360° View - Noctua NH-D9DXi4-3U Heatsink Information on Frostytech's test methodology is available here.
The NH-D9DXi4-3U heatsink stands 111mm tall and is equipped with one 92x92x25mm NF-A9 PWM fan that spins at 2000RPM. Power is supplied by a standard 4-pin motherboard header. A second fan can be attached (user supplied), increasing the NH-D9DXi4-3U's overall length to 122mm. The nickel plated aluminum fins measure 0.4m thick and are spaced 1.75mm apart. Heatpipes are spaced roughly 18mm on center.
The NH-D9DXi4-3U utilizes two 67mm tall stacks of nickel plated aluminum fins, soldered to each of the four 6mm diameter copper heat pipes. The bottom cooling fin is elevated 35mm above the motherboard for clearance. The copper heat spreader measures 2-5mm thick. The fan is held in place by wire fan clips with low-profile thumb tabs to make insertion/removal easy.
The nickel plated copper heatspreader at the base of the Noctua NH-D9DXi4-3U heatsink is soldered to all four heatpipes for lower thermal joint resistance. The base has a machined surface finish and the contact pad measures 38x40mm. Looking at the top of the heatsink we can see that each aluminum fin is 95 x 34mm in size and features small hole at each corner for the supplied allen key to pass through so that the spring tensioned mounting screws may be tightened.

Base Finish and Flatness

Flipping a heatsink over to inspect the business end is often a simple indicator of overall cooler quality. More practically speaking, a heatsink is in many ways only as effective as the contact it makes with the processor - the flatter and smoother the better. Base finish is one of the criteria that Frostytech measure in the course of evaluating heatsinks, and it involves two distinct aspects. Surface Finish is the first; this is calculated with the aid of Surface Roughness Comparator that has a cross section of common machine surface finishes and their numerical surface roughness equivalents in microinches. The second is Surface Flatness. This is tested with an engineer's straight edge or proven flat surface, in two axes.

The Noctua NH-D9DXi4-3U heatsink uses a nickel-plated copper base plate which is machined very smooth, surface roughness is at or better than ~8 microinches. The base is very slightly concave in the axis parallel to the heatpipes and very slightly convex in the opposite axis.

Sound level measurements are coming up next on Frostytech...