CX 400BT True Wireless
True wireless stereo earphones
Model: CX400TW1, CX400TW1 R, CX400TW1 L, CX400TW1 C
Instruction manual
Use the search function, the navigation (left) or the following links:
Start
“Product overview”
“Getting started”
“Using the earphones”
“FAQ/If a problem occurs ...”
“Specifications”
Sennheiser electronic GmbH & Co. KG
Am Labor 1
30900 Wedemark
Germany
www.sennheiser.com
Version: 11/20 A03
Important safety instructions
2 | CX 400BT True Wireless
Important safety instructions
▷ Read this instruction manual carefully and completely before
using the product.
▷ Always include this instruction manual when passing the product
on to third parties.
▷ Do not use the product if it is obviously defective or makes loud,
unusual (whistling or beeping) noise.
▷ Only use the product in environments where Bluetooth® wireless
transmission is permitted.
Preventing damage to health and accidents
▷ Protect your hearing from high volume levels. Permanent
hearing damage may occur when headphones are used
at high volume levels for long periods of time. Sennheiser
headphones sound exceptionally good at low and medium volume
levels.
▷ Do not insert the earphones too deep into your ears and never
insert them without ear adapters. Always remove the earphones
slowly and carefully from your ears.
▷ The product generates stronger permanent magnetic
fields that could cause interference with cardiac pace-
makers, implanted defibrillators (ICDs) and other
implants. Always maintain a distance of at least 3.94"/10 cm
between the product component containing the magnet (earbuds
and charging case) and the cardiac pacemaker, implanted
defibrillator, or other implant.
▷ Keep the product, accessories and packaging parts out of reach
of children and pets to prevent accidents. Swallowing and chok-
ing hazard.
▷ Do not use the product in an environment that requires your spe-
cial attention (e.g. in traffic).
Preventing damage to the product and malfunctions
▷ Always keep the product dry and do not expose it to extreme tem-
peratures (hairdryer, heater, extended exposure to sunlight, etc.)
to avoid corrosion or deformation. The normal operating tempera-
ture is from 0 °C to 40 °C/32 °F to 104 °F.
▷ Use only attachments/accessories/spare parts supplied or rec-
ommended by Sennheiser.
▷ Clean the product only with a soft, dry cloth.
Safety instructions for Lithium rechargeable batteries
WARNING
If abused or misused, the rechargeable batteries may leak.
In extreme cases, they may even present a risk of:
•explosion,
• fire development,
• heat generation,
•smoke or gas development.
Important safety instructions
CX 400BT True Wireless | 3
Notes on data collection and processing and on firmware updates
This product stores individual settings such as the volume, the
sound profiles and the Bluetooth connection data of paired devices.
This data is required for the operation of the product and is not trans-
ferred to Sennheiser or companies commissioned by Sennheiser and
is not processed.
Using the “Sennheiser Smart Control” app, you can update the firm-
ware of the product for free via an Internet connection. If the device
on which the app is installed is connected to the Internet, the follow-
ing data is automatically transferred to and processed by Sennheiser
servers in order to provide and transfer suitable firmware updates:
hardware identifier, hardware revision number, firmware version of
the product, operating system type (Android, iOS) and version, ver
-
sion of the app. The data will only be used as specified and will not
be stored permanently.
If you do not want this data to be transferred and processed, do not
connect to the Internet.
Intended use/Liability
These headphones have been designed as an accessory for Blue-
tooth compliant devices. They are intended for wireless audio com-
munication such as music playback and phone calls via Bluetooth
wireless technology.
It is considered improper use when the product is used for any appli-
cation not named in the corresponding product documentation.
Sennheiser does not accept liability for damage arising from misuse
or improper use of this product and its attachments/accessories.
Sennheiser is not liable for damages to USB devices that are not con-
sistent with the USB specifications. Sennheiser is not liable for dam-
ages resulting from the loss of connection due to flat or overaged
rechargeable batteries or exceeding the Bluetooth transmission
range.
Before putting into operation, please observe the respective coun-
try-specific regulations.
Only use rechargeable batteries and chargers
recommended by Sennheiser.
Only charge the product / rechargeable batteries at
ambient temperatures between 10 °C to 40 °C/50 °F to
104 °F.
Do not heat the product / rechargeable batteries above
70 °C/140 °F. Avoid exposure to sunlight and do not
throw the product / rechargeable batteries into fire.
When not using the product / rechargeable batteries for
extended periods of time, charge them regularly (about
every three months).
Switch rechargeable battery-powered products off after
use.
Dispose of defective products with built-in rechargeable
batteries at special collection points or return them to
your specialist dealer.
Package contents
4 | CX 400BT True Wireless
Package contents
Online you can find:
• this detailed instruction manual and additional information
(www.sennheiser.com/download
)
• the Sennheiser Smart Control app for configuring the head-
phones and for additional functions
(www.sennheiser.com/smartcontrol)
Earbud R for right ear (CX400TW1 R) and
earbud L for left ear (CX400TW1 L)
Charging case with built-in rechargeable battery for
the earbuds (CX400TW1 C)
USB charging cable with USB-C and
USB-A connector, approx. 0.25 m
Silicone ear adapters (size XS, S, M (pre-mounted to
the earbuds) and L)
Quick guide
Safety guide
A list of accessories can be found on the CX 400BT True Wire-
less product page at www.sennheiser.com .
Contact your local Sennheiser partner: www.sennheiser.com
>
“Service & Support”.
Product overview
CX 400BT True Wireless | 5
Product overview
Charging case
CX400TW1 C
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)
Input for USB-C connector
for charging the rechargeable batteries
LED button
activates the LED display for 5 seconds
Built-in rechargeable battery for charging the earbuds on
the go
Type plate
Charging compartment for the left earbud L
Magnetic holders
Charging compartment for the right earbud R
Charging contacts
1
2 3
4
5
7
8
6
7
9
Product overview
6 | CX 400BT True Wireless
Earphones
CX400TW1 R and CX400TW1 L
Touch control panel
Changeable silicone ear adapters
Left earbud L (secondary earbud, receives signals from the
right earbud)
Status LED
Magnetic holders
Charging contacts
Microphones for phone calls
Right earbud R (primary earbud, controls the Bluetooth
connection to the smartphone and to the left earbud)
Openings for acoustic optimization
Built-in rechargeable battery
Product overview
CX 400BT True Wireless | 7
Overview of the LED indications of the
charging case
When a USB cable is connected, the LED of the charging case per-
manently displays the charging process:
If you press the LED button and no USB cable is connected, the LED
of the charging case displays the battery charge status or the
charging process of the earbuds for 5 seconds:
LED
Charging case WITH
earbuds inserted
Charging case
WITHOUT earbuds
inserted
pulses
yellow
... earbuds and
charging case are
being charged
... charging case is
being charged
lights up
green
... earbuds and
charging case are
fully charged
... charging case is
fully charged
flashes
red
... a charging error/
battery error has
been detected in at
least one earbud (>
30)
... a charging error/
battery error has
been detected in the
charging case (> 30)
1x
Product overview
8 | CX 400BT True Wireless
Overview of the LED indications of the
earbuds
LED
Charging case WITH
earbuds inserted
Charging case
WITHOUT earbuds
inserted
lights up
green
... earbuds are fully
charged and the
charging case can
still charge at least
one complete cycle
... charging case is
fully charged
pulses
yellow
... earbuds are being
charged via the
rechargeable bat-
tery of the charging
case
–
lights up
yellow
... earbuds are fully
charged, the
charging case
cannot charge
another complete
cycle
... charging case is
charged less than 90
%
lights up
red
... rechargeable bat-
teries of the earbuds
and the charging
case are empty
... rechargeable bat-
tery of the charging
case is empty
flashes
red
... a charging error/
battery error has
been detected in at
least one earbud (>
30)
... a charging error/
battery error has
been detected in the
charging case (>
30)
If the LED does not light up:
• Clean the contacts on the earbuds and in the charging case
(> 29).
• Charge the rechargeable batteries of the earbuds and the
charging case until the LED lights up again (> 14).
Product overview
CX 400BT True Wireless | 9
Notes on voice prompts
The earphones output voice prompts for events (the table gives
some examples). Using the Smart Control app, you can change the
language of the voice prompts, choose between voice prompts and
beep sounds, or deactivate the status messages with a few excep-
tions (e.g. rechargeable battery is empty).
LED Meaning; the earbuds...
flashes red-blue
for approx. 1
minute
... are in Bluetooth pairing mode
flashes blue 3x
... Bluetooth pairing or earbud pair-
ing successful
flashes red 3x
... Bluetooth pairing or earbud pair-
ing failed
lights up blue
... are connected to a device via
Bluetooth
(primary earbud (R) is connected to
the smartphone, secondary earbud
(L) is connected to the primary
earbud (R))
lights up red
... are not connected to a device via
Bluetooth or the connection has
been lost
(primary earbud (R) is not connected
to a smartphone, secondary earbud
(L) is not connected to the primary
earbud (R))
flashes red
quickly
... rechargeable battery is almost
empty
flashes red
slowly
... system error – the Smart Control
app may display details. Perform a
restart (> 31)
flashes red-
green for
approx. 1 minute
... are in earbud pairing mode (to pair
the right and left earbud)
3x
3x
Voice prompt Meaning/earbuds...
“Power on” ... are switched on
“Power off” ... switch off
“Connected” ... connected via Bluetooth
“No connection” ... not connected via Bluetooth
“Pairing” ... in Bluetooth pairing mode
“Pairing cancelled” ... Bluetooth pairing cancelled
“Pairing successful” ... Bluetooth pairing successful
“Pairing failed” ... Bluetooth pairing not successful
Product overview
10 | CX 400BT True Wireless
“Recharge headset” ... Rechargeable battery is almost
empty. Recharge the rechargeable
battery.
“Call rejected” ... incoming call rejected
“Call ended” ... call ended
“Volume min” ... volume set to minimum
“Volume max” ... volume set to maximum
Voice prompt Meaning/earbuds...
Getting started
CX 400BT True Wireless | 11
Getting started
1. Waking up the earbuds and the charging case
and charging the rechargeable batteries
Upon delivery, the rechargeable batteries of the earbuds and the
charging case are in sleep mode and have to be woken up by con-
necting them to a power source once.
▷ Insert the earbuds into the charging case.
▷ Connect the USB-C cable to the charging case and to a USB
power source (> 14).
The earbuds and the charging case are woken up and the
rechargeable batteries are being charged. The earbuds are now
ready for use.
Alternatively:
▷ Press and hold the LED button on the charging case for 3 sec-
onds.
The earbuds and the charging case are woken up and can now be
used.
2. Selecting suitable ear adapters for optimum
fit of the earbuds
The perceived sound quality including bass performance and the
best possible noise cancellation of the earphones depends to a large
extent on the correct fit of the earbuds in the ear.
▷ Test which ear adapter size gives you the best sound quality and
the best wearing comfort.
L
R
USB-A
USB-C
LMSXS
R
L
Getting started
12 | CX 400BT True Wireless
▷ You can choose between 4 different ear adapters in size XS, S, M
and L (> 20).
▷ Assign the right earbud to your right ear and the left earbud to
your left ear.
▷ Insert the earbuds at a slight angle into the ears and twist them
slightly into the ear canal so that they sit comfortably and snugly
in the ear canal.
3. Connecting the earphones to a Bluetooth
device
Connect the earphones to your smartphone via Bluetooth (> 16).
4. Installing the Smart Control app on your
smartphone
The Sennheiser Smart Control app allows you to use all functions
and settings of the earphones and to e.g. adjust the sound to your
liking using the equalizer (> 19).
RightLeft
R
L
1
3s
L
R
“Pairing“
“Sennheiser Smart Control”
Using the earphones
CX 400BT True Wireless | 13
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 con-
necting 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.
Sennheiser recommends using the supplied USB cable and a com-
patible standard USB power supply for charging the headphones.
When a USB cable connected to a power source is also connected to
the charging case, the rechargeable battery of the charging case is
being charged. When the earbuds are inserted into the charging box,
their rechargeable batteries are being charged at the same time. The
LED of the charging case displays the charge status (>
7).
When the battery charge of the earbuds drops to a critical level, a
voice prompt asks you to recharge the earbuds (“Recharge head-
set”).
The charge status of the rechargeable battery of the charging case
is displayed by the LED on the charging case (> 7).
Rechargeable
battery
Operating time with fully charged
rechargeable batteries
Earbuds
approx. 7 hrs (test conditions: iPhone within 1
m distance, Bluetooth AAC codec, volume
level 50 %, no EQ settings)
Earbuds and
charging case
approx. 20 hrs (approx. 2 additional charging
cycles of the earbuds via the charging case)
Using the earphones
14 | CX 400BT True Wireless
Charging the rechargeable battery of the
earbuds and the charging case
1. Open the charging case by overcoming a slight magnetic resis-
tance and insert the left earbud into the left charging compart-
ment and the right earbud into the right charging compartment.
The earbuds are magnetically pulled into the charging compart-
ments.
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.
If no earbuds are inserted into the charging case, only the
rechargeable battery of the charging case is being charged.
The LED of the charging case displays the charge status:
LED
Charging case WITH
earbuds inserted
Charging case
WITHOUT earbuds
inserted
pulses
yellow
... earbuds and
charging case are
being charged
... charging case is
being charged
lights up
green
... earbuds and
charging case are
fully charged
... charging case is
fully charged
flashes
red
... a charging error/
battery error has
been detected in at
least one earbud (>
30)
... a charging error/
battery error has
been detected in the
charging case (> 30)
L
R
1 2
USB-A
USB-C
3
Using the earphones
CX 400BT True Wireless | 15
Connecting the earphones to a Bluetooth
device
To be able to use the Bluetooth wireless connection, you must regis-
ter both devices (earphones and e.g. smartphone) via the device set-
tings of your smartphone. This process is called pairing.
If operation differs from the steps mentioned, also refer to the
instruction manual of the Bluetooth device you are using.
Information on the Bluetooth wireless
connection
The earphones are compatible with Bluetooth 5.1.
If your audio source supports one of the following high-resolution
audio encoding methods, music is automatically played in high audio
quality: aptX® or AAC. Otherwise the headphones will play your
music in normal audio quality (SBC).
Paired devices establish the Bluetooth wireless connection immedi-
ately after switch-on and are ready for use.
When you switch the earphones on, they automatically try to con-
nect to the last connected Bluetooth device. The earphones can save
the connection profiles of up to eight Bluetooth devices with which
they have been paired. Audio playback is only possible from one
device at a time.
If you pair the earphones with the ninth Bluetooth device, the saved
connection profile of the least used Bluetooth device will be over-
written. If you want to re-establish a connection with the overwritten
Bluetooth device, you have to pair the earphones again.
Using the Smart Control app, you can view the list of paired devices
and selectively connect and disconnect devices (“Connections”; >
17).
When you switch on the earphones for the first time after initial
charging, they automatically switch to pairing mode.
Paired and connected Bluetooth device
Paired Bluetooth device (currently not connected)
Using the earphones
16 | CX 400BT True Wireless
Pairing the earphones with a Bluetooth
device
1. Take both earbuds out of the charging case and insert them into
your ears (> 20). The distance between the earbuds and the Blue-
tooth device should not exceed 40"/1 m.
2. Simultaneously touch and hold the right and the left touch control
panel for 3 seconds until you hear the voice prompt “Pairing” and
a beep.
The LEDs of the earbuds flash blue and red. The earbuds are in
pairing mode.
3. Activate Bluetooth on your Bluetooth device.
4. Via the menu of your Bluetooth device, start the search for new
Bluetooth devices.
All active Bluetooth devices in the proximity of your smartphone
are displayed.
From the list of found Bluetooth devices, select “CX 400BT TW”.
If necessary, enter the default pin code “0000”.
If pairing was successful, you hear the voice prompt “Pairing suc-
cessful” and the LEDs of the earbuds flash blue 3x.
The right and the left earbud also use a Bluetooth wireless con-
nection. Both earbuds are paired with each other upon delivery.
If you are using a different earbud (e.g. a spare earbud), the two
earbuds must also be paired with each other (> 17).
If no connection is established within 1 minute, pairing mode is
terminated and the earbuds switch to idle mode. If necessary,
repeat the steps described above.
If the earphones are not paired with any Bluetooth device (the
pairing list is empty), pairing mode is permanently active.
max. 1 m/40 inch
ON
CX 400BT TW
*********
************
1
3 4
2
3s
3x
“Pairing“
“Pairing
successful“
Using the earphones
CX 400BT True Wireless | 17
Switching the connection to paired
Bluetooth devices/“Connections”
To selectively switch the audio connection to paired Bluetooth
devices using the “Connections” function, you require the Smart
Control app (> 19).
▷ In the Smart Control app, tap “Connections”.
The list of Bluetooth devices paired with the earphones appears.
▷ From the list, select the paired device to which you want to con-
nect the earphones. Make sure that the desired device is
switched on and Bluetooth is activated.
The Bluetooth audio connection between the desired Bluetooth
device and the earphones is established.
The app connection between the device with the Smart Control
app installed and the earphones remains active (only Bluetooth
Low Energy for communication between app and earphones, the
device name is highlighted in bold).
Disconnecting the earphones from a
Bluetooth device
▷ Via the menu of your Bluetooth device, disconnect the connection
to the earphones.
The earphones are disconnected from the Bluetooth device. The
earphones then search for other paired devices. If no device is
found, you hear the voice prompt “No connection”. The head-
phones switch to idle mode.
Pairing the earbuds with each other
(optional)
The right and the left earbud are paired with each other upon deliv-
ery. If, however, you are using a different earbud (e.g. a spare ear-
bud), you have to pair the two earbuds with each other once:
1. Make sure that the right earbud is not connected to any Bluetooth
device. Deactivate Bluetooth on your Bluetooth device or delete
“CX 400BT TW” from the list of paired devices in the menu of your
Bluetooth device.
2. Charge the right and the left earbud (> 14).
3. Take both earbuds out of the charging case and make sure that
the right and the left earbud are close together (max. distance
50 cm).
The LEDs of the earbuds light up red.
Using the “Connections“ function in the Smart Control app, you
can also selectively connect the earphones to paired devices
without terminating an existing connection (> 17).
If you want to clear the Bluetooth pairing list of the earphones,
reset the earphones to the factory default settings (> 32).
Using the earphones
18 | CX 400BT True Wireless
4. Simultaneously touch and hold the right and the left touch control
panel for 10 seconds until you hear the voice prompt “Pairing” and
a beep.
The LEDs of the earbuds flash green and red. The earbuds are in
earbud pairing mode.
If pairing was successful, you hear the voice prompt “Pairing suc-
cessful” and the LEDs of the earbuds flash blue 3x.
▷ Now pair the earbuds with your Bluetooth device (> 16).
1
3 4
2
“Pairing
successful“
“Pairing“
LR
max. 50 cm
Bluetooth off
USB-A
USB-C
Hold 10s
3x
Using the earphones
CX 400BT True Wireless | 19
Installing the Smart Control app
To make full use of all the settings and functions of the headphones,
you need to have the free Sennheiser Smart Control app installed on
your smartphone.
Download the app from the App Store or Google Play and install it on
your smartphone. Alternatively, you can use your smartphone to
scan the following QR code or to call up the following Internet site:
www.sennheiser.com/smartcontrol
▷ Connect your smartphone to the earphones using Bluetooth (>
15).
▷ Start the Smart Control app.
▷ Follow the instructions in the app.
▷ Simultaneously touch and hold the right and the left touch control
panel for 3 seconds to accept the Bluetooth Low Energy connec-
tion.
The Smart Control app recognizes the earphones and activates
all available settings and functions.
If you connect the earphones via the Smart Control app, only a
Bluetooth Low Energy connection may be established (Blue-
tooth name “LE-CX 400BT TW”). To use the earphones for
music playback, etc., pair the earbuds via the Bluetooth menu
of your smartphone (Bluetooth name “CX 400BT TW”) (> 16).
“Sennheiser Smart Control”
Using the earphones
20 | CX 400BT True Wireless
Selecting suitable ear adapters for
optimum fit of the earbuds
The perceived sound quality including bass performance and the
best possible noise cancellation of the earphones depends to a large
extent on the correct fit of the earbuds in the ear.
▷ Pull the ear adapter away from the in-ear sound tunnel.
▷ Mount the new ear adapter to the in-ear sound tunnel. Ensure that
it locks into place.
▷ Test which ear adapter size gives you the best sound quality and
the best wearing comfort.
You can choose between 4 different ear adapters in size XS, S, M
and L. The ear adapters must fit snugly in the ear canal and com-
pletely seal your ears.
Inserting the earbuds into the ears
▷ Assign the right earphone to your right ear and the left earphone
to your left ear.
▷ Insert the earbuds at a slight angle into the ears and twist them
slightly into the ear canal so that they sit comfortably and snugly
in the ear canal (> 20).
LMSXS
Click
You can use the right earbud alone without using the left ear-
bud. The left earbud, however, cannot be used alone.
RightLeft
R
L
1
Using the earphones
CX 400BT True Wireless | 21
Switching the earphones on
▷ Take both earbuds out of the charging case and insert them into
your ears (> 20).
If a paired Bluetooth device is within the transmission range, you
hear the voice prompts “Power On” and “Connected”. The LEDs
of the earbuds light up blue.
Switching the earphones off
The earbuds do not have to be switched off explicitly.
WARNING
Danger of hearing damage due to high volume levels!
Listening at high volume levels can lead to permanent
hearing defects.
▷ Before putting the headphones on, adjust the volume
to a low level (> 22).
▷ Do not continuously expose yourself to high volume
levels.
If you take the earbuds out of the charging case during an
incoming call, the call is automatically accepted and you can
use the earbuds directly for making calls.
This Auto Call function can also be deactivated (> 25).
The earbuds automatically switch to idle mode if no paired
Bluetooth device can be found within 15 minutes. You can wake
up the earbuds from idle mode by touching their touch control
panels 1x or by briefly inserting them into the charging case.
“Power On“
“Connected“
L
LR
Using the earphones
22 | CX 400BT True Wireless
▷ Insert the earbuds into the charging case to switch them off.
As soon as the earbuds are inserted into the charging case, they
switch off and are being charged (> 14).
Adjusting the volume
To increase the volume:
▷ Touch and hold the touch control panel of the right earbud until
the volume is increased.
To reduce the volume:
▷ Touch and hold the touch control panel of the left earbud until the
volume is reduced.
When the minimum or maximum volume is reached, you hear the
voice prompt “Volume max” or “Volume min”.
You can also switch off the earbuds manually (idle mode) via
the Smart Control app.
The earbuds automatically switch to idle mode if no paired
Bluetooth device can be found within 15 minutes. You can wake
up the earbuds from idle mode by touching their touch control
panels 1x or by briefly inserting them into the charging case.
WARNING
Danger of hearing damage due to high volume levels!
Listening at high volume levels can lead to permanent
hearing defects.
▷ Before putting the headphones on and before toggling
between audio sources, adjust the volume to a low
level.
▷ Do not continuously expose yourself to high volume
levels.
You can also adjust the volume using the connected Bluetooth
device.
R
L
Hold Hold
Using the earphones
CX 400BT True Wireless | 23
Using the voice assistant/voice dialing
▷ Tap the touch control panel of the right earbud 1x.
The available voice assistant of your smartphone is activated
(*depending on the system or app on your smartphone: Siri, Goo-
gle Assistant, ...).
▷ Ask the voice assistant your question or make a request.
To cancel the voice assistant/voice dialing:
▷ Tap the touch control panel of the right or left earbud 1x.
Controlling music playback
The music playback functions are only available when the earphones
and the device are connected via Bluetooth. Some smartphones or
music players may not support all functions.
Playing/pausing music
▷ Tap the touch control panel of the left earbud 1x.
Playing the previous track
▷ Tap the touch control panel of the left earbud 2x.
R
ON/OFF
Siri, Google Assistant ...*
1 x
The Smart Control app allows you to customize the control
functions for music playback (> 27).
Left touch control panel Function
Tap 1x Plays or pauses music
R
L
Using the earphones
24 | CX 400BT True Wireless
Playing the next track
▷ Tap the touch control panel of the right earbud 2x.
Making calls using the earphones
The call functions are only available when the earphones and the
smartphone are connected via Bluetooth.
Some smartphones and telephony apps (e.g. WhatsApp, Skype,
WeChat) may not support all call control functions.
During a call, you can use the right and/or left earbud to control the
call functions.
Making a call
▷ Dial the desired number on your smartphone.
If your smartphone does not automatically transfer the call to the
headphones, select “CX 400BT TW” as the audio source on your
smartphone (see the instruction manual of your smartphone if
necessary).
Accepting/rejecting/ending a call
If your headphones are connected to a smartphone and you receive
a call, you hear a ring tone in the headphones.
If you are playing music when you receive a call, the music pauses
until you end the call.
Left touch control panel Function
Tap 2x Plays the previous track in the playlist
Right touch control panel Function
Tap 2x Plays the next track in the playlist
R
L
Using the earphones
CX 400BT True Wireless | 25
Using the Auto Call function
If you take the paired earbuds out of the charging case during an
incoming call, the call is automatically accepted and you can use the
earbuds directly for making calls.
You can activate (default setting) or deactivate the function via the
Smart Control app.
Displaying the battery charge status
When the earphones are connected to your Bluetooth device, the
battery charge status can be displayed on the screen of your smart-
phone or device (depending on the device and operating system
used).
The Smart Control app also displays the charge status of the ear-
buds' rechargeable batteries.
Displaying the battery charge status using the charging case
If no USB cable is connected to the charging case:
▷ Press the LED button of the charging case.
The LED of the charging case displays the battery charge status
for 5 seconds:
Right or left touch control
panel
Function
Tap 1x
Accepts a call
Tap 1x
Ends a call
Voice prompt “Call ended”
Tap 2x
Rejects a call
Voice prompt “Call rejected”
Tap 1x
Accepts an incoming call and ends
the active call
Tap 2x
Rejects an incoming call and contin-
ues the active call
You can use the right earbud alone without using the left ear-
bud. The left earbud, however, cannot be used alone.
1x 1x
Using the earphones
26 | CX 400BT True Wireless
LED
Charging case WITH
earbuds inserted
Charging case
WITHOUT earbuds
inserted
lights up
green
... earbuds are fully
charged and the
charging case can
still charge at least
one complete cycle
... charging case is
fully charged
pulses
yellow
... earbuds are being
charged via the
rechargeable bat-
tery of the charging
case
–
lights up
yellow
... earbuds are fully
charged, the
charging case
cannot charge
another complete
cycle
... charging case is
charged less than
90 %
lights up
red
... rechargeable bat-
teries of the earbuds
and the charging
case are empty
... rechargeable bat-
tery of the charging
case is empty
flashes
red
... a charging error/
battery error has
been detected in at
least one earbud (>
30)
... a charging error/
battery error has
been detected in the
charging case (> 30)
Using the earphones
CX 400BT True Wireless | 27
Adjusting sound effects/the equalizer
To be able to use the sound effects/equalizer, you require the Smart
Control app (> 19).
▷ In the Smart Control app, select the desired sound effects via the
equalizer. You can use predefined presets or define your own set-
tings.
The sound effects are stored in the earphones. These sound set-
tings are active even without using the Smart Control app, i.e.
when you are using a different Bluetooth device.
Setting the voice prompts/beep sounds
To be able to set the voice prompts and beep sounds, you require the
Smart Control app (> 19).
You can change the language of the voice prompts, choose between
voice prompts and beep sounds, or deactivate the status messages
with a few exceptions (e.g. rechargeable battery is empty).
Customizing the control functions
To be able to customize the control functions for music playback, you
require the Smart Control app (> 19).
The app allows you to customize the control functions and other
commands or to select preset control functions. Some basic func-
tions cannot be changed (e.g. volume loud/quiet, call control).
Using the earphones
28 | CX 400BT True Wireless
Storing or transporting the earphones in
the charging case
Store the earphones in the charging case to prevent damage to the
earphones when you are not using or transporting them. The ear-
phones are automatically charged in the charging case so you
always have the full battery life to work with.
▷ Open the charging case by overcoming a slight magnetic resis-
tance and insert the left earbud into the left charging compart-
ment and the right earbud into the right charging compartment.
The earbuds are magnetically pulled into the charging compart-
ments.
▷ Close the charging case.
LR
Care and maintenance of the earbuds/charging case
CX 400BT True Wireless | 29
Care and maintenance of the
earbuds/charging case
▷ 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.
CAUTION
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.
L
Click
LMSXS
Care and maintenance of the earbuds/charging case
30 | CX 400BT True Wireless
Information on the built-in rechargeable
battery
Sennheiser ensures and guarantees that the rechargeable battery
performs at its optimum upon purchase of the product. If, upon pur-
chase or within the warranty period, you suspect that the recharge-
able battery is obviously defective or if a charging error/battery error
is displayed (> 7), stop using the product, disconnect it from the
power supply system and contact your Sennheiser partner. Your
Sennheiser partner will coordinate the repair/replacement with you.
Do not return a product with a defective battery to your dealer or
Sennheiser partner unless requested to do so. To find a Sennheiser
partner in your country, search at www.sennheiser.com/service-
support.
Installing firmware updates
Firmware updates can be downloaded free of charge from the Inter-
net using the Sennheiser Smart Control app.
▷ Connect your earphones to your smartphone and start the Smart
Control app (> 19).
▷ The app provides information on available firmware updates and
guides you through the installation process.
FAQ/If a problem occurs ...
CX 400BT True Wireless | 31
FAQ/If a problem occurs ...
Current list of frequently asked questions (FAQ)
Visit the CX 400BT True Wireless product page at
www.sennheiser.com
There you will find a current list of frequently asked questions (FAQ)
and suggested solutions.
Your question has not been answered or the problem persists?
If a problem occurs that is not listed in the FAQ section or if the prob-
lem cannot be solved with the proposed solutions, please contact
your Sennheiser partner for assistance.
To find a Sennheiser partner in your country, search at
www.sennheiser.com > “Service & Support”.
Leaving the Bluetooth transmission range
Wireless calling and streaming are only possible in the Bluetooth
transmission range of your smartphone. The transmission range
largely depends on environmental conditions such as wall thickness,
wall composition etc. With a free line of sight, the transmission
range of most smartphones and Bluetooth devices is up to 10 meters.
If you, and therefore the earphones, leave the Bluetooth transmission
range of the smartphone, the sound quality deteriorates increasingly
until you hear the voice prompt “No connection” and the connection
breaks down completely. If you immediately re-enter the Bluetooth
transmission range, the connection is automatically re-established
and you hear the voice prompt “Connected”. If this is not the case,
tap the touch control panel of the earbud 1x.
The right earbud (primary earbud) can be used alone. The left earbud
(secondary earbud) cannot be used alone because it requires the
right earbud for Bluetooth transmission.
Resetting the earphones
If the function of the earphones is disturbed, perform a reset. Individ-
ual settings such as the pairing settings are not deleted.
▷ 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 (>
29).
▷ Use the USB cable to connect the charging case to a power
source (> 14).
▷ Insert the earbuds into the charging case and touch and hold the
right and the left touch control panel for 5 seconds.
The reset of the earphones is completed.
FAQ/If a problem occurs ...
32 | CX 400BT True Wireless
Resetting the earphones to the factory default settings
If the function of the earphones is disturbed and a reset (> 31) does
not improve, reset the earphones to the factory default settings. This
deletes, among other things, all pairing settings.
The Smart Control App allows you to reset the earphones to the fac-
tory default settings via the settings menu.
LR
5s
Specifications
CX 400BT True Wireless | 33
Specifications
CX 400BT True Wireless
Model: CX400TW1, CX400TW1 C, CX400TW1 L, CX400TW1 R
Bluetooth
Wearing style true wireless stereo earphones
Ear coupling ear-canal, closed-back
Frequency response 5 Hz to 21 kHz
Transducer principle dynamic
Transducer size 7 mm
Sound pressure level (SPL) 114 dB (1 kHz/0 dBFS)
THD (1 kHz, 94 dB SPL) < 0.08 %
Microphone principle MEMS
Microphone frequency
response
100 Hz to 10 kHz
Microphone pick-up pattern
(speech)
2-mic beamforming array
Power supply built-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 time 7 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 batteries
approx. 1.5 hrs
Temperature range operation: 0 to +40°C
storage: –25 to +70°C
Relative humidity operation: 10 to 80%, non condensing
storage: 10 to 90%
Magnetic field strength earbuds: 0.63 mT
charging case: 101 mT
Weight earbuds: approx. 6 g each
charging case: approx. 37 g
Version Bluetooth 5.1 compatible, class 1, BLE
Transmission frequency 2,402 MHz to 2,480 MHz
Modulation GFSK, π/4 DQPSK, 8DPSK
Profiles HSP, HFP, AVRCP, A2DP
Output power 10 mW (max)
Codec aptX®, AAC, SBC
Specifications
34 | CX 400BT True Wireless
Device name CX 400BT TW
LE-CX 400BT TW (Bluetooth Low
Energy only)
Number of active
connections
1
Manufacturer Declarations
CX 400BT True Wireless | 35
Manufacturer Declarations
Warranty
Sennheiser electronic GmbH & Co. KG gives a warranty of 24 months
on this product.
For the current warranty conditions, please visit our website at
www.sennheiser.com 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 spe-
cific requirements
EU declaration of conformity
• RoHS Directive (2011/65/EU)
Hereby, Sennheiser electronic GmbH & Co. KG declares that the
radio equipment type CX400TW1 (CX400TW1 R, CX400TW1 L,
CX400TW1 C) is in compliance with the Radio Equipment Directive
(2014/53/EU).
The full text of the EU declaration of conformity is available at the fol-
lowing Internet address: www.sennheiser.com/download.
Notes on disposal
• Battery Directive (2006/66/EC & 2013/56/EU)
• WEEE Directive (2012/19/EU)
The symbol of the crossed-out wheeled bin on the product, the bat-
tery/rechargeable battery (if applicable) and/or the packaging indi-
cates that these products must not be disposed of with normal
household waste, but must be disposed of separately at the end of
their operational lifetime. For packaging disposal, please observe the
legal regulations on waste segregation applicable in your country.
Further information on the recycling of theses products can be
obtained from your municipal administration, from the municipal col-
lection points, or from your Sennheiser partner.
The separate collection of waste electrical and electronic equip-
ment, batteries/rechargeable batteries (if applicable) and packag-
ings is used to promote the reuse and recycling and to prevent neg-
ative effects caused by e.g. potentially hazardous substances
contained in these products. Herewith you make an important con-
tribution to the protection of the environment and public health.
Trademarks
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 Sennhe-
iser electronic GmbH & Co. KG is under license.
Qualcomm aptX is a product of Qualcomm Technologies Interna-
tional, Ltd. Qualcomm is a trademark of Qualcomm Incorporated,
registered in the United States and other countries, used with per-
mission.
Manufacturer Declarations
36 | CX 400BT True Wireless
aptX is a trademark of Qualcomm Technologies International, Ltd.,
registered in the United States and other countries, used with per-
mission.
Other product and company names mentioned in the user documen-
tation may be the trademarks or registered trademarks of their
respective holders.
