When graphics cards produce a lot of heat, usually that heat 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.
TYPICAL SOUND LEVELS
Jet takeoff (200 feet)
Shout (5 feet)
Heavy truck (50 feet)
Normal conversation (3 feet)
Bedroom at night
For each DBa test we close the PC/chassis and move the DBa gun 75 cm away from the PC. Roughly the same proximity you'll have a PC in a real-world situation.
We deliberately put the cards close together in the system, as most of the motherboards currently in use will need to be configured that way. This means that the upper graphics card will get way less airflow. The one somewhat airflow blocked card heats up quickly, producing more noise.
In CFX mode we got pretty bad DBa levels returned once the GPUs really start to stress, on average the noise level was 44 DBa, however when the two GPUs really have a card time then things get worse fast. In the Crysis WarHead benchmarks for example the cards spun up fast and reached 49 DBa of sound pressure, that's just downright noisy.
We'd recommend (if possible) leaving and extra slot in-between the two cards and create good airflow. At that stage even at hefty gaming noise levels will remain acceptable.
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