I'm arriving a little late at the party, I guess...
I suppose an extrapolated conclusion (as drawn by me as well as several other readers) is that a very good budget solution is to add asecond fan of the original variety...
PartEleven wrote:Does scythe sell that PWM slip stream fan separately?
Yes! (And you also need an extra set of clips, type "A".)
MikeC wrote:OK, to clarify the 2 fans vs 1 fan SPL measurements and perceived noise, I ran some extended tests ... All the tests were conducted in the anechoic chamber, whose ambient was reading ~11 dBA. ...
either fan at 1000 rpm: 14 dBA/1m
both fans at 1000 rpm: 18 dBA/1m
This makes sense, more or less. ...
either fan at 700 rpm: 11 dBA/1m -- 12 dBA/0.5m
both fans at 700 rpm: 12 dBA/1m -- 14 dBA/0.5m
The first reading above -- 11 dBA/1m for the single fan at 700rpm (which is roughly the same speed as 7V w/ the Nexus 120) -- is suspect. Why? It's the ambient level. This means the fan could be anywhere between 0 and 11 dBA/1m and there's no way to tell, because 11 dBA is the lowest we can measure.
I think there's a difference between what can be measured and what can be calculated.
I know from the screenshots that your equipment provide two decimals to the measured value, which adds quite a bit of precision.
To get a more accurate value of the fan noise it's just a matter of subtracting the background noise:
(Actual fan noise) = 10 x log( 10^(Measured fan noise)/10 - 10^(Measured background noise)/10 )
Example 1, both fans at 1000rpm.
Measured: 18.00 dB
Background: 11.00 dB.
Actual fan noise: 10 x log(10^1.8-10^1.1) = 10 x log(63.10-12.59) = 10 x 1.70 = 17.0 [dB]
Example 2, both fans at 700rpm (1m distance).
Measured: 12.00 dB
Background: 11.00 dB.
Actual fan noise: 10 x log(10^1.2-10^1.1) = 10 x log(15.85-12.59) = 10 x 0.51 = 5.1 [dB]
On top of these result one can then add the inaccuracy of the audiometer.
Cheers
Olle