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Noise

This time we’ve dedicated a separate section to the noise characteristics of tested graphics cards because we are now going to evaluate them not subjectively but with a digital sound-level meter Velleman DVM1326. This instrument has a resolution of 0.1dB and allows measuring in a range up to 130dB with A or C weighting.

What do these A and C mean? The fact is the human hearing is a complex non-linear psycho-physiological process. Sounds that have the same sound intensity but different frequency are perceived by the human ear as differing in loudness. Particularly, medium-frequency sounds are perceived as being louder than low- or high-frequency ones. As a result of scientific research in the 1930s, the equal loudness contours were produced (the so-called Fletcher-Munson curves). These curves show the sound intensity of different-frequency tones that are perceived by us as having the same loudness.

Three such contours, for sound intensity levels of 40, 70 and 100dB, were used to create A-, B- and C-weighting curves which help describe loudness with a single value that accounts for the way the human ear perceives sound. Currently, the A curve with a decline in 20-1000Hz range is an industry standard; the C curve with an almost linear frequency characteristic is used but seldom. The B curve is not used at all and is not even supported by our sound-level meter. Of course, we used the A curve for our measurements, so the results are shown in dBA.

The decibel is a logarithmic rather than linear measurement unit. It means that an increase in sound intensity by 3dB is the same as a doubling of intensity, but due to the non-linear nature of human hearing, it is commonly assumed that the perception of a twofold increase of sound loudness corresponds to an increase of sound intensity by 10dB.

We don’t have a special acoustic chamber, so the numbers we get in our test will differ from what the manufacturer specifies, yet they will be closer to real conditions the PC is used under. The level of background noise in our test room was 36dBA. At a distance of 1 meter from the working testbed with a passively cooled graphics card our sound-level meter showed 40dBA. We’ll base our judgments upon these two reference numbers.

We measured the level of noise produced by the cards in three modes: 2D, 3D typical and 3D maximum (the maximum level of noise with the automatic fan-speed adjustment). The noise is measured at a distance of 1m and 5cm from the working testbed assembled in a Chieftec LBX-01 system case with the side panel removed. Here are the results:

The diagram shows that Gigabyte’s cards produce about the same amount of noise in 2D and 3D modes and are equally quiet. It’s only when the fan of the Gigabyte Radeon X1900 XTX begins to rotate at a higher speed, reacting to an increase in the temperature of the GPU, that the difference becomes noticeable – 2.4dBA. This is not little considering the decibel is a logarithmic measurement unit. These results also comply with what you can hear with your own ears: when working at an increased speed, the cooler of the Radeon stands out among the other components of the system with its irritating “plastic-colored” noise due to resonance in the air-directing casing. The Gigabyte GeForce 7900 GTX is almost imperceptible by the ear under the same conditions, and you won’t hear it at all if your system case is closed.

At a distance of 5cm the Gigabyte GeForce 7900 GTX is quieter than the Gigabyte Radeon X1900 XTX, too. This is expectable, considering its 80mm fan rotates at only 1000rpm. Subjectively, a soft whispering of the air can only be heard. The Gigabyte Radeon X1900 XTX again produces that irritating “plastic” rumble with its blower and resonating casing. You may find it uncomfortable to be near this card when the fan speed management system decides to increase its speed. Fortunately, this is a hypothetic situation as no one is going to remain so close to the system case for long. This test however shows that the acoustic characteristics of the GeForce 7900 GTX cooler are better than those of the Radeon X1900 XT/XTX cooler.

So, in the most typical situation, when the PC is about 1 meter away from the user, the level of noise produced by Gigabyte GeForce 7900 GTX is 4.6dBA higher than that produced by the same system but with a passively cooled graphics card inside. This value remains constant in all the work modes of the graphics card and, thanks to its spectrum, is almost imperceptible against the noise from other system components (CPU cooler, hard drive, etc).

The Gigabyte Radeon X1900 XTX has worse results when running 3D applications for long. Its noise is 7dBA louder than the noise from the same system but with a passively cooled graphics card – that was perceptible by the ear. Fortunately, the fan of the Gigabyte Radeon X1900 XTX is not always working at its highest speed. Moreover, most games have internal sounds that override the graphics card’s noise.

 
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