Cooler Master Tempest GZ2711

Introduction

It seems like in a very short period of time we’ve gone from not having any OLED monitors available, to there being lots of competition in the market. No segment is more crowded than the 27″ 1440p range, and it feels like every manufacturer is releasing a screen in this space. Cooler Master have produced some mostly good LCD monitors over the last few years and we’ve been impressed by some of their Mini LED models that we’ve reviewed like the GP27U and GP27Q for instance. Now, they are venturing in to the OLED monitor market for the first time with the release of their Tempest GZ2711, a 27″ monitor with a 2560 x 1440 resolution and 240Hz refresh rate. It’s a little over a year since the first monitors of this spec were released to market (the LG 27GR95QE being the first) and so Cooler Master are coming to the party quite late, but entering with a competitive price point, and providing a few extra features that others may be lacking in order to compete. The GZ2711 has USB type-C connectivity, PiP and PbP support and integrated speakers for instance.

But how does it perform? Can it compete with the wide range of competing models in this space? We will put the new screen through our testing to find out.

• Related content: Check out a round-up of all Cooler Master monitors, and their planned future roadmap here

Where to Buy

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Key Specs and Features

• 27″ screen size (accurately 26.5″) with 16:9 aspect ratio and flat screen
• 2560 x 1440 resolution (1440p)
• LG.Display WOLED panel (LM270AHQ-ERG2)
• 240Hz refresh rate and 0.03ms G2G response time spec
• Adaptive-sync for variable refresh rates (VRR) including AMD ‘FreeSync Premium’ certification
• Wide colour gamut covering 98.5% DCI-P3 and 95.3% Adobe RGB
• 2x DisplayPort 1.4 (with DSC), 2x HDMI 2.1 and 1x USB type-C (with DP Alt mode and 96W power delivery) connections
• Picture in Picture (PiP) and Picture by Picture (PbP) support
• 2x 3W built-in speakers, 2x USB 3.0 data ports and 1x audio output
• Fully adjustable stand with tilt, height, swivel and rotate adjustments

Design and Features

The Cooler Master Tempest GZ2711 comes in a sleek overall design with a 4-side “borderless” panel where there’s only a thin plastic edge, but a black panel border before the image starts. This measures ~9mm along the top and sides of the screen, and ~12mm along the bottom edge (assuming you have the screen shift function disabled). There is a protruding “chin” on the bottom of the screen as you can see from the images above, with the OSD control joystick and power on/off button located on the back. A small Cooler Master logo glows here when the power is turned on, or this can be turned off in the OSD menu if you want.

The back of the screen is encased in a matte black plastic with a very thin profile around the top and sides thanks to the OLED panel (which doesn’t need a backlight). The central section is chunkier as that’s where the connections and electronics are housed. The screen has an external power supply brick by the way.

The stand has a quick release attachment to the back of the monitor or it can be removed in favour of 100 x 100mm VESA mounting support if you would rather arm- or wall-mount the screen. There are two subtle and small RGB lighting strips on the back of the screen as shown above. The RGB lighting is accessed quite oddly via the ‘ambient light’ setting in the OSD, which we originally mistook for an ambient light sensor control – but it’s not. You can disable these in the menu if you want as well.

The monitor has a fairly thin, but strong metal arm and metal foot in the shape of the Cooler Master logo. This sticks out a fair way in front of the panel itself as you can see above so make sure you have enough desk space to position your keyboard and mouse. We’d have liked a smaller footprint really here. There’s a removable cable tidy clip on the back of the arm as well.

The stand provides a full range of ergonomic adjustments with tilt, height, swivel and rotate available. The tilt is a little stiffer than the others to use, but all provide smooth and easy adjustments. The screen remains stable overall thanks to the strong stand, although there’s a little bit of wobble if you re-position the screen.

The back of the screen features all the connections. There’s 2x HDMI 2.1 ports (24Gbps bandwidth), 2x DisplayPort 1.4 and 1x USB type-C (with DP Alt mode, data and 96W power delivery). There’s also an audio output, 1x USB-B upstream port and 2x USB A downstream ports here. This provides a decent set of connections, although it could have been useful to have some USB and audio connections on the side of the screen perhaps for easier access.

You can see here as well the OSD control joystick toggle that is on the back of the “chin” section, as well as a power on/off button.

The OSD is controlled entirely through the joystick toggle. This is reasonably easy to use, although sometimes it’s not very intuitive when you drill in to different sub-sections, select an item or want to go back a stage. Some settings are a bit fiddly to use in practice, mostly in HDR operation which we will talk about more later. It’s also a bit slow and sluggish in places. The menu provides a modest set of options to configure.

Brightness and Contrast

The only change we made to the OSD menu was to disable the ‘logo luminance adjustment’ care feature for these tests, so as not to impact the measurements.

The GZ2711 has an Automatic Brightness Limiter (ABL) feature active during SDR and desktop use which means that as the measurement window size increases, the luminance is reduced. For the smallest window sizes the luminance can reach up to 335 nits when the brightness control is set to 100%, but this drops off quite significantly by the time you reach 25% APL area size, where it only reaches 182 nits and then stabilizes from there for any larger APL.

If you lower the brightness setting in the OSD menu, the same pattern applies as you can see from the graph above. In practice this means that you get varying luminance depending on your content and window sizes, which can be distracting during desktop usage and with office applications.

There was no change to this ABL dimming behaviour in any of the other preset modes including the ‘text’ or ‘web’ settings. Changing the ‘ECO’ setting in the menu also had no impact to the ABL trend, it just reduced your maximum luminance a little for the sake of reducing power consumption. This was disappointing as it means that there is no “uniform brightness” mode available on this monitor for desktop usage, which is actually rare in the OLED monitor market nowadays. All the other new OLED screens we’ve tested in recent months operate with a uniform brightness in these situations meaning you get a consistent and stable luminance no matter what the content in SDR. Cooler Master have definitely missed a trick here by not offering a mode like that here.

• Useful reading – OLED Dimming Confusion – APL, ABL, ASBL, TPC and GSR Explained

Black Depth, Shadow Detail and Contrast

One of the key benefits of an OLED panel is the fact it is capable of generating true blacks and a basically infinite contrast ratio. Each pixel can be fully turned off individually, and there’s no need for backlight local dimming here like there is on LCD’s. As a result, the black depth and contrast ratio can surpass all LCD panel technologies including VA panels by a long way. Blacks look inky and deep, and you get local contrast between different areas of an image.

Your ambient lighting may have some impact on perceived contrast ratio as it does with all screens; with matte AG coatings like this resulting in a larger drop in black depth than glossy alternatives – although they are far better at handling reflections so there is a trade-off there. Being built around an LG.Display WOLED panel it does not suffer in the same way as competing QD-OLED panels do which see more noticeable raised blacks due to their different panel structure. As a result this panel is better suited to brighter room environments and day time usage than competing QD-OLED models.

• Related content: The OLED Black Depth Lie – When Panel Type and Coating Matters

The near black shadow detail was moderate, but it was hard to pick out very dark grey shades in this test image with box 5 being the first that was easy to distinguish before calibration in SDR mode. This is something that can often be an issue on OLED panels. There is a ‘black stabilization’ option in the OSD menu which can be turned up one step from 50 to 60 that helps a bit, making the darker shades 3 – 5 a bit brighter and easier to pick out. Higher settings that this just seem to impact the lighter grey shades so provide no additional benefit with near-black shadow detail.

Like most OLED screens there is a minor fluctuation of the backlight, and in this case it operates in sync with the refresh rate, whatever you have that set at. Above it’s operating at 240Hz so there’s a small fluctuation every ~4.17ms. You can see on the graph above that the 0V would be an “off” state, so the amplitude of this fluctuation is minor, and does not produce any visible flickering or anything like that in practice. It’s not the same as PWM on an LCD monitor where the backlight is rapidly switched fully off and on when trying to dim the brightness level. Obviously being an OLED panel there is no backlight here anyway, and this minor fluctuation didn’t cause us any problems in real use and would be considered flicker free.

Default Setup

The screen comes out of the box in the ‘standard’ preset mode and with brightness set to 100. You can probably spot the immediate issue with the default setup and that is the very skewed gamma curve on the left hand side. The gamma is far too high in dark to mid greys which crushes these shades and causes some loss of shadow detail. The gamma is then a little low in the lightest grey shades near to which which results in some lost shade detail. The screen is set in the 2.2 gamma mode by default, and we experimented with the other available settings but none addressed this problem and if anything just made it far worse. None of the modes are really very close to their intended gamma at all.

We fed this back to Cooler Master when we first received the screen in case it was an issue with our sample, but a replacement unit shows the same issue and so we can only conclude that this is a large inaccuracy with the factory calibration of gamma. We have fed this back again to CM for investigation.

Thankfully the colour temperature is a lot better, with an average 6599K across the greyscale, being only 2% slightly too cool, but this shouldn’t be noticeable in most situations. The lightest grey shades and white is where the red channel drops a little lower than intended as you can see from the middle RGB balance graph, resulting in this slightly too cool appearance and a white point which was also 2% out from our target. No real issues though here in this regard. The greyscale accuracy overall was moderate (dE 3.4 average), with some high errors in the middle grey shades resulting from the poor gamma curve (reaching up to dE 7.1).

The screen has a wide colour gamut with 126.6% relative coverage of the sRGB space measured. This isn’t as high as competing QD-OLED screens – for instance the MSI MPG 271QRX which is a 27″ 1440p equivalent can reach ~141% sRGB coverage thanks to the use of Quantum Dots on the panel. Here the wide gamut leads to moderate over-coverage in green and red shades, making those colours look over-saturated and leading to very high errors (dE 5.5 average) when displaying SDR / sRGB content. This is the a common story for any wide gamut screen and should be expected, although it’s not always as high as this. If you want to work more accurately with SDR content you will need to be able to calibrate and profile the screen yourself as the provided sRGB emulation mode also has issues which we will discuss in a moment.

The bottom section compares the colours against several wide colour gamut reference spaces, and you can see that the panels colour space matches the DCI-P3 reference space, used for a lot of HDR content, very nicely. We had a 97.5% absolute coverage of that colour space (close to the 98.5% quoted), with only very minor over-coverage to reach 101% relative coverage. DCI-P3 is the closest match to the native gamut of the screen but the accuracy of colours within that colour space is sadly no better, with an average dE of 5.6 measured. This was unusual, as normally we see these screens offer good DCI-P3 colour accuracy where the available gamut matches closely. This suggests there is a poor factory calibration on this screen in the native gamut mode. You would need to be able to calibrate the screen yourself if you want more accurate performance in the DCI-P3 colour space using this ‘standard’ mode, but at least the colour space coverage is there to support it.

There is also pretty decent coverage of the Adobe RGB colour space with 96.7% coverage measured (slightly better here than the 95.3% quoted in the spec), which makes it viable to use this screen for content specifically in that colour space if you want, although you’d need to be able to profile the screen yourself using a calibration tool to more accurate map the colours back to that reference space as there are issues with the provided Adobe RGB emulation mode that we will discuss later.

sRGB Emulation Mode

According to the product page the screen has been factory calibrated for colour accuracy, with a dE <2, in the sRGB mode. This is available in the OSD menu via the ‘colour mode’ setting so we tested this mode as well:

We had the same problem in this mode as the ‘native’ colour space, in that the gamma curve is way off the target. You can see is is far too high in dark to mid greys which compresses those tones and results in a loss of shadow detail. Even the average gamma cross the whole greyscale was calculated at 2.47 here, a long way off the 2.2 target you’d normally expect. Cooler Master don’t list any other criteria for their factory calibration other than a colour accuracy target (dE < 2) which we will come on to in a moment, but you’d have expected a reliable 2.2 or sRGB gamma curve here really. The gamma configuration is poor in this mode again which is disappointing.

Like in the native mode, the colour temp across the greyscale was good, being only a minor 2% too warm now in this mode including for the white point which was measured at 6500K. Greyscale accuracy was impacted by the poor gamma again.

Colour accuracy in this mode was a disaster unfortunately. Firstly, while the native gamut of the panel has been clamped back to reduce the over-coverage of the sRGB colour space, it goes too far and we now have only an 85.5% absolute coverage of this reference space. You can see that in blue and red shades the coverage is too low. We also checked the available ‘Rec.709’ mode in the menu which delivered the same over-clamped colour space.

In this mode you have access to some of the OSD settings, including importantly brightness. The colour temp control, and therefore the RGB gain controls are not accessible but you have access to hue and saturation settings if you wanted to make a few tweaks. The gamma setting is accessible in the menu, but it doesn’t do anything while using the sRGB emulation mode for some reason. The accuracy of sRGB colours in this mode is still really bad with a dE 6.6 measured.

We’ve fed this back to Cooler Master, but it appears that there is a problem with the factory calibration and this mode is basically unusable given the terrible gamma, over-clamped colour space and poor colour accuracy. That only leaves you with the option of profiling and calibrating the screen yourself if you want to work with sRGB / SDR content more accurately within colour aware applications.

Adobe RGB Emulation Mode

Unfortunately it was the exact same story in the Adobe RGB mode. Really poor gamma which was far too high for dark and mid grey shades, over-clamping of the intended colour space (reaching only 81.3% coverage) and bad colour accuracy for Adobe RGB colours (dE 7.4 average). This means that again your only option if you want to work more accurately with Adobe RGB content in that colour space is to profile and calibrate the screen yourself.

We’ve not included the graphs here, but it’s the same story for the DCI-P3 mode too, it’s just way off for accuracy.

Calibration

The screen was profiled to 2.2 gamma, 6500K colour temp and to the sRGB colour space. The screen was left in its native wide gamut mode, but this profile will be used in colour-aware applications (e.g. Photoshop) to map back to sRGB in this instance. You can find our calibrated settings and ICC profile in our ICC profile database now.

We expected calibration to be able to resolve all the problems with the default setup but unfortunately this was not possible. We did at least correct the gamma curve using this approach to 2.2, and also tweaked the colour temp to bring that in line with our 6500K target. Unfortunately it was not possible to correct the colour accuracy fully for some reason. We tried multiple approaches, even calibrating within the ‘native’ and the ‘user’ colour temp modes but both were the same. There were improvements to gamma at least which had been a major problem before, but it was disappointing to not be able to fully correct the colours. We can only conclude that the best you will get out of this screen, even with professional calibration, is moderate-to-poor colour accuracy unfortunately.

Office and General Usage

The 27″ screen size with a 2560 x 1440 resolution is very common in the market nowadays and provides a comfortable text size without the need for any operating system scaling, and a decent desktop area in which to work. It’s a comfortable option and will suit many people.

The panel has the standard matte anti-glare (AG) coating that we’ve seen on previous 27″ 240Hz WOLED monitors to date (and other larger 34″ and 45″ WOLED panels too for that matter). This is a little more grainy in appearance than modern LCD IPS panels, and doesn’t look quite as clean and clear as a result. It does a good job of handling glare and reflections though, better than competing QD-OLED panels in this regard so it more well-suited to brighter room conditions, daytime use and perhaps office environments. We prefer the semi-glossy coating finish of QD-OLED panels overall at the moment, but everyone’s use case will be different. We should also note here that there are plans to release fully glossy 27″ 240Hz WOLED monitors as well soon, like the recently announced Asus ROG Strix XG27AQDMG.

The screen uses an LG.Display WOLED panel which has a RWBG sub-pixel layout, and this is the same as all the previous 27″ 240Hz WOLED panels on the market so far. This sub-pixel layout causes some issues with text clarity in Windows and office applications, where you get some fringing in certain situations, and text doesn’t always look as sharp as you might expect. This isn’t terrible or anything, and if you’re primarily going to be using the screen for its intended uses of dynamic content, gaming and multimedia then there shouldn’t be any major problems. If you’re bothered by text sharpness, then as with the other WOLED screens we’ve reviewed so far, we’d advise some caution. This is another situation where we prefer the competing QD-OLED panels in this segment, as they offer better text clarity and less fringing on text.

It’s good to see some extra features like a USB type-C connection (with DP Alt mode, data and a high 96W power delivery), as well as Picture in Picture (PiP) and Picture by Picture (PbP) support for handling multiple inputs on the screen at once. There were also some basic 2x 3W integrated speakers which might be ok for the odd mp3 or YouTube video, or perhaps for handling external devices, but obviously aren’t very powerful for gaming or movies. There’s an audio output connection though to hook up to something more powerful and pass the sound through the monitor like when using the HDMI connection.

The screen is missing some other common, modern features like a KVM switch function in case that would have been useful to you. We would have perhaps liked to have seen some quick-access USB ports on the side of the screen (there’s only 2 on the back), an ambient light sensor and perhaps a human motion sensor to turn the screen off when it’s not being used. That could be particularly useful on an OLED panel like this to help mitigate image retention.

Speaking of which, the GZ2711 has a fairly simple set of OLED care options. There’s a familiar pixel clean / refresh function, a screen shift (settings for on or off) and a ‘logo luminance adjustment’ (settings for on or off). While it’s not listed in the OSD menu we did also notice that there was an ASBL (Automatic Static Brightness Limiter) active which dimmed the screen a bit if you left it static for a long period of time – and then brightened it again when you change something on the screen. We never noticed this kicking in during any normal desktop applications or usage, only when we left the screen alone for an extended period of time so this is not likely to cause any issues we don’t think. We would expect the GZ2711 to carry the same 3 year warranty as their other monitors, but there’s no reference to burn-in cover on their product page or warranty page at this time which is something to keep in mind when other manufacturers are now offering this for their OLED screens.

The spectral distribution of the panel at a calibrated 6500K is shown above, with the blue peak measured at 455 nm wavelength with a 34.77% blue light percentage. This means that it’s just outside of the supposedly harmful range of 415 – 455nm defined by Eyesafe and so can fit within their Eyesafe certified products.

There is a ‘Blue Light Filter’ setting in the OSD menu which offers a slider between 0 and 100, and which makes the image progressively warmer in appearance as you increase that. This gives you a very finite control though over the temp if you want to tweak things, although it’s a bit of a pain to enable and disable in this way unless you wanted to leave it active all the time. If you want to quickly and easily switch between different configurations then the ‘View mode’ presets may be a better option. Nevertheless, at its maximum setting of 100, and from a calibrated 6500K state (at 0), the screen reaches a 4972K white point.

Gaming

The screen uses an OLED panel which is well-known for its near-instant response times. As a result it does not need to use overdrive technology in the same way as a desktop LCD panel would, and there aren’t any controls for the response time or overdrive in the OSD menu. We are reliant on Cooler Master’s tuning of the response times. CM, like other OLED display manufacturers quote a very low 0.03ms G2G response time in their spec, and while true <1ms G2G should be expected from this technology this is a little over the top.

The OLED panel provides super-deep blacks and a basically infinite contrast ratio which is of course excellent for gaming too. The per-pixel level dimming and high contrast ratio also make it well suited to HDR gaming in theory, and we will measure HDR performance a bit later. The very wide viewing angles of this technology are also excellent and make the screen suitable for viewing from many different positions if you need. These wide viewing angles importantly include the freedom from things like the pale/white “IPS glow” that you get on darker content on that common LCD technology. There’s none of that here on the OLED panel.

(at native resolution)	Refresh Rate
Maximum Refresh Rate DisplayPort	240Hz
Maximum Refresh Rate USB type-C	240Hz
Maximum Refresh Rate HDMI	240Hz
VRR range	48 – 240Hz
ClearMR certification tier

The screen has a native 240Hz refresh rate which is very familiar now in this 27″ 1440p OLED segment. This provides excellent motion clarity (demonstrated later), and can support high frame rates too, reducing overall system latency compared with lower refresh rate screens. 

For some reason Cooler Master list the HDMI connection as only supporting up to 144Hz on their website, but our testing achieved 1440p @ 240Hz without issue from a PC. The HDMI 2.1 connections used here are restricted to 24Gbps bandwidth (not the full 48Gbps) but with DSC active they can handle that combination fine, even up to 12-bit colour depth. Keep in mind the panel is a native 10-bit panel only though.

	VRR capabilities and Certification
AMD FreeSync certification	FreeSync Premium
Native NVIDIA G-sync module
NVIDIA ‘G-sync Compatible’ certified
VESA ‘AdaptiveSync’ certification
HDMI-VRR (consoles via HDMI 2.1)

Cooler Master’s website says that the screen has been certified under the AMD ‘FreeSync Premium’ scheme, although we noticed that it is not yet listed on AMD’s database. It’s not uncommon for there to be a delay with that though. It hasn’t been certified under any of the other common schemes.

VRR flicker is an inherent problem on all OLED screens, but whether or not you will experience problems with it during your usage is very hard to predict. It really depends on your system, frame rates, game, scene etc. We are working on some future testing approaches that might help measure this, but we want this to be a meaningful representation of real-world experience as much as possible and that is tricky to achieve.

	Other Features
NVIDIA DSR / DLDSR support
Black Frame Insertion (BFI)
Gaming extras	Crosshair, FPS counter
Emulated gaming sizes	4:3, 5:4, 16:9, 16:10

We tested support for NVIDIA DSR / DLDSR which can sometimes work on monitors with DSC (Display Stream Compression), but not always. That was available here and so could allow you to increase the input resolution above the panel’s native 1440p if you want, which could improve image detail and quality. There’s no need to disable DSC or anything here (although there is a setting for that in the OSD menu as well!) as it works fine by default. It would have been nice to have seen BFI available on this model, which is starting to appear on some OLED monitors now from Asus, but that is not offered on this display.

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Our thanks to the following manufacturers for support in the build of our new test system:

	AMD Ryzen 9 7950X | Buy AMD Ryzen 9 CPUs here on Amazon
	Asus ProArt B650-Creator | Buy Asus B650 motherboards here on Amazon
	Corsair DDR5 RAM | Buy here on Amazon
	Corsair H100i Elite Capellix AIO cooler | Buy Corsair coolers here on Amazon
	Corsair iCUE RGB Elite Fans | Buy here on Amazon
	NVIDIA RTX 3090 | Buy NVIDIA RTX graphics cards here on Amazon

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Response Times

As discussed in our detailed article about Response Time Testing – Pitfalls, Improvements and Updating Our Methodology we are using an improved and more accurate method for capturing G2G response times and overshoot, based on figures that are more reflective to what you see visually on the screen in real-World usage. Our article linked above talks through why this is better and how we arrived at this improved method in much more detail.

The above G2G response times are consistent at all refresh rates, including 240Hz, 120Hz and 60Hz and during VRR situations with changing frame rates. Thanks to the QD-OLED panel the response times are super-fast and near-instant, with an average of only 0.47ms G2G measured. The best case was an incredibly impressive 0.33ms and the overall response times were as expected from an OLED panel.

All transitions can keep up easily with the frame rate demands of 240Hz, and in fact this screen could comfortably keep up with >1000Hz if the panel could support it! Let’s hope OLED refresh rates are driven much higher in the coming years, as it’s a really well suited technology for that. We already know there are plans to produce 27″ panels up to 480Hz so higher refresh rates are definitely coming! There is also no visible overshoot evident which is great news too, so overall there was nice and clean pixel transition times.

Motion Clarity – Pursuit Camera Photos

We captured some pursuit camera photos of the screen at a variety of refresh rates, designed to capture real-world perceived motion clarity. This gives you a good indication of how the screen looks in real use, beyond raw measurements.

Despite the amazing pixel response times you still get large amount of blur at 60Hz due to the sample-and-hold nature of the OLED screen, you can’t expect miracles just because it’s got fast response times. There are major and obvious benefits in motion clarity as you increase to 120Hz high refresh rate mode, and this brings it on par with 120Hz OLED screens such as the popular 42″ sized displays like the LG 42C2 and LG 42C3 TV’s, and the Asus ROG Swift PG42UQ.

Like with other 240Hz OLED screens we’ve tested, moving up to 240Hz offers another significant and noticeable improvement in motion clarity, and the moving image is now sharper and cleaner. Tracking of moving content is now much easier and clearer. This really was excellent motion clarity and very impressive. If you can push the screen up to 240fps in your games, which will be a challenge of course in many situations, you will benefit from excellent clarity and smoothness as well as improved system latency due to the higher frame rate supported. There is no overshoot or any associated artefacts or trails at any refresh rate like you might get on LCD screens which was excellent. The motion clarity will be the same as the other 240Hz OLED monitors in the market, unsurprisingly given they are all using 240Hz OLED panels. This motion clarity is very similar to a good 360Hz LCD panel so is very impressive.

Here’s some further comparisons of the motion clarity with other common OLED refresh rates, including as well the latest 360Hz panels which are currently available in 27″ screen size at the moment using competing QD-OLED panel technology. We’ve already reviewed a couple of those in the form of the Dell Alienware AW2725DF and MSI MPG 271QRX which are well worth a look in this 27″ OLED segment.

Lag

Read our detailed article about input lag and the various measurement techniques which are used to evaluate this aspect of a display. The screens tested are split into two measurements which are based on our overall display lag tests and half the average G2G response time, as measured by our oscilloscope. The response time element, part of the lag you can see, is split from the overall display lag and shown on the graph as the green bar. From there, the signal processing (red bar) can be provided as a good estimation of the lag you would feel from the display. We also classify each display as follows:

Lag Classification (updated)

• Class 1) Less than 4.17ms – the equivalent to 1 frame lag of a display at 240Hz refresh rate – should be fine for gamers, even at high levels
• Class 2) A lag of 4.17 – 8.33ms – the equivalent of one to two frames at a 240Hz refresh rate – moderate lag but should be fine for many gamers. Caution advised for serious gaming
• Class 3) A lag of more than 8.33ms – the equivalent of more than 2 frames at a refresh rate of 240Hz, or 1 frame at 120Hz – Some noticeable lag in daily usage, not suitable for high end gaming

There is an extremely low lag on the GZ2711 measured at 0.50 ms total display lag, and leaving us with only 0.38 ms of estimated signal processing lag. This is perfectly fine for competitive gaming. This is a bit higher at 60Hz refresh rate, measured at 8.0ms total display lag but actually pretty good compared with many screens. Remember that it is the lower number (0.50ms) that will be relevant for VRR gaming as well, even where frame rates drop. The 60Hz figure is only applicable for fixed 60Hz input sources.

Console Gaming

	Console Gaming
Native panel resolution	2560 x 1440 (1440p)
Maximum resolution and refresh rate supported	1440p @ 120Hz
Virtual 4K support
4K at 24Hz support
4K at 50Hz support
HDMI connection version	2.1
HDMI connection bandwidth	24 Gbps
HDMI-CEC auto switch
HDMI-VRR (over HDMI 2.1)
Auto Low Latency Mode (ALLM)
HDR10 support	PS5 only
Dolby Vision HDR support

The screen has only a 1440p native resolution and will run at 1440p @ 120Hz from modern games consoles. Unfortunately the screen does not support a Virtual 4K input, and so that leaves it with some glaring gaps for modern consoles. Some people may have wanted to input 4K resolution here to help improve image detail perhaps (like you can simulate with NVIDIA DSR for instance), but more importantly the Xbox Series X can only operate in HDR mode when it is outputting a 4K resolution. Without that option even being available here, it means from an Xbox you won’t be able to game in HDR, which is obviously a massive gap for an OLED monitor! This limitation does not apply for PS5 which can run HDR at 1440p thankfully.

HDR

Being an OLED panel, the GZ2711 is well equipped to handle HDR content from a hardware point of view with its per-pixel level dimming allowing for true blacks, a basically infinite contrast ratio and the avoidance of all blooming and halos. In these regards it can easily surpass any Mini LED backlit LCD monitor. However, it cannot reach the same luminance levels as Mini LED screens, and its brightness will also lower as the content on your screen changes and the APL increases which is normal on this technology. This is one key area where Mini LED screens can look brighter and deliver a more impactful HDR experience.

Being a WOLED panel it doesn’t suffer from the same raised blacks issue that QD-OLED panels do in brighter room environments, although the matte anti-glare (AG) coating does cause light to be diffused more across the panel and therefore black depth isn’t as strong as on glossy panels. On the other hand, this coating is far better at handling glare and reflections than glossy panel coatings so you need to weigh up which is more important to you, and consider your ambient lighting and room conditions. We discussed the handling of black depth and compared matte and glossy coatings on OLED panels a lot more in our article here.

HDR Operation

HDR operation on this screen is really poorly thought out. When you’ve enabled HDR from your input device / Windows, you also need to go in to the OSD menu of the monitor and enable the ‘HDR10’ setting, changing it from its default ‘off’ setting to ‘auto’. The screen will then switch in to HDR mode for you. Without that step, the image looks really washed out and dull so that’s initially a shock when you go to use HDR.

The other more annoying issue is that the brightness control seems to be universal for both SDR and HDR modes. That means that if you’ve lowered brightness in SDR, which you almost certainly will have to reach a comfortable brightness level, that same setting carries through when you enable HDR. That in turn reduces you peak brightness potential in HDR, and you have to manually change the brightness setting back up to the maximum 100 to get the full potential. The brightness setting should be remembered independently between both modes, or just locked to 100 in HDR like most manufacturers do. There are no HDR preset modes available and no access to the colour temp or RGB channels so we are entirely at the mercy of Cooler Master’s configuration here…which is unfortunately a big problem as you’re about to see.

PQ EOTF Tracking and Greyscale

After the dismal configuration in SDR we had hoped that perhaps HDR mode would be better. It wasn’t. The middle section shows that the colour temp of HDR mode is far too cool, reaching up to 9130K for white, and being a whopping 40% out from our target of 6500K (D65). It looks like Cooler Master have just left the panel operating at its native colour temperature, and there’s been no attempt to configure this to a more sensible and typical 6500K. The image looks really blue and cool next to a calibrated D65 display.

On the right hand side you can see that the tracking of the PQ curve (at 10% APL here) is also poor. It’s too low in the darkest grey shades in the bottom left-hand corner of the graph, resulting in some crushing of shadow detail and loss of tonal values. In dark-to-mid grey shade (20 – 70) the curve is too high compared with the yellow target line, showing that the luminance of these grey shades is higher than intended and causing some washout of these shades, and loss of detail in lighter scenes. The poor PQ tracking and overly cool colour temp result in a terrible greyscale accuracy with dE 9.2 average measured. Unfortunately that’s not the end of the problems…

HDR Brightness

Peak White Luminance

If we look at the common peak white luminance measurements you can see some further issues. The panel can reach up to a reasonably high 861 nits peak white luminance for the smallest APL % which is decent, but tails off as expected due to the Automatic Brightness Limiter (ABL), as the Average Picture Level (APL) increases. That’s normal for any OLED. The problem is that for the largest APL the luminance drops very low, down to 79 nits in fact at 100% APL. This is unnecessarily low as we had seen the screen reach 182 nits in SDR mode at 100% APL when brightness was set to 100%. There’s no need for it to be dimmed so aggressively here in HDR mode. That has a knock on impact to the brightness of the image in HDR for brighter scenes (high APL) which are darker than they needed to be.

To add more measurements and data to our HDR testing we are now introducing some new sections which will help provide a more complete and accurate view of HDR luminance performance in real usage, across a much wider range of test situations and accounting for the accuracy of greyscale and EOTF tracking.

Luminance Accuracy

Let’s just explain the EOTF graphs a little further here before we consider the luminance accuracy of this screen further. In the left hand image above you have an EOTF graph tracking the PQ curve for HDR. Along the horizontal X-axis you have the greyscale from 0 (black), through different shades of grey which get progressively lighter, to 100 (white). The vertical Y-axis is the PQ value, but basically you can think of this a bit like luminance. As you move up the value the screen has a higher luminance. This graph is just a logarithmic conversion of what an actual luminance graph would look like, which is included on the right. You can see the same greyscale 0 > 100 along the bottom but the vertical Y-axis is now luminance measurements directly.

The problem with the luminance graph is that the line is very flat until about greyscale 20 when it then starts to rise on the curve, even though visually you can identify differences in the image for those darker grey shades. In fact small differences in dark shades are more discernible by the human eye than the same differences in lighter shades. The curved graph is harder to read and compare which is why it’s converted to the PQ EOTF graph typically instead. Both graphs are measuring the same thing, but they’re presenting the data in a different way. The EOTF graph on the left is easier to identify where there are errors in not only the lighter shades, but also in the darker shades.

One other thing to note it that you will see in both cases when the lines reach greyscale value 70 (light grey) the yellow target line flattens out completely which would mean that if this is followed exactly by the monitor, all those grey shades from 70 to 100 should actually have the same luminance, and would therefore look the same. Those lightest grey shades get clipped and lost and become white basically. This is how it’s defined in the HDR PQ standard but it is down to the display manufacturer to determine the “roll-off” point. Often you will see the luminance drop a little lower and more gradually level off rather than take such a sharp turn at greyscale 70. That can then help preserve lighter grey tonal values. This is especially useful in situations where the peak luminance of white is lower, like for instance on OLED screens where the APL is high.

Think of it this way – for small 1% APL you might have a full luminance range of 0 – 1000 nits to play with on an OLED monitor, and so clipping light grey shades above greyscale 70 isn’t a major problem as they will be very bright at that point (nearing 1000 nits) and it’s going to be very hard to tell them apart anyway. For a large 100% APL the screen might only be able to reach perhaps 250 nits peak white and now you have a much smaller 0 – 250 nits range to play with. The display manufacturer might choose to clip the grey shades later on by rolling off the luminance more gradually since it’s going to be easier to tell the differences between those lighter grey shades when white is reaching only a much lower 250 nits peak.

To consider the “luminance accuracy” further of the HDR mode we need to consider the EOTF and luminance performance at a range of different APL’s. Our recent investigation of OLED HDR brightness has revealed that we can’t just rely on a single 10% APL measurement any more.

As well as providing some EOTF graphs at a few different APL’s beyond just the typical 10% APL measurement, we’ve been working on a useful way to measure and represent what we are going to call the “luminance accuracy” of the HDR modes. The tables above are a simple approach which tracks the luminance error. Each grey shade being measured is shown across the top of the table starting from 0 for black, and going through the grey shades until you reach 100 for white. Measurements are taken at a range of different APLs shown down the left hand side, from 1% up to 100% and the measured luminance of each grey shade is compared with the target it should be reaching.

The difference in luminance, whether that’s a positive number where it’s brighter than intended, or a negative number where it’s darker than intended is then captured in the table and colour coordinated. The blue areas are where the luminance is higher, and the pink areas are where it is lower. Ideally for a fully accurate greyscale performance all these squares would be white, which would reflect the ability to achieve the intended luminance for all the different grey shades, and at all the different APL areas. Having said that, as we said earlier it is quite common to have a gentler roll-off for luminance on the higher APL situations, as the absolute peak luminance that can be reached is much lower than at small APL levels, and rolling off a bit earlier helps preserve some light grey details. As a result, some pink-coloured error for larger APL’s in the mid to light grey shades is perfectly acceptable.

You can see from this table and the provided PQ graphs that the luminance is too high for mid to light grey shades, especially with the smallest APL window sizes being measured. In some cases the grey shade is up to 339 nits higher than it should be! This means that you can get crushing of light grey detail in all situations, especially where the overall APL is lower and the screen reaches its brightest highlights. On the other hand it does help provide a brighter and more impactful HDR image which some people may prefer, especially if you’re using your screen in a brighter room, during the day time, or just generally away from a reference dark environment. We would have preferred a more accurate setup here though. Near black the PQ graphs show that the luminance is a bit lower than intended, which causes the crushing of some near-black shadow detail. We’re talking minor numbers < 1 nit which is why they don’t show up in the table, but the graphs show the issue well.

There’s all kinds of other problems with the HDR image (far too cool colour temp, dimmer than necessary for brighter scenes/high APL) and so it’s just another issue really with the HDR setup here.

Another good way to represent the luminance is on the above graphs. Here we have considered an average of the measurements across the mid to light grey shades between values 45 and 75, and you can see a visual representation of which shades that covers with the gradient bar under the table on the left. This basically excludes the much darker shades, and also those that are near white, and often where clipping then occurs on OLED screens since they can’t get anywhere near the 10,000 nits upper limited defined for the PQ EOTF. These grey shades from 45 – 75 are the interesting area in terms of where problems arise in real-world brightness, and which will make up a significant portion of any brighter real-world HDR content areas.

On the graph itself the dotted grey line shows the average target luminance that should be reached for those grey shades, while the pale blue line tracks the average measured luminance. Ideally these lines would match if there was no error in the luminance and it was completely accurate. You can see here that the achieved luminance for grey shades is higher than intended for all APL % areas, and this reaffirms what is shown in the pink/blue tables earlier. The luminance for grey shades is higher than it should be, especially for smaller APL scenes.

Colour Accuracy

We can also consider the colour accuracy as measured above. You can see that overall the colour accuracy is poor in HDR, impacted largely by the overly cool colour temp which makes everything bluer and cooler than it should be. We had a dE average of 4.3 in our measurements.

Conclusion

Throughout our testing of the GZ2711 it felt like we were reviewing an unfinished product to be honest. We first received this screen a few months ago and when our first phase of testing uncovered some glaring problems, we fed back those initial findings and concerns to Cooler Master. A second unit was sent out which we were told was definitely a finished mass production sample, but unfortunately the same issues seem to be present.

Let’s touch on the positives first of all though shall we? From a gaming point of view the 240Hz OLED panel provides excellent response times, motion clarity and gaming experience. It has a very low input lag and the panel offers deep blacks and a high contrast ratio. It’s as we expected from a 240Hz OLED panel having reviewed many of these now. We liked the inclusion of some modern features and extras, including a USB-C port, which has a high power delivery too. The design is quite subtle compared with some gamer-aesthetic alternatives out there which looks sleek, and the stand was versatile and sturdy. Unfortunately, that’s largely where the positives stop.

In all the modes the gamma was really poorly configured. This was the situation in the native mode, as well as the provided sRGB, Adobe and DCi-P3 modes. The colour temperature was better at least, but we had really poor colour accuracy in all modes. Even the supposedly factory-calibrated sRGB mode was terrible in this regard, with poor colour accuracy, gamma and even a significant over-clamping of the intended colour space. That happens on the other emulation modes too.

The trend continues in to the HDR mode as well which was far too cool (with no colour temp settings to change it!), had poor PQ tracking and some oddities with the luminance accuracy as well. It’s almost as if Cooler Master have forgotten to configure any of the SDR or HDR modes. Even professional calibration devices couldn’t save the accuracy fully, it really was a mess.

Then there’s some other things which are missing or have been poorly thought through. There’s no uniform brightness mode available in SDR, which means you always get ABL dimming, which is annoying for desktop applications. There’s no reason that couldn’t have been included, and we can only put this down to a manufacturing oversight really. Console support was decent enough if you want to use a PS5, but the lack of Virtual 4K support was another glaring gap and means you simply can’t use HDR from an Xbox – even if you wanted to live with the poor accuracy and setup! Other user experience niggles like the fact that the brightness setting is the same for both SDR and HDR modes are a real pain too.

Where to Buy

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The GZ2711 is available at the moment at ~$750 USD in the US from Newegg and Amazon, or ~£600 GBP in the UK from Amazon and Overclockers. Given all the problems we cannot recommend this screen at all in its current state. We eagerly await some feedback from Cooler Master on this review, and perhaps this is something they can fix and which we can revisit later on. Right now, we can only review the screen as we’ve received it (2 separate samples) and unfortunately we can only conclude that Cooler Master’s entrance in to the OLED monitor market has been a bit of a disaster. If you’re looking for a new OLED screen we’d suggest checking out our current recommendations in each size segment here.

Pros	Cons
Excellent response times and motion clarity from 240Hz OLED panel	Terrible setup and configuration in all modes
Some nice extra features like USB-C	HDR accuracy is poor, and operation is annoying
Low input lag for gaming	Console support lacking Virtual 4K leaves gaps for Xbox HDR

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