Fosi Audio C4 Soundbar – Review

Fosi Audio C4 Soundbar

Fosi Audio C4 Soundbar

| 2x Dynamic Drivers | 2x Bass Woofers | 2x 5W |

Fosi Audio C4 Soundbar, one of the few current speakers from Fosi Audio.

We have reviewed several products from Fosi Audio and as you might have noticed, the brand is much more popular as an amplifier, DAC, speaker amp manufacturer but they do also offer some speakers and soundbars.

The Fosi Audio C4 is the 4th and latest generation of their computer speakers/soundbars.

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Fosi Audio C4 Soundbar Review

Tests & Scores


Accessories & Packaging

The Fosi Audio C4 comes inside a rectangular box with sufficient padding, that contains inside:

• Speaker
• USB-C cable

gramophone-25660  3/5



The Fosi Audio C4 has an elongated form factor, as you would expect from a speaker labeled as a soundbar.

The shape of the soundbar makes it a perfect companion to be placed and used either under a monitor/TV or to the side of it matching seamlessly with the system.

The speaker has a full black color finish that extends from the main case to the frontal grid but with silver colored buttons/knob.

Behind the grids, the soundbar sports a dual driver configuration and dual bass woofer audio system.

On top of this, the soundbar has two nicely placed LED light strips behind a translucid white cover to diffuse and even up the light coming from the LED strips. These light strips can be seen on the bottom and top of the frontal case and grid.

The strip LED lights offer 5 light modes and most them being dynamic that react lively to the sound/music.

Overall, the lighting of the Fosi Audio C4 add a nice embellishing detail – even more with the music/sound reacting presets.

Moreover, the brand applied a smart design to the case/shell of the soundbar allowing it to be used fully flat sitting on the bottom case or pointing 45 degrees upwards by titling the speaker. When used tilted, the soundbar will sit on some specially designed curves and grooves on the bottom back section of the case that combine with the cable itself to provide a secure and stable titled positioning of the unit.

The specific dimensions of the Fosi Audio C4 Soundbar are:

• Length: 430mm (17 inches)
• Height: 68mm (3 inches)
• Depth: 70mm (3 inches)
• Weight: 760 grams

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gramophone-25660 4.5/5



Construction Quality and Build

The Fosi Audio C4 soundbar is mainly constructed with plastic with the only exceptions being the metal front grid and the knob.

Despite the main plastic construction, the soundbar feels fairly rugged without showing any substantial weak sections.

Buttons, knob and connectors are firmly put together with no traces of wobbliness.

The bottom section of the case is equipped with two silicone strips that are very grippy and do an excellent job keeping the speaker “slide-free”.

gramophone-25660 4/5


Operation & Control

The Fosi Audio C4 soundbar has in total 4 buttons and a knob; the knob controls the power on/off and the volume of the unit while the 4 buttons are used for:

• Play/pause
• Phone calls answer/reject
• Switch input modes
• EQ/sound modes switch

The knob offers a stepless rotation movement and a final click on the clockwise top end that corresponds to the power on/off switch – the knob rotation does not have any clicky nor audible feedback.

Each step on the knob corresponds to 7 steps of volume increment/decrement on Windows 10 while connected through the wireless Bluetooth mode – if you are looking for very fine control of the volume, the 7 steps jump might be too much for you. When used connected and used in USB mode, the soundbar’s knob has a finer control that sometimes can be achieved as 2 steps per rotational step but sometimes it also applied 4 to 6 steps.

Maybe subjectively according to our taste but we found that the rotational movement of the volume knob to be inverted for our logical thinking, being that this soundbar increases the volume by rotating the knob counterclockwise instead of clockwise.

gramophone-25660 3.75/5




The specs of the Fosi Audio C4 can make it compete without shortage against many popular and mainstream Bluetooth speakers thanks to a wide frequency response that covers 70Hz to 20.000Hz and its 2x active full range speakers + 2x woofers.

Even when compared with the good internal PC stereo speakers of our 43″ 4K, the Fosi Audio C4 soundbar offers a remarkable upgrade in sound quality, fullness, bass, punch and clarity – even more respectable considering that the internal speakers in our compared monitor are larger than the speakers inside the Fosi Audio soundbar and also have double the rated power.

Talking about power, the Fosi Audio C4 soundbar provides a huge volume output for a desktop soundbar that is being powered simply by a common USB port of your PC.

The C4 includes 2 EQ/Sound-Modes, one intended for music listening and other for gaming. Sound-wise, the 2 EQ/modes are drastically different, having a more directional but clearer vocals and full sound in music mode and a substantially spatially-wider one in gaming mode. Fosi Audio lists as a bass-boosting mode for the gaming mode but we found it to be more of a bass-focused, mids/highs smoothed and spreading sound than providing a stronger bass boost.

The Fosi Audio C4 is born as a soundbar but it also offers a headphone out connection, making it a headphone amp as well, yet throughout our tests we noticed that this was the weakest feature of the soundbar as the sound quality from this headphone jack was substantially inferior and bass-lacking than to the level provided through the speakers themselves – to be honest, we consider the headphone connection as a sort of “freebie” feature and not a main fundamental one.

With its internal DSP chip and multi-driver configuration with dedicated bass woofers you can actually feel the physical bass rumble coming from the speakers and being transmitted to the desk.

gramophone-25660 4/5



Offering 3 of the most common types of audio connections (Bluetooth, USB audio and 3.5mm stereo), the Fosi Audio C4 Soundbar is a breeze to connect with many devices either wired or wirelessly. You might see from Fosi Audio itself naming the USB connection as a power-only connection but it is actually both used for power and for USB-audio.

The 3.5mm stereo jack should not be confused with an input stereo jack as this is, instead, a 3.5mm for headphone output sound. This means that the connector is used to plug your headphones to the soundbar and use the C4 as your headphone amp.

The USB connection works also as the power input of the soundbar as the speaker is fully powered by an USB connection – as long as the USB port or USB PSU is able to provide 5V 1A.

gramophone-25660 4.25/5


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Fosi Audio C4 Soundbar Technical Specifications



Dual Driver

Driver Unit

2x5W + 2x woofers



Max Power

2x5 W





Frequency response







USB Type-C


Approx. 768g

Supplied Accessories


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Scores Scores

Fosi Audio C4 Soundbar Scores

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Fosi Audio C4 Soundbar