PC Components

Cool Master MasterBox MB400L – Spacious mini-tower supports optical drive

The hardware manufacturer Cooler Master is adding another product to its MasterBox series of cases. This is the Cooler MasterBox MB400L. The MB400L is based on the popular body of the NR400, but instead of mesh, it has a plastic front in aluminium look. In addition to the visual appearance, this tower should also convince with a lot of space, a versatile airflow concept and with the slot for an external 5.25″ drive. The MB400L is offered in four different versions: with/ without ODD bay, with/ without tempered glass. However, the two variants with tempered glass will not be released for the German market.

Cooler Master for the version with ODD bay is estimated at about 60 Euro (current: € 73.78 *). Whether the Cooler MasterBox MB400L still keeps up with the competition at this price and how it performs in general, you can read in this review.

Technical details

Model: Cooler Master Masterbox MB400L
Case type: Mini-Tower
Dimensions: 218 mm (W) x 410 mm (H) x 411 mm (D)
Weight: approx. 5.47 kg
Material: Steel, plastic
Color: black
Front connectors: 1x USB 3.0 Type-A, 1x USB 2.0 Type-A, 1x Audio Combo Port (Audio+Mic)
Drive bays: 1x 5.25″ (internal)
2x 3,5″ (internal)
2x 2,5″ (internal)
Expansion slots: 4x horizontal
Form factors: mATX, mini-ITX
Ventilation: front: 2x 120 mm or 2x 140 mm
Back side: 1x 120 mm
Cover: 1x 120 or 1x 140 mm
Radiators: front: 1x 240 mm or 1x 280 mm (without ODD cage)
Rear: 1x 120 mm
Max. CPU cooler height: 166 mm
Max. graphic card length: 344 mm
Max. max. length of power supply: up to 325 mm (without HDD cage), 140 (with HDD cage)
Place for cable management: up to 18-22 mm
Price: € 73.78 *
Specials: dust filter, cable management, external ODD shaft

Scope of delivery

The Cooler Master MB400L comes well and safely packed in a brown cardboard box with black writing. Inside the box the tower is wrapped by two blocks of normal styrofoam and a plastic foil. On the box are pictures of the tower and all important technical data printed. The included accessories are in a bag and are fixed inside the case with a cable tie. Included are all important screws, an instruction manual, nine black cable ties, a nut for screwing in spacers and four rails for mounting hard disks. Also included are the pre-installed 120 millimetre fan, pre-installed spacers and a magnetic dust filter for the lid.

Outside impression

The Cooler MasterBox MB400L has an extremely discreet and timeless design. Although the front panel is made of plastic, it looks like brushed aluminium. In the upper area there is a removable panel for the 5.25″ drive. As with every manufacturer, the logo is of course also included. But in order to keep the simple look of the front, Cooler Master deliberately does without the logo. The logo is framed by a strip of clear plastic. This allows an RGB fan mounted behind the front to shine through easily. In order to be able to guarantee a good airflow, the front panel has large mesh elements on both sides, which also serve as dust filters. Moreover, two fans (120 or 140 millimeters) can be mounted in the front.

The cover of the MB400L is characterized above all by a large opening for fans or radiators. The opening is slightly recessed and does not sit symmetrically in the lid. To improve the appearance and to protect against dust, Cooler Master adds a magnetic dust filter to this mini tower. The manufacturer has also placed the I/O panel in the lid. This has two USB ports (1x USB 3.0, 1x USB 2.0), a combo port for headphones and microphone, and two buttons for power and reset.

The unobtrusive design also continues on the side. The MB400L has two normal steel side panels. These have “captive thumbscrews” and recessed grips to make dismantling easier. The stability of the side panels is just about right for the price range targeted. It is also noticeable that the left side panel does not cover the entire side. The lower quarter belongs to the body or the power supply cover and is firmly riveted.

The back and underside of the tower reveal no special features. The case stands on four short plastic feet, which are equipped with thin rubber buffers to minimize noise. To protect it from dust, unfortunately only a simple mesh filter mat was attached to the bottom. Above the power supply, the MB400L has four slots for expansion cards. These have to be broken out and there are no spare covers included. Finally, only the pre-installed case fan is to be mentioned on the back. The mounting is done with four screws and is variable by a rail system.

Internal impression

Inside, Cooler Master uses a proven concept in the form of a two-chamber system with plenty of space for hardware and radiators. The large main chamber offers space for a mainboard in mATX format and expansion cards. The mainboard tray is completely closed, except for a cutout for CPU cooler backplates and several cable management openings. This makes the tower torsionally stiff even without side panels.

Since there are no HDD slides in the front, optional front fans can supply the interior of the Mini Tower with fresh air without hindrance. The heated air is discharged via the pre-installed fan at the rear. Additional fans can be installed in the lid. Due to the staggered mounting rails, a radiator could perhaps also find room here, but high RAM or VRM coolers could quickly put a stop to this.

As usual, the separation of the large and small area is done by a power supply cover. This cover is mainly closed and also represents a part of the left outer cover. The main purpose of the cover is to achieve a better look, as unnecessary cables and the hard disk cage are covered. Finally, the cover also has two cable management openings and two mounting points for SSDs.

Since there is nothing more to say about the front, we now turn to the back. Here you’ll find various mounting points for cable ties and two potential mounting points for 2.5″ SSD frames. The buyer has up to 22 millimeters of space available here for laying the cables. In the area below the cover, the power supply finds room on four narrow rubber buffers. In addition, the manufacturer has attached the modular hard disk cage.

As a last point in this chapter we would like to talk about the possibilities for installing data carriers. In total, seven data carriers could be installed in the Cooler Master MB400L. However, a maximum of four data carriers are supported ex works or with the supplied accessories. Up to three 3.5″ hard disks find space in the HDD cage underneath the power supply cover. The mounting is done via two mounting rails which are simply plugged in. Cooler Master has come up with an interesting solution for mounting SSDs. Four decoupling rings can be plugged into the corps at each of four possible locations. After the SSD has been fitted with narrow pins, the data carrier can then simply be plugged into the desired location.

System building in the Cooler Master MB400L

Now we come to the system installation. As hardware we use a AMD Ryzen 5 1600 on a Gigabyte B450 I Aorus Pro WIFI* with 32GB Crucial Ballistix Sport LT grey DDR4-3000. The Ryzen is cooled by an EKL Alpenföhn Matterhorn Pure. For the image output a GTX 1060 6GB from Gigabyte AORUS is responsible. The power supply does the non-modular Berlin Pro RGB 650W with RGB fan.

The installation of the system was done quickly and there were no significant complications. The space is adequate for a mini tower and the spacers are pre-installed for a normal mATX mainboard. The six cable management openings are sensibly placed and the space behind the mainboard tray is quite ample with a maximum of 22 millimeters. All this has contributed to the fact that we were able to conjure up a tidy system in the Cooler Master MB400L.

As far as the general hardware compatibility is concerned, buyers hardly need to worry about it. Graphics cards are supported up to a maximum length of 344 millimeters and CPU coolers up to a maximum height of 166 millimeters. This is sufficient for all current GPUs and for very many CPU coolers. Despite the compact design, the power supply unit can also be up to 325 millimetres long. In this case, however, the buyer must do without the HDD cage and a front radiator. With HDD cage, the power supply shouldn’t be longer than 140 millimeters. This already limits the failure noticeably. The compatibility with water cooling is also limited. A maximum of a 280 millimeter radiator is supported in the front and without an optical drive.

Cooler Master equips the MB400L with a simply designed fan ex factory. Power is supplied via a normal 3-pin connector, whose cable is also black. The maximum speed of the fan is 1300 revolutions per minute. At full speed, the fan can be clearly heard from the system.

Finally, we come to the temperatures reached in the Cooler Master MB400L. During the load test, Prime95 and FurMark were run for 15 minutes at a room temperature of 27 °C. Additionally, this test was carried out in four different variants (case fan to 12V, case fan to 7V, two additional front fans, without front panel). In all scenarios, the Ryzen 5 1600 was overclocked to 3.6 GHz and supplied with a voltage of 1.225V.

CPU: 50% PWM (1100 rpm)
GPU: 50% PWM (1650 rpm)
Case: 12V (1300 rpm)
CPU: 78 °C
GPU: 82 °C
CPU: 50% (1100 rpm)
GPU: 50% PWM (1650 rpm)
Case: 7V (830 rpm)
CPU: 85 °C
GPU: 82 °C
CPU: 50% (1100 rpm)
GPU: 50% PWM (1650 rpm)
Case: 7V (700 rpm) + 2 additional front fans
CPU: 75 °C
GPU: 72 °C
CPU: 50% (1100 rpm)
GPU: 50% PWM (1650 rpm)
Case: 7V (700 rpm) + 2 additional front fans
without front panel
CPU: 69 °C
GPU: 69 °C

If you run the Cooler Master MB400L in the standard configuration and throttle the fan a bit, the test system doesn’t exactly stay cool. Already two additional front fans can reduce the temperatures of processor and graphic card by ten degrees. If you want to install gaming hardware in the MB400L and not just an office system, additional front fans are clearly mandatory.

Conclusion on the Cooler Master MB400L

Now we have reached the end again. With the MB400L, Cooler Master has brought an interesting and well equipped case to the market. The mini-tower offers a lot of space for hardware, has a rock-solid finish and, depending on the variant, even has room for an optical drive.

Basically the MB400L is also available with a side window made of tempered glass. However, these versions are not available in Germany and are not planned for the German market. In our opinion, there is no conclusive reason for this. We also noticed a negative aspect of the cooling capacity which this mini tower offers ex works. Gaming hardware will probably quickly reach its temperature limits without additional fans. Moreover, Cooler Master does without a second USB 3.0 port in the I/O panel in the variant with ODD slot and relies on non-reusable PCI slot bezels.

As always, the price also plays an important role. The Cooler Masterbox MB400L costs about 60 Euro in the version with ODD slot (current: € 73.78 ). Thus it is in the same price range as the NR400 from our own company. But the NR400 not only offers better airflow, it also comes with tempered glass, another fan and rubberised cable management openings. In order to keep up with the competition, the MB400L has to become slightly cheaper in both versions.

Cooler Master MasterBox MB400L

Value for money


Spacious mini-tower with a simple look and support for optical drives, but at a slightly too high price.

Simon Lüthje

I am co-founder of this blog and am very interested in everything that has to do with technology, but I also like to play games. I was born in Hamburg, but now I live in Bad Segeberg.

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