Like zepper pointed out, this is more or less subjective trash.
Seeing that the directron silencer came 2nd in a fan review is enough for me to discredit it entirely.
"If a case fan comes with a fan speed control, the control is set at the lowest level allowing the slowest fan operation."
I see their logic in this. If a customer wants the quietest fan possible without considering any other information on fans, this would help.
But even then these undervolted fans should not be compared to fans at normal voltage without a HUGE disclaimer saying that this is not a fair comparison. If a customer is going to base purchasing off a subjective fan review, it is unlikely they going to read through the methodology and understand how flawed the review is.
You can 5V any fan. You can buy a rheostat/fanmate.
And I do not for one second believe that a panaflo L1a is nearly twice as loud as a vantec stealth at stock voltage.
For this to be a credible fan review 3 things would have to happen:
1. Use professional equipment ("This low-cost meter may not be the most accurate noise meter on the market; however for such a comparative study, it served our purpose just fine.") Their rating is +/- 1.5 DB.
2. Rate fans against each other where the only variable is the fan being tested.
3. Not host the fan review on a business webpage where there is potential (or evidence of) bias.