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If the functions of the earbuds are disturbed, you will need to perform a reset. Placing both earbuds into charging case then press the touch controls for at least 5 sec will soft reset both earbuds.
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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.
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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.
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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".
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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 permanent 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 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, restart the earbuds (see “How can I reset the earbuds?”).
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.
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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.
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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.
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In case you experience any issues during the OTA (Over The Air) 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
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The battery level indicator always shows the remaining battery life of the earbud side with less power.
Examples:
• 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.
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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.
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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.
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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.
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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.
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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.
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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):
•Left earbud (CX400TW1 L Black) : Order No. 508904
•Right earbud (CX400TW1 R Black) : Order No. 508902
•Charging case (CX400TW1 C Black) : Order No. 508906
For the White color variant of the CX 400BT True Wireless (CX400TW1 White):
•Left earbud (CX400TW1 L White) : Order No. 508905
•Right earbud (CX400TW1 R White) : Order No. 508903
•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".
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Contact information of your Sennheiser service partner can be found here:
https://en-us.sennheiser.com/service-support-contact-center