Why 40 dB(A)?
First of all, note the A in the decibel notation. That stands for A-weighting. It means that sound pressure levels are adjusted using a curve that mimics human sensitivity to noise levels at different frequencies.
Forty decibels is generally considered to be the average background noise level for a commonly quiet apartment. Recording studios might be in the 30 dB range, while 50 dB might be a quiet suburb or a conversation at home. Zero is commonly considered the threshold of human hearing, although it's uncommon to hear in the 0-5 dB range unless you're less than five years old. The decibel scale is logarithmic, and not linear. So 50 dB is twice as loud as 40, which is twice as loud as 30.
Trivia: The world's quietest room has a -9 dB background noise level, and will reportedly give you hallucinations in less than an hour if you stand inside in the dark, due to sensory deprivation.
A PC operating at 40 dB(A) tends to blend in with the background noise level of your home/apartment. Generally, it shouldn't be noticeable.
How Do You Dial In 40 dB(A) Consistently?
A card's noise profile is affected by a few variables, one of which is the speed of its fan. Not all fans make the same amount of noise at the same RPM level, but each fan, on its own, should be consistent at a given rotational speed.
So, by measuring directly with a SPL meter from three feet away, I manually set each card's fan profile right at 40 dB(A).
|Card||Fan Setting %||Fan RPM||dB(A) ±0.5|
|Radeon R9 290X||41%||2160||40.0|
|GeForce GTX 690||61%||2160||40.0|
|GeForce GTX Titan||65%||2780||40.0|
The table above shows us that the Radeon R9 290X and GeForce GTX 690 achieve 40 dB(A) at the same fan speed, although at different fan settings. The Radeon's fan can be pushed higher overall, hitting rotational speeds and noise levels that the GTX 690's cooler cannot. Nvidia's GeForce GTX Titan, on the other hand, has a different noise profile, hitting 40 dB(A) at a higher 2780 RPM, but at a setting (65%) similar to the GeForce GTX 690 (61%).
This table illustrates fan profiles along a variety of presets. Overclocked cards under load can get pretty loud; I measured around 47 dB(A). The Titan is the quietest under a typical load, at 38.3 dB(A), while the GeForce GTX 690 is the loudest at 42.5 dB(A).
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