Page 5 - Power consumption, PSU, Heat & Noise levels

Power consumption & PSU recommendation

It's time to do some actual testing with the card. We'll start off by showing you some tests we have done on overall power consumption of the PC. Power consumption is a big thing, and I'm thrilled to see what has been achieved here.

Looking at it from a performance versus wattage point of view, the power consumption is really good with the new 55nm products. Our test system is a Core 2 Duo X6800 Extreme Processor, the nForce 680i SLI mainboard, a passive water-cooling solution on the CPU, 2GB memory, DVD-ROM and WD Raptor drive. Have a look:

Observe closely the difference between the 2900 and the 3870 X2. Shocking as performance is now nearly double yet the wattage we measured is still a little lower. A big thumbs up to AMD here.

In my view the Radeon HD 3870 X2 series require you to have a 550+ Watt power supply unit at minimum if you use it in a high-end system, and I think that's barely on the safe side. Also recommended is 30 AMP's on the 12 volts rails for stable power distribution (on a single card configuration)

Notice that the card uses one 6-pin power connector and another 8-pin connector.

If you have dough to spend and opt the guru path of righteousness by doubling up towards two cards in your system -> CrossfireX, then you should end up with a 1000 Watt or better PSU with a 50 AMPs 12 Volts rail. Definitely check out this PSU review, please.

There are many good PSU's out there, please have a look at our many PSU reviews as we have loads of recommended PSU's for you to check out in there. What would happen if your PSU can't cope with the load?:

• bad 3D performance
• crashing games
• spontaneous reset or imminent shutdown of the PC
• freezes during gameplay
• PSU overload can cause it to break down

The HIS Radeon HD 3870 X2 thermal envelope

Let's have a look at the temperatures these cards produce. We measured at a room temperature of 21-22 Degrees C, look at idle temperature and then load the GPU 100% for a couple of minutes and measure the temperature once a second and follow the temperature delta.

Above you can can observe the thermal envelope during a quick stress test. The idle temps are short from astonishing. Expect 50 Degrees C idle temps. The the load temperature on the GPUs was not bad, it rose towards 79 Degrees C. Which for a card with two active GPU cores is not bad at all.

BTW - if you look at the graph and focus on Core Clock MHz, you can see ATI PowerPlay at work. The second of the two GPUs is not fully utilized nor on 2D mode, the card will clock down, keeping it cooler and preserving energy consumption. So that's a very dynamic process.

The cooler is massive and industrial though. ATI locked it at a low FAN rotation which is inaudible. If you can life with a little bit of noise, you could tweak the RPM yourself and get the temperatures down even further.

Noise Levels coming from the graphics card

When graphics cards produce a lot of heat, that heat usually needs to be transported away from the hot core as fast as possible. Often you'll see massive active fan solutions that can indeed get rid of the heat, yet all the fans these days make the PC a noisy son of a gun. I'm doing a little try-out today with noise monitoring, so basically the test we do is extremely subjective. We bought a certified dBA meter and will start measuring how many dBA originate from the PC. Why is this subjective, you ask? Well, there is always noise in the background, from the streets, from the HD, PSU fan etc etc, so this is by a mile or two not a precise measurement. You could only achieve objective measurement in a sound test chamber.

The human hearing system has different sensitivities at different frequencies. This means that the perception of noise is not at all equal at every frequency. Noise with significant measured levels (in dB) at high or low frequencies will not be as annoying as it would be when its energy is concentrated in the middle frequencies. In other words, the measured noise levels in dB will not reflect the actual human perception of the loudness of the noise. That's why we measure the dBa level. A specific circuit is added to the sound level meter to correct its reading in regard to this concept. This reading is the noise level in dBA. The letter A is added to indicate the correction that was made in the measurement. Frequencies below 1kHz and above 6kHz are attenuated, where as frequencies between 1kHz and 6kHz are amplified by the A weighting.

We start up a benchmark and leave it running for a while. The fan rotational speed remains constant. We take the dBA meter, move away 75 CM and then aim the device at the active fan on the graphics card.

In idle the card does not make a lot of noise at all, you have to close in on the system to be able to hear it. We measured the PC at 40 dBa which is really good.

Once you get to play games and stress the card, the ventilator RPM will kick in at a high level. You will then hear the fan and dBa levels will hover at roughly 45 dBa, which is still quite normal.

So overall I'm happy with the noise levels of the product.