A polished surface - but the heat transfer is impaired by the ridges
NorthQ's cooler is somewhat louder than its rival from Zalman, presumably because of its corrugated plates. At the lowest speed, we measured a barely audible 33.4 dB(A); at the highest setting the noise level went up to 44.8 dB(A), and was somewhat annoying. Yet it's not too loud to work.
At full power the temperature of the Pentium 4 580 was 58° C; at the lowest speed the temperature was 65 °C, which doesn't cause the CPU to throttle, so the values are fine.
We calculated a thermal resistance of 0.27 K/W, which is good.
The NorthQ cooler sells for around $45. We would recommend it for users who use the Athlon XP processor but who want a cooler that will still be up-to-date in the future.