But then isn't it strange that the 3 TB Red is not much louder than the 2 TB Red according to the same Hardwareinfo review, neither in idle nor active mode? The 3 TB Red has 1 platter more than the 2 TB Red, but the noise level is almost the same.
and it should be remembered that Harwareinfo measures the noise from a 10cm distance. Such a short distance could lead to exaggeration of small differences when compared to measurements at 1m -- "The noise production test is done in a sound-proof cabinet at a distance of 10 cm
That's interesting! How many dB exaggeration could that measurement method result in? After all we're talking about 33-29.4=3.6 dB difference in active mode between the 4 TB Red vs 3 TB Red. Could the measurement method they used explain all of that?
In addition, if their measurement method results in such a severe margin of error, is it really valid to specify the noise level in tenths of a dB? Are their measurements accurate enough for that?
We'll see with our 4TB sample. We reviewed a 3TB & a 1TB Red -- http://www.silentpcreview.com/WD_Red
-- but not a 2TB. At 1m, the difference between idle/seek was essentially nonexistent, and the two drives were just about 1 dBA apart, the 3TB reading 12-13 dBA.
As for how much exaggeration hardware.info's method could produce, it's hard for me to say with any precision without actually seeing and playing with their setup. Definitely, at 10cm, there'd be bigger measured dB differences than at 1m! And you are totally right to question the validity of citing 1/10 dB readings -- even 1 dB is not obviously audible to a lot of people, and acoustic measurements less than 1 dB are difficult to obtain consistently (because of setup & background noise variations; even temperature & humidity can affect these things.) Our general rule of thumb for our own measurements is not to be concerned about noise differences of 1 dBA or less, especially when it's under 20 dBA -- below the background noise of most rooms.