Superior sound. Tailored to you.
Your day-to-day may change but your enjoyment of superior sound won’t. Powered by Sennheiser’s leading audio technology, the new CX 400BT True Wireless gives you total control over an exceptional sound experience. With passive noise cancellation, intuitive customizable controls, long-lasting battery life and a design made for all-day comfort, they are the ideal, uncompromised choice for people that are passionate about great sound.
Premium sound. Any device.
No matter where you stand – iOS or Android – you’ll always get to enjoy the outstanding sound quality of the new CX 400BT True Wireless earbuds. Thanks to our wide range of audio codec support including SBC, AAC and aptX, premium sound is guaranteed with any mobile device.
Never miss a beat throughout the day with 20 hours of battery life – 7 hours on a single charge and a further 13 hours with the small, sleek and compact charging case. The new CX 400BT True Wireless earbuds are designed to ensure you get premium sound wherever you go.
The new CX 400BT True Wireless is made for those who enjoy diving into a long playlist, a lively audiobook or a loving phone call. Available in black and white, they have an ergonomic design created for all-day comfortable wearing. The earbuds achieve a perfect fit in the ear for excellent passive noise cancellation and keep the earbuds securely in place, thanks to adapters provided in a choice of four sizes.
Sennheiser Smart Control is a free app and compatible with most iOS and Android systems.
This app is available in 8 languages including German, English, French, Spanish, Russian, Korean, Japanese and Mandarin.
What makes the CX 400BT True Wireless so unique?
Sennheiser’s CX 400BT True Wireless is the audio specialist’s latest premium (True Wireless) Bluetooth earbuds. They deliver exceptional sound quality, optimal comfort and customizable touch controls as well as providing the best possible listening experience thanks to their ergonomic design and all-day battery life.
Designed by our audio experts, Sennheiser’s 7mm dynamic drivers ensure that the earbuds deliver outstanding stereo sound that places them in a league of their own. As well as their audiophile driver technology, this sound performance is assured by an internal audio EQ, and by the latest Bluetooth 5.1 technology, AAC and aptX compatibility.
What is the difference between CX 400BT True Wireless and MOMENTUM True Wireless 2?
The CX 400BT has many of the same amazing features of the MOMENTUM True Wireless 2. These include 7mm dynamic drivers with a built-in equalizer, an ergonomic design, customizable touch controls, calls and voice assistant access, as well as support for SBC, AAC and aptX Bluetooth codec support. The MOMENTUM True Wireless 2 adds enhanced features such as ANC & Transparent Hearing, smart pause, IPX4 splash resistance, MOMENTUM craftmanship and a 28-hour battery life, compared to 20 hours for the CX 400BT True Wireless.
Does the CX 400BT True Wireless come with the same outstanding sound signature as the MOMENTUM True Wireless 2?
Yes. The new CX 400BT True Wireless utilizes the same acoustical system as the MOMENTUM True Wireless 2. Designed by Sennheiser’s audio experts, the 7mm dynamic drivers used by this system ensures outstanding sound.
I work, commute, and travel all the time. Is the CX 400BT True Wireless a good option when on the go?
The CX 400BT True Wireless has been created to deliver the best possible sound experience at any time. The CX 400BT True Wireless features great passive sound isolation that blocks out ambient noise, an ergonomic design and all-day battery life, which make them perfect to enjoy on the go. Furthermore, effortless ease of use ensures that it is the ideal everyday audio companion!
Can the CX 400BT True Wireless block out ambient noise through ANC (Active Noise Cancellation)?
No, the CX 400BT True Wireless do not feature ANC, but they offer outstanding passive noise isolation that blocks out ambient noise thanks to their excellent fit in the ear canal. For a True Wireless model that features ANC, please see our MOMENTUM True Wireless 2 earbuds.
Does the CX 400BT True Wireless feature the latest Bluetooth technology?
Yes, the CX 400BT True Wireless is Bluetooth 5.1 compliant (class 1), ensuring a reliable and stable Bluetooth connection. The CX 400BT True Wireless features Bluetooth connections management, which makes it easy to switch between audio sources.
What Bluetooth codecs are supported by the CX 400BT True Wireless?
CX 400BT True Wireless supports current Bluetooth codecs such as SBC, AAC and aptX. Advanced audio codecs (like AAC and aptX) provide hi-fi audio that allows you to enjoy the rich uncompromised listening experience that the Sennheiser user expects.
What is the battery life of the earbuds?
CX 400BT True Wireless delivers up to 7 hours of playback time with a single earbud charge. Using the charging case, the earphones can be charged on-the-go for a total of 20 hours of playback time.
How do I charge the earbuds and carrying case?
The earbuds charge automatically once placed into the charging case. The case itself charges via a USB-C cable.
The CX 400BT True Wireless does not feature wireless charging. However, due to the 20 hours total playback time, charging of the CX 400BT True Wireless is only infrequently necessary.
Is the internal equalizer (EQ) controllable via the companion app?
Yes, the Sennheiser Smart Control app offers a very intuitive way to set up the internal EQ. Once the EQ set-up is done, all EQ parameters are stored inside the earbuds, making the personalized sound available with any music source.
Can I change the touch control assignments?
Operation is brilliantly intuitive thanks to customizable touch controls that let the user define their preferred way of controlling audio, calls or activating a preferred voice assistant like Google Assistant or Apple Siri.
Left and right earbuds may have different control assignments and can be changed easily by the Sennheiser Smart Control app.
Although customization is made easy, the default touch control assignments have been created to be a great option for users that want to control music, phones calls and voice assistance.
Can I use one single earbud as a stand-alone device?
CX 400BT True Wireless earphones deliver stereo audio via their left and right earbuds. However, the user can use the right earbud, which serves as the ‘master’ earbud to establish the connection to the paired Bluetooth device, as a stand-alone unit for phone calls and voice assistant access.
How do I access the voice assistant?
Users can activate a preferred voice assistant such as Google Assistant or Siri by a convenient touch gesture on the earbud. The voice assistant selection depends on the specific smartphone configuration. Via the Sennheiser Smart Control app, the user can customize this control to use another touch gesture for voice assistant selection or, if preferred can disable voice assistant access.
Can I connect to more than one Bluetooth device simultaneously (so-called “Bluetooth Multipoint Connection”)?
You can pair CX 400BT True Wireless with up to eight different Bluetooth devices. The CX 400BT True Wireless stores and remembers these pairings. However, you can only be connected to one device at a time, e.g. play music from one Bluetooth device.
To change from one Bluetooth device to another, connect to your second Bluetooth device by selecting the CX 400BT True Wireless entry in the Bluetooth menu (‘CX 400BT TW’).
Within the Sennheiser Smart Control app you can get an overview of the paired Bluetooth devices and manage and select your BT audio source.
Can I use the CX 400BT True Wireless without the Sennheiser Smart Control app?
Yes, you can use the CX 400BT True Wireless without the Sennheiser Smart Control app for music listening, phone calls and voice assistant access. The Smart Control app further enhances this experience by adding several additional personalization options such as adjusting the audio EQ, customizing the touch controls and selecting the voice prompt language. The Smart Control app also enables you to receive the latest firmware updates.
Are the batteries replaceable?
The batteries of the earbuds and charging case cannot be exchanged.
What ear adapters are included in the box?
The CX 400BT True Wireless comes with four sizes of silicone ear adapters (XS, S, M, L) included in the box. It is recommended to use the correct ear adapter size to form a perfect seal within the ear-canal for an optimal listening experience.
Should you wish to upgrade your CX 400BT True Wireless with foam ear adapters, Sennheiser recommends ComplyTM TrueGripTM Pro foam tips. Please visit the ComplyTM webpage for more information: https://www.complyfoam.com/
Where can I find further CX 400BT True Wireless product information?
Further information is available in a downloadable user manual, which can be found within the “Downloads” section of the CX 400BT True Wireless product page on the Sennheiser website.
What do I need to do to get the best experience once I unbox my new CX 400BT True Wireless?
• Wake up and charge the earbuds by placing them into the charging case and connecting the USB-C cable. Alternatively, after placing the earbuds into the charging case, press the button on the back of the charging case for at least 3 seconds.
• Select the correct ear adapter from a selection of four sizes (XS, S, M, L). Choose the ear adapter size that provides a very good seal in order to enjoy the best possible audio experience.
• Twist the earbuds slightly into your ear for perfect and secure fit.
• Pair the earbuds with your smartphone. The Bluetooth pairing mode is activated automatically once you first activate the earphones. Alternatively, you can manually activate pairing mode by pressing both touchpads for at least 3 seconds. In the Bluetooth menu of your smartphone, select “CX 400BT TW”.
• A voice prompt will inform you once the pairing has been completed successfully.
• Download the Sennheiser Smart Control app from your app store to personalize your CX 400BT True Wireless experience.
• For further information and support, consult the supplied quick guide or online user manual, which can be downloaded from the Sennheiser website.
What should I check or adjust to make sure the sound is at its very best?
The CX 400BT True Wireless has been created to provide exceptional sound performance, thanks to our 7 mm audiophile driver, the internal audio EQ and latest high-quality Bluetooth codecs.
However, to experience this sound to the full, it is essential to correctly place the earbuds in the ear-canal and to choose the best-fitting ear adapter set. The CX 400BT True Wireless comes with four sizes of ear adapters (XS, S, M, L) included in the box. The CX 400BT True Wireless quick guide explains precisely how to twist the earbuds into your ears to form a perfect seal within the ear-canal.
Please note that the sound may have been adjusted using the EQ function of the Smart Control app. To see if this is the case, connect to the Smart Control app and check the equalizer settings to ensure the desired sound.
What settings are recommended to get the 7-hour battery life that’s specified?
The specified battery time of 7 hours has been confirmed for music listening under the following conditions:
- CX 400BT True Wireless earbuds fully charged for at least 1.5 hours
- iPhone within 1-meter distance
- Bluetooth AAC codec
- Volume level set to 50%
- No customized EQ
The battery time may differ under different operating conditions.
How do I check for, receive and install firmware updates?
When using the Sennheiser Smart Control app, you will receive a notification once a new firmware release is available. The app will guide you through the update process. The firmware update will be installed over-the-air via the Bluetooth wireless connection.
Additionally, you can check for the current firmware release status in the Smart Control app’s settings.
Do the earbuds switch off automatically when not in use?
The CX 400BT True Wireless has integrated power-saving features. When the earbuds are disconnected from a Bluetooth source and not in use, they will switch off automatically after 15 minutes.
To turn the earphones on again, press each touch pad for more than 2 seconds.
How can I activate aptX on my Mac to receive the highest possible audio quality?
Depending on the settings, your Mac uses the SBC Bluetooth codec by default. To know which codec is active, connect your CX 400BT True Wireless to your Mac and start music playback. Press and hold the option key and click the Bluetooth menu bar icon and navigate to the CX 400BT True Wireless entry (‘CX 400BT TW’). There you will see the type of codec used currently.
If you see SBC rather than aptX, then MacOS does let you change the codec via the “Terminal” app. Open Terminal and copy in this instruction:
sudo defaults write bluetoothaudiod "Enable AptX codec" -bool true
Should you prefer to use the AAC codec, just replace “aptx” with “aac” in the above instruction.
Please note that you will need to enter your admin login data to change these settings.
How can I reset the earbuds?
If the functions of the earbuds are disturbed, you will need to perform a soft reset. A soft reset takes place each time you insert the earbuds into the charging case and wait for at least 10 seconds.
How can I perform a factory reset?
If the functions of the earbuds are disturbed and a soft reset does not fix the issue, reset the earbuds to the factory default settings. This deletes, among other settings, all pairing settings.
You can reset the earbuds to the factory default settings using the Smart Control app in the settings menu.
Alternatively, you can carry out the following steps to reset the earbuds to the factory default:
- Insert both earbuds into the charging case and wait at least 10 seconds before taking the earbuds out of the charging case and switching them on again.
- Make sure that the contacts on the earbuds and in the charging case are clean and make contact (the LED of the charging case lights up when you insert the earbuds into the charging case). If necessary, clean the contacts.
- Use the USB cable to connect the charging case to a power source.
- Insert the earbuds into the charging case and, within 30 seconds, touch and hold the right and the left touch control panel for 6 sec¬onds.
- The earphones will then be reset to their factory default settings.
What should I check if my earbuds are Bluetooth connected but music is not streamed to the earbuds?
The CX 400BT True Wireless supports two different Bluetooth connections: Bluetooth audio for all audio connections and Bluetooth LE for Sennheiser Smart Control app connection.
If your smartphone’s Bluetooth menu shows an active connection to “CX 400BT TW” and audio can’t be heard with the earbuds, but still played on the smartphone, you may have only established the Smart Control app connection.
In this case to the following steps are necessary to establish a full Bluetooth connection:
- Put both earbuds into the charging case
- Enter the Bluetooth menu of your smartphone
- Delete/Unpair all entries “CX 400BT TW” (and “LE- CX 400BT TW” if available) in the list of paired devices
- Switch off Bluetooth and activate Bluetooth again on your smartphone
(Alternatively: Reboot your smartphone)
- Take both earbuds out of the charging case
- Enter pairing mode manually by pressing both earbud touch pads for at least 3 seconds
(Pairing mode is indicated by blue/red alternating LED indicator on earbuds)
- Enter the Bluetooth menu of your smartphone and select entry “CX 400BT TW”
- The CX 400BT True Wireless will now be paired and connected with Bluetooth audio
It is recommended to first establish the Bluetooth audio connection before then connecting the Sennheiser Smart Control app. This avoids potential issues with certain smartphones.
What should I check if I can’t hear anything when using the earbuds?
Make sure that the earbuds are charged and connected to your Bluetooth device. Check that the Bluetooth settings of your connected device have media and calls connection activated. The left earbud can only be used when the right earbud is also used as the right earbud controls the Bluetooth transmission. Additionally, make sure the earbuds are inserted into your ears correctly. Increase the volume on your Bluetooth device and on the earbuds by pressing on the right earbud’s touch pad until you hear the voice prompt “Volume max”.
What should I check if I can’t pair the earbuds with my Bluetooth device?
If Bluetooth pairing does not work, proceed in the following order:
- Charge the CX 400BT True Wireless for at least 1.5 hours to ensure they are fully charged. The charging LED pulsates yellow to indicate charging and changes to a constant green to indicate they are fully charged.
- Take the earbuds out of the charging case.
- Simultaneously touch and hold the right and left touch control for 3 seconds to start pairing mode. The LED of the right earbud will flash red and blue.
- Start the search for Bluetooth devices on your smartphone and select “CX 400BT TW”.
- If necessary, enter the default pin code “0000” on your smartphone.
If, after the steps above, the Bluetooth pairing still does not work, reset the earbuds (see “How can I reset the earbuds?”).
What should I check if the LEDs on one of my earbuds are alternating green/red?
By default, the left and right earbud are peer paired to each other and connect automatically after power-on. If the LED indicator is alternating green/red, this earbud is not peer paired, i.e. the left and right earbuds are not connected to each other.
In this case perform the following steps to pair both earbuds:
- Deactivate Bluetooth in your smartphone settings to disconnect your CX 400BT True Wireless.
- Hold both touch controls for at least 10 seconds to enter peer pairing mode in both earbuds (Pairing mode is indicated by green/red alternating LED indicator on both earbuds).
- The earbuds are now being paired to each other, which may take a few seconds.
- Successful peer pairing is indicated by 3x blue flashing LEDs.
Are there reasons why the earbuds may not recharge as usual?
Ensure that the charging contacts of the earbuds and the charging case are clean. If charging is still not possible, perform a reset and a factory reset of the earbuds.
How can I adjust the earbuds to a comfortable volume or make them louder?
For some Android smartphones there is a separate volume control for the Bluetooth headset and for the Android smartphone. Ensure that both volume controls are set to max. To increase volume, tap and hold the touchpad of the right earbud until you hear the voice prompt “Volume max”. Now increase the smartphone’s volume to maximum volume.
For smartphones that feature “absolute volume control” such as the Apple iPhone, there is only one volume control available, so you can either use the volume control of the smartphone or that of the CX 400BT True Wireless. With a few smartphones “absolute volume control” is not available by default but can be activated within the development options.
Furthermore, you might not be able to perceive the full volume of the CX 400BT True Wireless because the earphones currently do not fit correctly. Please use the appropriate size of ear adapters so they fit snugly in your ear canal and completely seal your ears. For best results, follow the quick guide on how best to place the earbuds into your ears.
During the OTA firmware update an error occurred?
In case you experience any issues during the OTA firmware update of your CX 400BT True Wireless, please follow the following steps:
-Insert both earbuds into the charging case for at least 10 seconds
-Take the earbuds out of the charging case and connect them again to the Sennheiser Smart Control app
-Repeat the OTA FW update or follow the instructions provided by the app
Why do I see only one battery level for both earbuds in the Sennheiser Smart Control app?
The battery level indicator always shows the remaining battery life of the earbud side with less power.
- If left earbud has 50% battery level and right earbud has 80% battery level, it indicates 50% battery level.
- If left earbud has 90% battery level and right earbud has 20% battery level, it indicates 20% battery level.
- If only right earbud is in use and left earbud remains in the charging case, it indicates the right earbud battery level.
When watching video or gaming on my device is there a recommended way to ensure the sound is in sync with the visuals?
Perfect synchronization of sound and image is dependent on the Bluetooth technology being used by your Bluetooth device. For best results make sure you are using a Bluetooth device which fully supports Audio Video Distribution Transport Protocol (AVDTP) 1.3 or higher. Thus, depending on the Bluetooth device or the mobile app the audio/video synchronization experience may vary. It is recommended to use always the latest software for your Bluetooth device or the mobile apps.
How can I ensure the best fit for the earbuds?
It’s always best to test the supplied ear adapters to find the size that suits you best and delivers the best sound quality. The CX 400BT True Wireless packaging includes four different ear adapter sizes (XS, S, M, L). Also try to twist the earbuds into your ear as described in the quick guide until you find a comfortable position.
Why is it vital to stay in my device’s range to prevent sound drop-outs?
Make sure that the earbuds are within the transmission range of the Bluetooth device. Since the right earbud establishes the connection to the smartphone, the transmission can be more reliable when your Bluetooth device is placed on the right side of your body.
What should I consider if I have issues connecting my smartphone with the Smart Control app?
A very small number of smartphone models may have issues connecting the Smart Control app to the CX 400BT True Wireless. Future app and firmware updates will improve on potential limitations of this nature.
You may try to turn off and turn on the Bluetooth function on your smartphone to reset the Bluetooth module or reboot the smartphone.
You may also try the following: Go to the smartphone’s security and location settings and turn “use location” off and on again, even if the location service is already turned on. This is because some Android models require that the location service is activated when using Bluetooth Low Energy connection, even when the location information is not used. Sennheiser does not use or store location information of the user for other reasons.
You may also perform a factory reset of the CX 400BT True Wireless. Disconnect the CX 400BT True Wireless after the factory reset, i.e. remove entries CX 400BT TW (and LE- CX 400BT TW if available) in the Bluetooth settings of your smartphone and pair CX 400BT True Wireless again.
How do I ensure my voice is picked up clearly during phone calls?
If you find that your voice can’t be heard well by the other party on a phone call, you may wish to check the following: During phone calls, ensure that the earbuds are inserted correctly into the ear-canal and then rotate them slightly. Ideally rotate the earbud to ensure the correct beamforming angle for voice pickup (i.e. both mics in line to the mouth). Please also check that the microphone opening is not blocked by the ear itself.
Additionally, wind may sometimes impact the quality of the phone call.
Which spare parts are available for my CX 400BT True Wireless?
The following spare parts and accessories for the CX 400BT True Wireless are available:
For the Black color variant of the CX 400BT True Wireless (CX400TW1 Black):
• Charging case (CX400TW1 C Black) : Order No. 508906
For the White color variant of the CX 400BT True Wireless (CX400TW1 White):
• Charging case (CX400TW1 C White) : Order No. 508907
Replacements of silicone ear adapters are only available in black color (fits CX 400BT True Wireless color variants):
• Set of 10 ear adapters (size XS) : Order No. 508603
• Set of 10 ear adapters (size S) : Order No. 508604
• Set of 10 ear adapters (size M) : Order No. 508605
• Set of 10 ear adapters (size L) : Order No. 508606
Further information on accessories and spare parts can be found on Sennheiser’s CX 400BT True Wireless product page in the section “Related products - Accessories”.
How can I contact the Sennheiser service department?
Contact information of your Sennheiser service partner can be found here: