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Sennheiser CX 400BT True Wireless Owner Manual

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Sennheiser CX 400BT True Wireless Owner Manual


Product overview

Charging case


  1. LED displays the charging process/charge status of the rechargeable battery of the charging case or of
    the earbuds (when inserted into the charging case)
  2. Input for USB-C connector for charging the rechargeable batteries
  3. LED button activates the LED display for 5 seconds
  4. Built-in rechargeable battery for charging the earbuds on the go
  5. Type plate
  6. Charging compartment for the left earbud L
  7. Magnetic holders
  8. Charging compartment for the right earbud R
  9. Charging contacts
  10. Sennheiser-CX-400BT-True-Wireless-image-2Touch control panel
  11. Changeable silicone ear adapters
  12. Left earbud L (secondary earbud, receives signals from the right earbud)
  13. Status LED
  14. Magnetic holders
  15. Charging contacts
  16. Microphones for phone calls
  17. Right earbud R (primary earbud, controls the Bluetooth connection to the smartphone and to the left
  18. Openings for acoustic optimization
  19. Built-in rechargeable battery

Using the earphones

Information on the rechargeable battery, the charging process and the first use.The earbuds and the charging case each have a built-in rechargeable battery. The charging case allows you to store the earbuds safely at all times while they are being charged.Upon delivery, the rechargeable batteries of the earbuds and the charging case are in sleep mode and have to be woken up by connecting them to a power source once. Sennheiser recommends charging the earbuds and the charging case for a complete charging cycle without interruption before using for the first time.A complete charging cycle of the charging case and the earbuds takes about 1.5 hours. The quick charge function gives you approx. 1 hour of playback time after 15 minutes of charging.

Charging the rechargeable battery of the earbuds and the charging case


  1. Open the charging case by overcoming a slight magnetic resistance and insert the left earbud into the left charging compartment and the right earbud into the right charging compartment.
  2. Connect the USB-C connector of the USB cable to the USB-C socket of the charging case.
  3. Connect the USB-A connector to a corresponding socket of a USB power source (to be ordered separately). Make sure that the USB power source is connected to the power supply system.The rechargeable batteries of the earbuds and the charging case are being charged.

The LED of the charging case displays the charge status:


Care and maintenance of the earbuds/charging case

Liquids can damage the electronics of the product!
Liquids entering the housing of the product can cause a short-circuit and damage the electronics.

  • Keep all liquids far away from the product.
  • Do not use any solvents or cleansing agents.
  • Clean the product only with a soft, dry cloth.
  • You can clean the silicone ear adapters under lukewarm running water. Allow the ear adapters to dry at room temperature for at least 12 hours before putting them back on the earbuds.
  • Clean the charging contacts on the earbuds and in the charging case from time to time using e.g. a cotton swab.


Replacing the ear adapters

For reasons of hygiene, you should replace your ear adapters from time to time. Spare ear adapters are available from your Sennheiser partner.

  1.  Pull the ear adapter away from the in-ear sound tunnel.
  2.  Mount the new ear adapter to the in-ear sound tunnel. Ensure that it locks into place.



Wearing styletrue wireless stereo earphones
Ear couplingear-canal, closed-back
Frequency response5 Hz to 21 kHz
Transducer principledynamic
Transducer size7 mm
Sound pressure level (SPL)114 dB (1 kHz/0 dBFS)
THD (1 kHz, 94 dB SPL)< 0.08 %
Microphone principleMEMS
Microphone frequency response100 Hz to 10 kHz
Microphone pick-up pattern (speech)2-mic beamforming array
Power supplybuilt-in Lithium rechargeable batteries, 3.7 V

earbuds: 54-60 mAh charging case: 400-420 mAh

USB charging via USB-C socket of the charging case: 5 V , 600 mA

Operating time7 hrs with rechargeable battery of the earbud (test conditions: iPhone within 1 m distance, Bluetooth AAC codec, volume level 50 %, no EQ settings); 20 hrs with rechargeable battery of the charging case
Charging time of rechargeable batteriesapprox. 1.5 hrs
Temperature rangeoperation: 0 to +40°C

storage: –25 to +70°C

Relative humidityoperation: 10 to 80%, non condensing

storage: 10 to 90%

Magnetic field strengthearbuds: 0.63 mT charging case: 101 mT
Weightearbuds: approx. 6 g each charging case: approx. 37 g



VersionBluetooth 5.1 compatible, class 1, BLE
Transmission frequency2,402 MHz to 2,480 MHz
ModulationGFSK, π/4 DQPSK, 8DPSK
Output power10 mW (max)
CodecaptX®, AAC, SBC


Device nameCX 400BT TW

LE-CX 400BT TW (Bluetooth Low Energy only)

Number of active connections1


Manufacturer Declarations


Sennheiser electronic GmbH & Co. KG gives a warranty of 24 months on this product.For the current warranty conditions, please visit our website at or contact your Sennheiser partner.

In compliance with the following requirements
  • General Product Safety Directive (2001/95/EC)
  • Compliant to Sound Pressure Limits according to country specific requirements


Sennheiser is a registered trade mark of Sennheiser electronic GmbH & Co. KG. Apple and the Apple logo are trademarks of Apple Inc., registered in the U.S. and other countries. App Store is a service mark of Apple Inc.Google Play and the Google Play logo are trademarks of Google LLC.The Bluetooth® word mark and logos are registered trademarks owned by Bluetooth SIG, Inc. and any use of such marks by Sennheiser electronic GmbH & Co. KG is under license. Qualcomm aptX is a product of Qualcomm Technologies International, Ltd. Qualcomm is a trademark of Qualcomm Incorporated, registered in the United States and other countries, used with permission.




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