Now for the moment of truth. 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. Remember, out of necessity, we're using different motherboards for the CrossFire systems. Otherwise, the system components other than the video cards were kept the same.
The idle measurements were taken at the Windows desktop. The cards were tested under load running Oblivion using the game's Ultra Quality setting at 1600x1200 resolution with 16X anisotropic filtering.
Noise levels and cooling
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 14" from the test system at a height even with the top of the video card. The meter was aimed at the very center of the test systems' motherboards, so that no airflow from the CPU or video card coolers passed directly over the meter's microphone. 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 CPU and chipset fans. We had temperature-based fan speed controls enabled on the motherboard, just as we would in a working system. We think that's a fair method of measuring, since (to give one example) running a pair of cards in SLI may cause the motherboard's coolers to work harder. The motherboard we used for all single-card and SLI configurations was the Asus P5N32-SLI SE Deluxe, which on our open test bench required an auxiliary chipset cooler. The Asus P5W DH Deluxe motherboard we used for CrossFire testing didn't require a chipset cooler, so those systems were inherently a little bit quieter. In all cases, we used a Zalman CNPS9500 LED 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 cards' 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.
We measured the coolers at idle on the Windows desktop and under load while playing back our Quake 4 nettimedemo. The cards were given plenty of opportunity to heat up while playing back the demo multiple times. Still, in some cases, the coolers did not ramp up to their very highest speeds under load. The Radeon X1800 GTO and Radeon X1900 cards, for instance, could have been louder had they needed to crank up their blowers to top speed. Fortunately, that wasn't necessary in this case, even after running a game for an extended period of time.
You'll see two sets of numbers for the GeForce 7950 GT below, one for the XFX cards with their passive cooling and another for the BFG Tech cards, which use the stock Nvidia active cooler. I measured them both for an obvious reason: they were bound to produce very different results.