The Big Reveal: Power And Noise
Sitting on the Windows desktop, the dual-GPU Radeon HD 6990 impresses us. It uses less power than a single-GPU GeForce GTX 480 and less than the Radeon HD 5970 2 GB. It takes Nvidia’s reworked GeForce GTX 580 to show us more conservative idle power figures.
The situation changes in a big way when you apply a load. We’re not even talking about maximum power figures here. I’m simply logging three iterations of the built-in Metro 2033 benchmark—something you’d see during everyday game play, rather than a “power bug” like FurMark. On average, the Radeon HD 6990 running with its overclocked BIOS uses 94 W more than a GeForce GTX 480. And the GTX 480 already gets ridiculed for its power consumption!
We’ve seen some elegant high-performance graphics cards from AMD, but this is not one of them. It brute-forces performance like a broadsword through cloth.
So, what does it take to dissipate the heat generated by a 375 W card?
Apparently, it takes a noise chart uglier than sin itself.
The problem is that AMD doesn’t use a graceful ramp. It instead steps fan speed up and down to address thermal demands. As a result, you hear the board’s cooler accelerating and decelerating like an engine when the driver downshifts coming up to a stop light.
This is something Nvidia put a lot of thought into after getting skewered for the GeForce GTX 480. I dissected a GPU-Z log file taken while just sitting on the Just Cause 2 menu screen and came up with the following:
Up to about 78 degrees Celsius, the Radeon HD 6990's fan spins at about 2180 RPM. We’ll call that the safe zone. Within a minute or so in a 3D application, the warmest GPU heats up to somewhere between 88 and 89 degrees, and the fan cranks up to 2880 RPM. That’s “who played a trick on me and swapped my graphics card out for a GeForce GTX 480?” territory. Both the AMD and Nvidia cards crank out about 51 dB. In order to keep the card at 90 degrees or less, the fan then speeds up to 3600 RPM, or what I call Charlie Sheen F-18 mode.
There’s no excuse for a graphics card to be this loud and, if spinning its cooling fan up to 3600 RPM is the only way to keep the Radeon HD 6990 from overheating, then this product simply isn’t ready for consumption. Because the problem is related to fan speed, there’s a chance an updated firmware could smooth out the way AMD handles heat. Right now, though, there’s no way I’d install one of these things in a gaming machine.
The problem is compounded by the fact that two Radeon HD 6970s in CrossFire top out at 53.1 dB(A) (slightly louder than a single GeForce GTX 480) and two GeForce GTX 570s in SLI max out at 49.1 dB(A)—quieter than a Radeon HD 5970. Both card combinations exhaust all of their air out the back of your chassis, they’re both quieter, and the 6970s, at least, are universally faster.
