Power consumption
We measured total system power consumption at the wall socket using an Extech power analyzer model 380803. The monitor was plugged into a separate outlet, so its power draw was not part of our measurement. The cards were plugged into a motherboard on an open test bench.
The idle measurements were taken at the Windows Vista desktop with the Aero theme enabled. The cards were tested under load running UT3 at 2560x1600 resolution, using the same settings we did for performance testing.
Note that the GeForce 8800 GT SLI config was, by necessity, tested on a different motherboard, as noted on our Testing Methods page.
Personally, I think the X2's power consumption at idle is impressively low. Although it has two GPUs and two banks of 512MB of memory, our X2-based system draws only 12W more at idle than the GeForce GTS 512-based one. The 8800 Ultra-based system draws over 20W more. Under load, the situation changes, and the X2-based system draws quite a bit of power—more than the Ultra-based system and more than the 8800 GT SLI system, which is easily the better performer.
Notice, also, that the X2 doesn't quite live up to AMD's claims. It does draw a little more power than two Radeon HD 3870s in CrossFire, both at idle and under load.
Noise levels
We measured noise levels on our test systems, sitting on an open test bench, using an Extech model 407727 digital sound level meter. The meter was mounted on a tripod approximately 12" from the test system at a height even with the top of the video card. We used the OSHA-standard weighting and speed for these measurements.
You can think of these noise level measurements much like our system power consumption tests, because the entire systems' noise levels were measured, including the stock Intel cooler we used to cool the CPU. Of course, noise levels will vary greatly in the real world along with the acoustic properties of the PC enclosure used, whether the enclosure provides adequate cooling to avoid a card's highest fan speeds, placement of the enclosure in the room, and a whole range of other variables. These results should give a reasonably good picture of comparative fan noise, though.
Unfortunately—or, rather, quite fortunately—I wasn't able to reliably measure noise levels for any of these cards at idle. Our test systems keep getting quieter with the addition of new power supply units and new motherboards with passive cooling and the like, as do the video cards themselves. I decided this time around that our test rigs at idle are too close to the sensitivity floor for our sound level meter, so I only measured noise levels under load.
What you should take from these results is that, at least on our open test bench, the X2 was perceptibly louder than any of the other graphics solutions we tested. That's definitely what my ears told me. And yet, I really can't complain too much about the X2's noise levels. The cooler can be loud when the system is first powered on, but that's it. During normal gaming, like the scenario we tested here, the card really isn't very loud. It's at least not into the "annoying" range for me. We're talking loud-whisper level here.
GPU temperatures
Per your requests, I've added GPU temperature readings to our results. I captured these using AMD's Catalyst Control Center and Nvidia's nTune Monitor, so we're basically relying on the cards to report their temperatures properly. In the case of multi-GPU configs, well, I only got one number out of CCC. I used the higher of the two numbers from the Nvidia monitoring app. These temperatures were recorded while running UT3 in a window.
There you have 'em. Kind of an interesting complement to the noise and power numbers, I think. I could live with a little more noise and little less heat from the 8800 GT and the Radeon HD 3870s in CrossFire.
