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NZXT Kraken X31 & X41 Liquid CPU Coolers

NZXT Kraken X31 & X41 Liquid CPU Coolers

August 11, 2014 by Lawrence Lee

Product
NZXT Kraken X31 Liquid CPU Cooler NZXT Kraken X41 Liquid CPU Cooler
Manufacturer
NZXT NZXT
Street Price
US$75 US$100

While all-in-one liquid CPU coolers are marketed as high-end solutions to enthusiasts, our previous encounters with them have left us wanting. A closed loop system with fluid continually being cycled between a small reservoir sitting atop the processor and a large heat exchanger mounted to an exhaust fan position is a cool idea, but they've always failed to impress on our heatsink test platform. Usually they deliver lackluster cooling performance at higher noise levels than regular heatsinks due to the presence of the pump, and on top of that, they carry a price premium. There also hasn't been much innovation as their basic design has hardly changed since their inception. Pluck a random all-in-one liquid CPU cooler off a manufacturer's catalog and hide the labels, and you'd be hard pressed to identify it correctly. Yet, all-in-one water coolers appear to have become ubiquitous; there's hardly a "serious" case without mounts and accommodations for water cooling radiators any more. The attraction for the overclocker may be the higher maximum clocks that can be achieved relatively simply, without much attention to overall case cooling or high noise levels.



The NZXT Kraken X31 & X41 boxes.

We'd be really excited if NZXT broke the mold with the Kraken X31 and X41, but as you can see from the illustrations on the packaging, they look more or less the same as others that have preceded it. It has the familiar round base and dense radiator design found in countless other models, including the first such cooler we reviewed four years ago, the Corsair Hydro H50. The two Krakens are identical except for the size of the radiator and fan. The X31 is the smaller of the two, with its radiator fitting snugly into 120 mm fan mount, while the X41 is thicker and requires a 140 mm placement. NZXT's marketing for the two coolers touts their various advantages: A variable speed pump, extra long tubing for better compatibility with big cases, desktop software for monitoring/controlling fan speeds and an upcoming mobile app counterpart for off-site management, and a six year warranty. The X41 also has a bonus feature in that the top of the waterblock lights up in a variety of colors.



X31 packaging.



X31 package contents.

The coolers are packed the same way with the same accessories. The cooler is housed, coiled up like a snake, in a paper carton, with the radiator and fan protected further by cardboard cutouts. The base has a layer of thick thermal compound pre-applied and a protective plastic shell. Also included is a succinct assembly guide with diagrams but devoid of words, a single fan (120 mm for the X31, 140 mm for the X41), an Intel backplate (the stock backplate is used for AMD installs), an AMD mounting frame (the Intel mounting frame is installed out-of-the-box), and the various screws, bolts, standoffs, and nuts used to put it all together.

NZXT Kraken X31/X41: Specifications

(from the product
web pages located here and here)
Model Number RL-KRX31-01 RL-KRX41-01
Compatibility Intel LGA 2011-3, 1366, 1156, 1155, 1150 CPUs

AMD FM2, FM1, AM3+, AM3, AM2+, AM2 CPUs
Material Copper, Aluminum, Rubber, Plastic
Radiator Dimensions 155 x 120 x 30mm 140 x 172.5 x 36mm
Tube Length 400mm
Motor Speed 2400-3600 ± 150 RPM
Motor Current 325mA
Motor Voltage 12V DC
Motor Connector 3-Pin
Fan Dimensions 120 x 120 x 25mm 140 x 140 x 25mm
Fan Speed 800-2000 RPM ± 10%
Fan Air Flow 81.32 CFM (max.) 42.4-106.1 CFM
Fan Air Pressure 0.44 - 2.76 mmH20 0.36-1.97mmH2O
Fan Noise Level 18-34 dBA 20-37 dBA
Fan Bearing Hydro Dynamic Bearing Nano Bearing
Fan Voltage 12V DC
Fan Connector 4-Pin PWM
Control Method Kraken+ Software Module
Warranty 6 Years

PHYSICAL DETAILS

The Kraken X31 and X41 are constructed in typical fashion. A round copper base pulls heat off the CPU heatspreader, passing it on to the liquid in a small reservoir and pump integral to the base. The coolant is pumped through 40 cm of 1.0 cm diameter tubing to a radiator with thin aluminum coils arranged in rows and an exhaust fan. The fluid then travels back to the base to the complete the cycle. According to our measurements, the base of both coolers has a diameter of 6.4 cm and a height of 3.1 cm, while the radiators measure 15.6 x 11.9 x 3.0 cm and 17.5 x 14.0 x 3.5 cm for the X31 and X41 respectively.



The X41 radiator doesn't appear that much larger, being both longer and wider by only about 2 cm. However, when you account for thickness as well, the difference in volume is more than 50%. It should also be noted that a 140 mm fan placement with 140 mm mounting holes is required for the X41, something not found in most cases.



The heat dissipation area is vast as the radiator's coils are just 0.15 mm thick with approximately 1.07 mm of separation.



One advantage of these coolers is the modest waterblock height that fits easily in virtually any case. There are three different cables coming out of the housing: a 20 cm 3-pin connector for the pump, a 25 cm dual-headed 4-pin connector for one or two fans, and a 50 cm USB cable that is required for NZXT's software.



A thin, round, copper base with a diameter of 54 mm facilitates heat exchange with the CPU. The plastic housing surrounding it extends a further 10 mm outward. The Intel mounting frame is installed by default on top of the structure.



The base is not as finely finished as most air-cooled heatsinks, with coarse circular machine marks visible throughout. The surface shape is similar to that of Scythe Kotetsu and Ashura, convex with a pin-sized summit at the center.

INSTALLATION

The most critical aspect of installation is that the cooler
be securely mounted as a firm mating results in good contact between the
base and the CPU heatspreader, generating more efficient heat conduction. Ideally it
should also be a simple procedure with the user having to handle as few pieces
of hardware as possible. NZXT's system isn't particularly sophisticated, but as it doesn't need to support that much weight, the simple design is reasonably effective while being a snap to put together.



A plastic backplate is held in place by double-sided standoffs and the base is secured to it using thumbnuts. Long bolts and washers are used to attach fans to the radiator, and short screws secure it to a fan placement inside the case.



The X41 features lighting on the waterblock cap with several different color options adjustable via software.



We've moved our CPU testing system to the Puget Systems Test Bench as it allows us to place the X31's radiator securely in the same position it would occupy in a case. The larger X41 requires 140 mm mounting holes so it was set atop an appropriately sized box along the top edge of the motherboard, simulating a case ceiling installation.



The heat exchanger is bolted to the exhaust fan position though the stock screws didn't work in our case, as the bench's acrylic is much thicker than the back of a typical steel case.



After testing, we found the thermal compound imprint to be uneven but appropriately snug at the center, where it counts most. The faint residue indicates good contact being made with the CPU heatspreader.

TESTING

Before thermal testing, we took some basic physical measurements of the radiator for comparison.

Large Heatsink Comparison:

Average Fin Thickness & Spacing
Heatsink
Fin Thickness
Fin Spacing
SilverStone Heligon HE02
0.52 mm
3.30 mm
Thermalright HR-01 Plus
0.45 mm
3.15 mm
Thermalright HR-02 Macho
0.34 mm
3.12 mm
Thermalright HR-22
0.53 mm
2.74 mm
Scythe Ninja 3
0.39 mm
2.64 mm
Noctua NH-U12P
0.44 mm
2.63 mm
Noctua NH-C12P
0.47 mm
2.54 mm
Noctua NH-D14
0.43 mm
2.33 mm
Thermalright Archon SB-E
0.49 mm
2.33 mm
GELID Tranquillo Rev.2
0.40 mm
2.30 mm
Phanteks PH-TC12DX
0.39 mm
2.30 mm
GELID GX-7 Rev.2
0.31 mm
2.25 mm
Phanteks PH-TC14PE
0.40 mm
2.21 mm
be quiet! Dark Rock 2
0.38 mm
2.22 mm
Prolimatech Armageddon
0.51 mm
2.08 mm
Prolimatech Megahalems
0.50 mm
2.00 mm
Zalman CNPS10X Quiet
0.40 mm
2.00 mm
Scythe Ashura
0.43 mm
1.97 mm
Scythe Kabuto & Zipang 2
0.34 mm
1.94 mm
NZXT Havik 140
0.41 mm
1.91 mm
Scythe Mugen-2
0.31 mm
1.89 mm
SilverStone Tundra TD03 (radiator)
0.43 mm
1.86 mm
Swiftech Polaris 120
0.43 mm
1.85 mm
SilverStone Argon AR01
0.30 mm
1.85 mm
Thermalright Venomous X
0.53 mm
1.84 mm
Scythe Mugen 4
0.30 mm
1.82 mm
Noctua NH-D15
0.46 mm
1.79 mm
Noctua NH-C14
0.38 mm
1.79 mm
Enermax ETS-T40
0.40 mm
1.79 mm
Scythe Yasya
0.32 mm
1.78 mm
be quiet! Shadow Rock Slim
0.42 mm
1.73 mm
SilverStone Argon AR03
0.42 mm
1.72 mm
Noctua NH-U14S
0.42 mm
1.72 mm
Cogage TRUE Spirit 1366
0.40 mm
1.70 mm
Arctic Cooling Freezer Xtreme Rev.2
0.30 mm
1.70 mm
Scythe Kotetsu
0.35 mm
1.66 mm
Scythe Grand Kama Cross
0.38 mm
1.66 mm
Reeven Kelveros
0.47 mm
1.61 mm
Zalman CNPS9900 MAX
0.16 mm
1.59 mm
Thermalright Silver Arrow
0.32 mm
1.57 mm
Cooler Master Hyper 212 Plus
0.43 mm
1.54 mm
Thermalright Ultra-120 eXtreme Rev.C
0.56 mm
1.52 mm
Zalman CNPS10X Extreme
0.42 mm
1.50 mm

NZXT Kraken X31/X41 (radiator)

0.15 mm

1.07 mm

Testing on larger heatsinks like this one is done on our
LGA1366 heatsink testing platform
, while smaller coolers are tested
on our LGA1155
heatsink testing platform
. A summary of the test system and procedure
follows.

Key Components in LGA1366 Heatsink Test Platform:

  • Intel Core i7-965 Extreme
    Nehalem core, LGA1366, 3.2GHz, 45nm, 130W TDP.
  • Asus
    P6X58D Premium
    ATX motherboard. X58 chipset.
  • Asus
    EAH3450 Silent
    graphics card.
  • Intel
    X25-M
    80GB 2.5" solid-state drive. Chosen for silence.
  • 3GB QiMonda
    DDR3 memory. 3 x 1GB DDR3-1066 in triple channel.
  • Seasonic X-650 SS-650KM
    650W ATX power supply. This PSU is semi-passively cooled. At the power levels
    of our test platform, its fan does not spin.
  • Arctic Silver
    Lumière
    : Special fast-curing thermal interface material, designed
    specifically for test labs.
  • Noctua 140 mm fan (used when possible with heatsinks that fit 140x25mm
    fans)
  • Nexus 120 mm fan (used when possible with heatsinks that fit 120x25mm
    fans)
  • Nexus 92 mm fan (used when possible with heatsinks that fit 92x25mm
    fans)

Key Components in LGA1155 Heatsink Test Platform:

The systems are silent under the test conditions, except for the CPU cooling
fan(s).

Normally, our reference fans are used whenever possible, the measured details
of which are shown below.

Reference Noctua 140mm fan

Anechoic chamber measurements
Voltage
Speed
12V
1250 RPM
28~29 dBA
9V
990 RPM
21 dBA
8V
880 RPM
18 dBA
7V
770 RPM
15~16 dBA
6V
660 RPM
13 dBA


Reference Nexus 120 mm fan

Anechoic chamber measurements
Voltage
Speed
12V
1080 RPM
16 dBA
9V
880 RPM
13 dBA
7V
720 RPM
12 dBA


Reference Nexus 92 mm fan

Anechoic chamber measurements
Voltage
Speed
12V
1470 RPM
17 dBA
9V
1280 RPM
14 dBA
7V
1010 RPM
12 dBA

Measurement and Analysis Tools

  • Extech 380803 AC power analyzer / data logger for measuring AC system
    power.
  • Custom-built, four-channel variable DC power supply, used to regulate
    the fan speed during the test.
  • PC-based spectrum analyzer:
    SpectraPlus with ACO Pacific mic and M-Audio digital
    audio interfaces.
  • Anechoic chamber
    with ambient level of 11 dBA or lower
  • Various other tools for testing fans, as documented in our
    standard fan testing methodology
    .
  • SpeedFan,
    used to monitor the on-chip thermal sensors. The sensors are not calibrated,
    so results are not universally applicable. The hottest core reading is used.
  • Prime95,
    used to stress the CPU heavily, generating more heat than most real applications.
    All instances are used to ensure full stress.
  • CPU-Z,

    used to monitor the CPU speed to determine when overheating occurs.

  • Thermometers to measure the air temperature around the test platform
    and near the intake of the heatsink fan.

Noise measurements are made with the fans powered from the lab's variable DC
power supply while the rest of the system is off to ensure that system noise
do not skew the measurements.

Load testing was accomplished using Prime95 to stress the processor, and the
graph function in SpeedFan was used to ensure that the load temperature is stable
for at least ten minutes. The temperature recorded is the highest single core
reading. The stock fans were tested at various voltages to represent a good
cross-section of airflow and noise performance.

The ambient conditions during testing were 10~11 dBA and 21~23°C.

SOFTWARE

As there are dozens of similarly designed closed-loop water coolers on the market, NZXT has made an effort to differentiate their product with software. The USB cable links up to their CAM utility, giving users the ability to control fans plugged into the two provided headers while also monitoring CPU and GPU temperature, and CPU and memory usage. Fan speed can be regulated as well, either manually, or dynamically based on the temperature of the liquid rather than the CPU, but there is no option to adjust the pump speed.

NZXT claims the pump varies in speed automatically between 2400 and 3600 RPM based on thermal load, but during our time with it, their own software revealed it always ran close to the maximum speed regardless of the temperature. The pump can be slowed down but you have to do it yourself by connecting it to a voltage-controllable fan header and using alternate fan software. However, if you want to know the pump's rotational speed, that information is only available through their utility, which is unfortunate as both the fan and pump speeds it reported fluctuated by a sizable amount. For example, at full speed, using both a tachometer and SpeedFan, we determined the X31's fan to be spinning at a steady 1900 RPM, while CAM suggested it was continually ramping up and down within a range between 1700 and 2400 RPM. The amount of variation is surprising for something so simple.

The fan control options includes manual control between 40% and 100%, two predefined presets, and custom adjustment by tweaking the curve of the fan speed/temperature graph. The more advanced Kraken models (all those except the X31) are equipped with LED lighting on the base and the color can be changed here as well. Furthermore, if you sign up for an account, you can monitor the status of the cooler via the cloud and with an iOS and Android app scheduled to be released next month. We suppose that's the modern thing to do but who really needs to monitor or adjust their desktop cooling when away from home?

CAM need some serious polish but it's also not quite ambitious enough to replicate the full functionality of motherboard software. System and hard drive temperature sensors are no where to be found and fans connected to motherboard headers can't be monitored or controlled. So really, all CAM does is let you play with the LED color and monitor the pump speed. For many users, that's not worth having yet another annoying icon taking up space in the system tray.

STOCK FAN MEASUREMENTS

Specifications: NZXT Kraken X31 Stock Fan
Manufacturer NZXT Power Rating 2.4 W
Model Number RF-FX122-HP Airflow Rating 81.32 CFM (max.)
Bearing Type Hydro Dynamic Speed Rating 800 ~ 2000 RPM
Frame Size 120 x 120 x 25 mm Noise Rating 18 ~ 34 dBA
Hub Size 42 mm Header Type 4-pin PWM
Blade Diameter 114 mm Starting Voltage 4.0 ~ 4.5 V
Cable Length 40 cm Weight 140 g
Corner Type Closed Retail Availability No

Additional notes:

The X31's stock 120 mm fan uses a conservative design with seven large blades with a modest degree of curvature and sharp corners. The blades trail edges line up almost perfectly parallel with the straight struts, and while this typically is undesirable, the fan somehow manages to avoid producing any noticeable tonality. As with most fans paired with liquid coolers, it's a high speed model, rated for 2000 RPM at full tilt.



The stock fan's range according to Fan Xpert2. PWM control on the top, DC control on the bottom.

According to the specifications, the X31 stock fan has a lower limit of 800 RPM and this was more or less confirmed by ASUS Fan Xpert2. Whether it's on PWM or DC control, it can't be reliably run below about 800 RPM. This limits how quiet the cooler can be; it shouldn't matter because water coolers can't be that quiet in the first place due to ever-present pump noise.

Pump Measurements
12V
~3600 RPM
18~19 dBA
9V
~3200 RPM
16 dBA
7V
~2800 RPM
14 dBA
Stock Fan Measurements
Voltage
Speed
12V
1900 RPM
34 dBA
9V
1520 RPM
28 dBA
7V
1230 RPM
22~23 dBA
6V
1060 RPM
18 dBA
5V
900 RPM
14~15 dBA
Measuring mic positioned 1m at diagonal angle from
the center of the heatsink.

Ambient noise level: 10~11 dBA.

At full speed the X31's pump generated 18~19 dBA which is about average for a closed loop liquid cooler, while 9V and 7V brought the SPL down to 16 and 14 [email protected] respectively. The fan has a much wider range, producing a very loud 34 [email protected] and full speed all the way down to a faint 14~15 [email protected] at 5V. To meet our standard of quiet, both the pump and the fan in particular, have be slowed down.

The noise profiles of the two components couldn't be more different. We were blown away by how the 120 mm stock fan sounded. It was exceptionally smooth with no detectable tonality or even a hint of bearing chatter when we held it up right next to our ears. Its superb character also remained consistent throughout its range. Simply put, it's best liquid bearing model we've ever encountered, and right up there with the gold-standard, the Nexus Real Silent case fan. As evidenced by the frequency analysis, it generated a much smoother broadband profile than the pump, which emits an annoyingly harsh buzz and rattle. The only good thing we can say about the pump is it doesn't make any weird gurgling noises like some water coolers we've reviewed in the past.

Specifications: NZXT Kraken X41 Stock Fan
Manufacturer NZXT Power Rating 7.2 W
Model Number RF-FX142-NP Airflow Rating 42.4 ~ 106.1 CFM
Bearing Type Nano Speed Rating 800 ~ 2000 RPM
Frame Size 140 x 140 x 25 mm Noise Rating 20 ~ 37 dBA
Hub Size 42 mm Header Type 4-pin PWM
Blade Diameter 132 mm Starting Voltage < 4.0 V
Cable Length 40 cm Weight 180 g
Corner Type Closed Retail Availability No

Additional notes:

The X41's fan appears to be a higher speed variant of their 1000 RPM FN V2. The rated speed is the same as the X31's stock fan, between 800 and 2000 RPM, but as it's a larger 140 mm model, it produces more airflow and noise. The design is completely different as well, similar to the 14~15 cm fans shipping with Thermalright's large coolers. With rounded leading blade tips, it resembles a torpedo propeller. The casing has been hollowed out near the corners, presumably to reduce weight, and each mounting hole is fitted with rubber pads to reduce vibration.



The stock fan's range according to Fan Xpert2. PWM control on the top, DC control on the bottom.

ASUS Fan Xpert2 revealed a similar effective range on PWM control as the X31's fan, but there was much more leeway under voltage control. This was confirmed by testing with a manual voltage controller which pegged its starting voltage at less than 4V.

Pump Measurements
12V
~3600 RPM
15 dBA
9V
~3200 RPM
13 dBA
Stock Fan Measurements
Voltage
Speed
12V
1960 RPM
43 dBA
9V
1510 RPM
35 dBA
7V
1200 RPM
28~29 dBA
6V
1020 RPM
23 dBA
5V
840 RPM
18 dBA
Measuring mic positioned 1m at diagonal angle from
the center of the heatsink.

Ambient noise level: 10~11 dBA.

Surprisingly, despite the X31 and X41 being seemingly identical except for the size of the radiator and fan, the X41's pump was much quieter, so much so, that we didn't bother checking its noise level below 9V. We doubt the greater area of the larger radiator is responsible for such a discrephancy so we can only surmise that this is due to sample variation. The X41's fan on the otherhand is much louder than its smaller counterpart, as it is larger yet runs at the same speed. The noise is produced was earsplitting at full speed and we wouldn't personally use it at speeds greater than 1000 RPM.

The X41 fan was not quite as impressive as the X31. It sounded fairly smooth, though there was obviously quite a lot of turbulent noise at higher speeds. Its pitch was slightly higher and at the lowest tested speed of 840 RPM, it developed a mild clicking problem which is unfortunate as the fan needs to be slowed down by at least that much in order bring the noise down to a reasonably quiet level. The pump had similar acoustics to the X31, only the volume was greatly reduced. At full speed, it sounded like the X31 pump when undervolted.

TEST RESULTS

The presence of a pump forces us to adjust our testing methodology somewhat. Tests were conducted by varying voltages for both the pump and fan. Some levels were not tested if the fan was obviously going to drown out the pump (or vice versa) by a big margin.

Test Results: NZXT Kraken X31
Pump Voltage
Fan Voltage
Thermal Rise
12V

(18~19 dBA)
12V
38°C
34 dBA
9V
39°C
28~29 dBA
7V
41°C
24 dBA
6V
43°C
21 dBA
5V
46°C
19~20 dBA
9V

(16 dBA)
7V
41°C
23 dBA
6V
44°C
20 dBA
5V
46°C
17~18 dBA
7V

(14 dBA)
6V
44°C
19 dBA
5V
47°C
16~17 dBA
Reference 120 mm Fan (Nexus)
12V

(18~19 dBA)
12V
41°C
21 dBA
9V
44°C
19 dBA
7V
47°C
18~19 dBA
9V

(16 dBA)
12V
41°C
20~21 dBA
9V
44°C
17 dBA
7V
47°C
16 dBA
7V

(14 dBA)
9V
45°C
16 dBA
7V
48°C
15 dBA
Best results for each fan at ~20 dBA and less in bold.

Measuring mic positioned 1m at diagonal angle from
the center of the heatsink.

Ambient noise level: 10~11 dBA.

With the pump running at full speed, the X31 produced middling results with a reasonable 8°C spread between fan voltages of 12V and 5V. As the pump itself produced 18~19 [email protected], the fan needed to be at 5V or lower to generate a noise level we would consider quiet. Slowing down the pump had almost no effect on its cooling proficiency so there's little reason not to; at most, there was a 1°C increase in temperature. The X31 got a boost in efficiency when using our reference Nexus 120 mm fan, lowering the temperature by ~3°C compared to the stock fan emitting equivalent noise levels.

The fan drowned out the pump completely at higher speeds, but at 7V and lower, the buzzing of the pump was clearly audible, at least in our open test environment.

Test Results: NZXT Kraken X41
Pump Voltage
Fan Voltage
Thermal Rise
12V

(15 dBA)
12V
29°C
43 dBA
9V
31°C
35 dBA
7V
34°C
28~29 dBA
6V
36°C
23 dBA
5V
38°C
20 dBA
9V

(13 dBA)
5V
38°C
20 dBA
Reference 140 mm Fan (Noctua)
12V

(15 dBA)
12V
32°C
29~30 dBA
9V
34°C
23 dBA
8V
36°C
20 dBA
7V
37°C
18 dBA
6V
38°C
16 dBA
9V

(13 dBA)
7V
37°C
17~18 dBA
6V
39°C
15~16 dBA
Best results for each fan at <25 dBA in bold.

Measuring mic positioned 1m at diagonal angle from
the center of the heatsink.

Ambient noise level: 10~11 dBA.

Since we began testing CPU coolers with our current configuration, we've rarely seen a thermal rise figure below 34°C, but the X41 managed this at a few different levels. At full pump/fan speed, the result was 29°C, easily setting a new SPCR record, though it generated a ridiculous 43 [email protected] doing so. Interestingly, the X41's worst result of 38°C with both components undervolted, equaled the X31's best result with the pump and fan running at full speed. The X41's larger volume apparently gives it a huge performance advantage over its little brother. The X41 pump is substantially quieter than the X31, so we only tested it at 12V and 9V, but again we saw very little difference between the two. Additionally, except at 5V, the fan's noise output was much greater than the pump, making the pump's poor acoustics a complete non-factor.

Our reference fan proved to be a better match for the cooler once more, with the Noctua NF-P14 beating out the stock 140 mm fan by 2°C. NZXT's fans have excellent acoustics but they simply aren't as effective. It should also be noted that if you plan on replacing the fans, the X41 radiator only has 140 mm mounting holes which many 140 mm fan models lack. We had to use long plastic twist-ties threaded through the radiator coils to keep the reference fan in place for these tests.

HEATSINK COMPARISON TABLE

°C Rise Comparison: CPU Coolers with Single Stock Fan (Any Size)
20
19
18
17
16
15
14
13
12
11
Scythe Kotetsu
        38  
41
  42  
NZXT Kraken X41

(ref. 140mm fan)
36
 
37
39
       
Thermalright Archon SB-E
39
         
40
   
43
Thermalright HR-02 Macho
 
39
     
40
41
 
43
 
Scythe Mugen 4
       
40
   
42
 
45
Noctua NH-U14S
 
38
 
40
   
43
   
NZXT Kraken X41
38
                 
be quiet! Shadow Rock Slim
 
40
   
41
 
42
   
Noctua NH-D15
39
   
41
   
44
   
Scythe Yasya
   
40
       
43
   
Cogage TRUE Spirit 1366
     
41
 
43
 
46
 
Zalman CNPS10X Quiet
40
       
42
 
47
 
Scythe Ashura
 
42
     
44
     
Cooler Master Hyper 212 Plus
   
41
       
44
54
 
Silverstone Argon AR03
   
43
         
48
Scythe Ninja 3
   
44
       
46
   
SilverStone Argon AR01
   
44
         
50
Phanteks PH-TC12DX
   
44
     
47
     
Titan Fenrir
   
45
 
47
     
NZXT Kraken X31

(ref. 120mm fan)
      44
45
48        
SilverStone Tundra TD03
   
44
46
           
Antec Kühler H20 620
 
44
     
47
     
NZXT Kraken X31
44
   
47
         
Zalman CNPS9900 MAX
45
     
47
 
49
     
GELID Tranquillo Rev.2
 
48
 
49
   
50
     
20
19
18
17
16
15
14
13
12
11

Historically, liquid coolers have not that fared well on our test platform, and the X31 is no exception. On our efficiency chart, it landed just below the SilverStone Tundra TD03 and Antec Kühler H20 620, and well behind more than a dozen traditional heatsinks. The X41 on the otherhand was an order of magnitude better, almost cracking into the top five. With the help of our reference fan, it contended with the Scythe Kotetsu for the top spot.

MP3 SOUND RECORDINGS

These recordings were made with a high
resolution, lab quality, digital recording system
inside SPCR's
own 11 dBA ambient anechoic chamber
, then converted to LAME 128kbps
encoded MP3s. We've listened long and hard to ensure there is no audible degradation
from the original WAV files to these MP3s. They represent a quick snapshot of
what we heard during the review.

These recordings are intended to give you an idea of how the product sounds
in actual use — one meter is a reasonable typical distance between a computer
or computer component and your ear. The recording contains stretches of ambient
noise that you can use to judge the relative loudness of the subject. Be aware
that very quiet subjects may not be audible — if we couldn't hear it from
one meter, chances are we couldn't record it either!

The recording starts with 5 second segments of room ambiance, then the fan
at various levels. For the most realistic results, set the volume so that
the starting ambient level is just barely audible, then don't change the volume
setting again.

FINAL THOUGHTS

Of the two Krakens we tested today, the X41 is clearly the more attractive option. It's the first liquid cooler we've reviewed with a 140 mm radiator and the extra volume seems to do wonders for cooling proficiency. The smaller X31's performance was more or less equivalent to previously tested units with 120 mm radiators, that is to say, poor compared to the better air-cooled heatsinks available on the market at equivalent noise levels. There seems to be an invisible performance ceiling with these coolers that can't be broken without increasing the heat dissipation area beyond that of a 120 mm fan placement. The bigger X41 busted through this barrier with ease while using the same sized base, putting it in contention with elite heatsinks paired with a single fan.

It certainly didn't help that the X31's pump was inexplicably louder than the X41, but still, a 2~3 dB difference wouldn't be enough to make it competitive with high-end solutions. It's a shame the X31 didn't fare better as its stock fan has a phenomenal sound — we'd love to see NZXT sell these fans separately as accessories. The X41's fan also has fairly pleasant acoustics, but its 2000 RPM top speed is quite high for a 140 mm model. To make it quiet, it has to be slowed down to close to the minimum PWM-controllable speed. This is an issue with most liquid coolers as they are typically paired with high speed fans in order to appeal more to enthusiasts; with the high top speed comes a high minimum speed. The X41's fan can go lower with voltage control but that may be inconvenient depending on how many controllable headers are available, especially if you use one to undervolt the the pump.

NZXT is pushing the its CAM software as a big selling point for its water cooling units, but the current version isn't compelling. CAM can't slow down the pump, can only control the two fan headers emanating from the base of the cooler, and the speeds it reports fluctuate by a large degree. Its functionality isn't extensive enough to completely replace motherboard utilities like Fan Xpert or EasyTune, making it effectively redundant unless you want to monitor the pump speed or change the LED color. Its cloud capabilities are a sign of forward-thinking but it's really just window dressing. Liquid coolers are fairly cost-prohibitive and CAM doesn't offer much in the way of added value.

The NZXT Kraken X31 is selling for US$75 but as it performs similarly to similarly sized liquid coolers, we can't recommend it. Dozens of traditional options exist that deliver better cooling at a more affordable price. It might be good option for a smaller system with a limited CPU cooler height requirement but that's the only scenario where it's worth consideration. The X41 is a far superior product though it does cost a bit more at US$100. We're not crazy about the price which keeps it off our short list, but the same can be said about plenty of comparable air coolers as well. Price notwithstanding, we'd be content with the X41 in one of our PCs: The combined pump/fan noise is low without any major fiddling, and it provides elite cooling performance.

Our thanks to NZXT
for the Kraken X31 and X41 CPU cooler sample.

* * *

SPCR Articles of Related Interest:

Noctua NH-D15: Update to an Icon
Scythe Kotetsu CPU Cooler: A Compact King
be quiet! Shadow Rock Slim CPU Cooler
Thermalright HR-22 CPU Heatsink
Noctua NH-U14S Slim 140mm Tower Cooler
SilverStone Tundra TD03 Liquid CPU Cooler

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