamic drivers are able to generate very good bass and broad soundstage that allows a good separation between the midrange and treble. Sennheiser has tuned the CX 400BT similarly to the Momentum True Wireless 2 so, the CX 400BT and Momentum True Wireless 2 are similarly sounding, which is interesting considering the huge price difference. That said, the Momentum True Wireless 2 earbuds do integrate active noise cancellation (ANC), which is one reason for the bump in price. If you don't need ANC, the CX 400BT is the more affordable choice plus, it delivers good passive noise isolation at 70% volume (and above) for blocking noises.
The Bluetooth 5.1 chip supports SBC, AAC and aptX but, it does not support multipoint connection pairing. Initial pairing is straightforward and requires having to take the earbuds out of the charging case; hence bluetooth pairing isn't automatically activated when opening the charging case lid. When switching from mono listening to stereo there is a long re-connection delay (up to 6 seconds).
Also, when the right earbud is put into the charging case the audio in the left earbud pauses automatically, which makes the switching experience between earbuds not as seamless as other earbuds. Accessories included are different size ear tips and a short Sennheiser branded charging cable. You can buy the Sennheiser CX 400BT from Amazon. Check out the new GTW 270 earbuds
Having a large body does have its upside though, and that is better sound. The 7mm dynamic drivers are able to generate very good bass and broad soundstage that allows a good separation between the midrange and treble. Sennheiser has tuned the CX 400BT similarly to the Momentum True Wireless 2 so, the CX 400BT and Momentum True Wireless 2 are similarly sounding, which is interesting considering the huge price difference. That said, the Momentum True Wireless 2 earbuds do integrate active noise cancellation (ANC), which is one reason for the bump in price. If you don't need ANC, the CX 400BT is the more affordable choice plus, it delivers good passive noise isolation at 70% volume (and above) for blocking noises.
The Bluetooth 5.1 chip supports SBC, AAC and aptX but, it does not support multipoint connection pairing. Initial pairing is straightforward and requires having to take the earbuds out of the charging case; hence bluetooth pairing isn't automatically activated when opening the charging case lid. When switching from mono listening to stereo there is a long re-connection delay (up to 6 seconds).
Also, when the right earbud is put into the charging case the audio in the left earbud pauses automatically, which makes the switching experience between earbuds not as seamless as other earbuds. Accessories included are different size ear tips and a short Sennheiser branded charging cable. You can buy the Sennheiser CX 400BT from Amazon. Check out the new GTW 270 earbuds