Output Noise
I use a Class 1
Bruel & Kjaer 2250-L G4 sound analyzer equipped with a Type 4955a microphone that features a dBA-weighted dynamic range of below 6 dBA and up to 110 dBA. All tests are conducted inside a hemi-anechoic chamber at 25–28 °C ambient, and the test subject is placed a meter from the sound analyzer.
The fan is not noisy at low speed, but starts to get noticeable at medium speed; you will surely hear it even if you are far away from the NAS at high speed.
Output Noise Comparison Graphs
The following graphs show the output noise of the AS3304T and compare it to other units I have tested.