Just to add to this, cut of grill and fan positioning in proximity to the grill has made a big difference in some of the chassis I've worked on. In a couple 5mm aluminum chassis we had stamped with a honeycomb for the grill, we noticed a significant difference in noise when we had the fans planted up against the grill compared to ducted at 1cm or more. I don't believe it was from chassis vibration, as this was pretty thick metal. Different fans seem to react more severely to restrictive situations. This specific situation was in an open top and rear rack mount case, the volume changed once it was sealed and assembly completed of course, but the point of interest lies in the grill. @Toka: The point I'm trying to make is, fans will be affected differently by their mounting environment, it's not necessary to make a chassis mount test per-se, but a least bolt a plate inhibiting airflow to reference the affected numbers. It is important that these articles remain relevant. I send charts like this sometimes over to the idiot sales team so they have some idea as to what they're doing when a customer asks for upgraded fans.