How We Measure Noise
We measure each graphics card's noise levels with a calibrated high-quality studio microphone (supercardioid) 50 cm away from a position perpendicular to the middle of the board. This distance, as well as the strong cardioid microphone characteristic, represent a compromise between avoiding noise generated by the fan’s airflow and ambient noise that can never be completely eliminated. Our noise-dampening efforts certainly help minimize the latter, but they'll never be 100-percent successful.
This year, we also had to decide (yet again) if we should use sone, dB, or dB(A) for our charts.
Decibel or Sone?
The definition of perceived loudness expressed in sone is based on sound pressure. One sone equals 40 phon, which in turn is defined as a pure 1 kHz tone at 40 decibel (dB). Sone scales with perceived loudness (that is, a sound pressure perceived to be twice as loud as 1 sone has 2 sone, and a sound pressure perceived to be half as loud as 1 sone has 0.5 sone). At first glance, this appears to be a logical, practical, and easy way to express noise level. Unfortunately, a closer look at how it works in practice reveals some irritating problems.
An increase in loudness by 10 phon from a starting point of 40 phon, totaling of 50 phon, results in a perceived doubling, which makes it 2 sone. However, the situation isn't straightforward under 40 phon. In that range, a reduction of less than 10 phon is enough to halve perceived loudness. And typically, the sound pressure produced by graphics cards at idle (along with quiet products under partial load) is almost exclusively below the 40 dB (40 phon, 1 sone) limit. So, recording an idle board's noise level in sone is difficult and potentially confusing. Overall, sone is better-suited to expressing higher sound levels.
Complex Noise Instead of Pure Tones
Another problem with sone is that it’s based on and scales with the perception of loudness of a pure 1 kHz tone. As we know, a graphics card's fan doesn't generate a pure tone at all. Rather, it produces complex noise covering a spectrum of frequencies.
The debate gets even more complicated when you try to compare noise from a centrifugal fan to that of an axial fan, and crazier still when you take different diameters and speeds into account. A sone value is strongly dependent on a graphics card cooling solution's specific sound profile, making the loudness rating it provides hard to interpret, even though that's theoretically the most exact way of expressing it.
The Human Ear
Coming back the other way, acoustic measurements use weighted sound pressure levels to reasonably model the human ear’s sound perception, simplifying our conundrum a bit. This is achieved through the use of filters, which are based on weighting curves defined in the DIN EN 61672-1/-2 norms. These filters are designed to provide a similar frequency response to that of the human ear for loudness measurements.
When you get right down to it, these are still only estimates. But, depending on the quality of your measurement device, they should be more representative for the range below 40 dB than sone values. Of course, providing dB(A) values only makes sense if the distance to the source of the sound is given as well (we make sure to do this).
With all of this considered, we'll keep using dB(A) for our noise measurements. Based on your feedback, though, I also want to give you the following table as a frame of reference. Hopefully dB(A) reference ranges with my own commentary adds meaning to the quantitative data that comes from our readings.
|Audio Comparison Table|
|< 31 dB(A)||Very good cooling solutions at idlePassively-cooled graphics cards|
|31 - 33.9 dB(A)||Mediocre cooling solutions at idleGraphics cards with idle fan speed set too high (~40%)Entry-level graphics cards with very good cooling solutions under full load|
|34 - 35.9 dB(A)||Entry-level graphics cards with average cooling solutionsMid-level graphics cards with very good cooling solutions under full load|
|36 - 39.9 dB(A)||Mid-level graphics cards with good cooling solutions under full loadHigh-end graphics cards with very good cooling solutions|
|40 - 44.9 dB(A)||Mid-level graphics cards with below-par cooling solutionsHigh-end graphics cards with average cooling solutions|
|45 - 49.9 dB(A)||Generally loud graphics cards with below-par cooling solutions|
|> 50 dB(A)||Unbearably loud, usually graphics cards with reference coolers|