Cooling Noise and Power

For my last few tests, rather than focusing on in game performance, I like to check out other aspects of video card performance. These are also the most important ways to differentiate the performance between cards that have the same GPU. To start things off I took a look at power usage. For this, I use our Kill-A-Watt hooked up to the test bench to record the total wattage of the system. I ran two tests with the first using 3DMark Time Spy to put the system under a load similar to normal in game performance. Here our test system with the MERC 310 7900 XT  pulled 576 watts which was just behind the 7900 XTX and up over even the overclocked RTX 4080. I also ran AIDA64’s stress test on the video card to load up only the GPU and using the Kill-A-Watt the test bench with the MERC 310 7900 XT pulled 488 watts and is sitting between the RTX 3080 and the RTX 3080 Ti.

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While the overall system numbers are nice, with the addition of a PCat into our testing hardware I have finally been able to look at the total power draw of just the GPU by monitoring the power over the PCIe slot and the power cables. For this test I have also expanded the number of tests I run by testing power usage in two games (Fay Cry 6 and Watch Dog Legion both at 4k and ultra detail) testing with Time Spy and Time Spy Extreme, AIDA64’s GPU workload, and Blender 3.4. I take those numbers and average them out for our average number and also look at the max wattage which is with just one exception always the Time Spy Extreme result. This gives us a much better look at the power usage across multiple situations and also the max power draw. The MERC 310 7900 XT pulled an average of 385 watts which put it up over the overclocked XFX 6800 XT and is 35 watts more than the stock 7900 XT. This also puts it up near the stock-clocked 7900 XTX. For peak wattage, the MERC 310 7900 XT is just 1 watt away from the 7900 XT.

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My next round of tests were looking at noise levels. These are especially important to me because I can’t stand to listen to my PC whirling. Especially when I’m not in game and other applications are using the GPU. For my testing, though I first tested with the fan cranked up to 100% to get an idea of how loud it can get, then again at 50% to get an idea of its range. I test using both A and C weighting, A is the standard way and C has a little more of the low end to check for low-level hums. The MERC 310 7900 XT wasn’t exactly quiet for the 50% fan speed test, landing near the top of our charts at 49.3 decibels. The 100% fan speed test was similar with the MERC 310 7900 XT  again up near the top of the charts at 65.7 decibels which is surprising with the MERC 310 7900 XT fan RPM being down below the middle of the chart. I also take a look at noise performance while under load. For that when running AIDA64’s stress test I wait until the temperature of the card has leveled off and then measure how loud things are when the card is at its worst-case scenario with the stock fan profile. Here the MERC 310 7900 XT came in at 42.9 decibels which is again up at the top of our chart but was quieter than the stock 7900 XT in the same test.

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To finish up my testing I of course had to check out the cooling performance. To do this I ran two different tests. I used AIDA64’s Stress Test run for a half-hour each to warm things up. Then I documented what temperature the GPU leveled out at with the stock fan profile and then again with the fans cranked up to 100%. With the stock profile, the MERC 310 7900 XT did extremely well coming in at 54c, 7 degrees less than the stock 7900 XT. Then with the fans cranked up, the MERC 310 7900 XT cooled things down further to 47c which was just 1 degree below the reference 7900 XT. Of course, given the higher power usage and the overclock the MERC 310 7900 XT is doing very well to deal with the additional heat. The delta between the two was 7c, which isn’t leaving too much headroom left in the cooler but the MERC 310 7900 XT is already overclocked with an aggressive overclock from XFX.

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While running the stock fan profile testing I also took the time to get a few thermal images so we could see what is going on. As expected with the heatsink designed to push air out the top and bottom of the card the hotspot is up on the top edge of the card, even when facing the fan side. That said the top thermals are cooler than the stock 7900 XT and the fan side is especially cool with parts down to 25c. The top-down view shows the hottest area is the vapor chamber that sits over the GPU and memory and helps spread the heat out across the heatsink. The top venting airflow does also have the power cables warmed up somewhat as well but not enough to be a concern. Then the backplate view shows that most of the heat is centered behind the GPU and the thick aluminum backplate is doing a great job of dissipating heat out using the groves in the backplate as an additional heatsink. 

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