Thank you very much for purchasing the C4 Computer Soundbar.

Please read the instructions carefully before using this product.

Packing list
Button Function
Quick Setup
LED Light Mode
Troubleshooting/ QA
About Fosi Audio


Thank you very much for purchasing the C4 Computer Soundbar.

Please read the instructions carefully before using this product.

If you have any problems or suggestions for the product, please contact us via support@fosiaudio.com.


Product name   

Computer soundbar 


Output power    




5V/ 2A 


Speaker frequency

70Hz- 20KHz 


Bluetooth version



Bluetooth range

Up to 10m 


I Dimensions

430mmx 70mm X 68mm

Packing list

Button Function

① Power/Volume Knob: counterclockwise to turn on and raise the volume, clockwise to lower the volume and turn off.

② Mic: phone call.

③ M: Switch input mode. Clear the paired devices on the C4 soundbar.

④ Change Lighting Mode: Press the one.

⑤ EQ: Press the one to switch music or bass mode.


① Aux 3.5mm Line In

② Type-C Charging Port

③ 3.5mm Headphone Output

Quick Setup​

Wireless Connection Via 


① The default input setting is Bluetooth mode after booting the soundbar.

② The Bluetooth mode is on when the light flashes blue.  

NOTE: How to switch to wired mode from Bluetooth mode?

Click the power button and you will hear a tone meaning the bluetooth mode is off.


Wired Connection with 3.5mm 


① Insert the USB Plug into a USB port of a desktop, laptop, tablet,  power bank, etc .

② Insert the 3.5mm Audio plug into 3.5mm jack of your device.

NOTE: Make sure the soundbar is not in Bluetooth mode .

Extra driver or software installation is not needed, just plug and play .


LED Light Mode

Touch LED Light : 

With a light touch, the backlit mode of the RGB lighting bar can be switched with 5 modes .

Change lighting modes:

Press the ‘ Fosi ’ button ones .

Press and hold for 2 seconds to turn off LED lighting .



Q1. Pairing connection via Bluetooth cannot be completed.

Once you connect a device to the soundbar, the connection will be stored. When you turn on the soundbar, the Bluetooth connection will be activated automatically. To connect another device to the soundbar, you need to disconnect the former connection first: turning off Bluetooth on your former device, or clearing the former connection by pressing and holding the Power button for 3 seconds. After that, you can find and connect the other devices.

Q2. The Bluetooth connection is not stable.

There should be some obstructions between the soundbar and your Bluetooth devices which interfere with the connection. Please remove them. The supported range for the Bluetooth connection is around 10 meters indoor. Please do not exceed that range.

Q3. Silent play after connection via Bluetooth.

After connections with mobile devices, Bluetooth device audio is off. Turn on the mobile’s output volume.

Q4. No sound after connection via Bluetooth.

① Configure the sound output device on your device (System>Sound>Output>Choose your output device).

② Turn up the volume on your soundbar, device, or application.


About Fosi Audio


Fosi Audio designs and builds innovative audio products with all your music in mind. Great sound, simple but elegant designs, high-quality materials, and truly useful features are what Fosi Audio is about. We sincerely hope you get as much enjoyment from our products as we’ve had to create them!

Our website: www.fosiaudio.com

Amazon store: www.amazon.com/fosiaudio

Our Youtube channel: Fosi Audio

Our Facebook page: Fosi Audio

After-sale Service and Technical Support Email:  support@fosiaudio.com