Archive: SPCR's Unique Heatsink Testing Methodology

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* Revised January 15, 2007 by Devon Cooke
* Originally published October 23, 2002 by Mike Chin

Heatsink / Fans (HSF) or coolers for CPUs are bread and butter at most hardware sites. The market for aftermarket heatsinks has exploded since the introduction of the AMD Athlon processor — in its day the hottest processor ever sold and the first to require more than 50W. Fast forward to 2007, and the number of HSF on the market must have reached the thousands, and some of the latest processors now consume more than double the power of the original Athlon. Heatsinks are big business: Look around on the web on any given day, and you see a handful of new reviews of yet more HSF. So what can we contribute?

The CPU cooler is one of the five major sources of noise in a typical PC — the others being the power supply, system fans, video cooler, and the hard drive. Unlike most hardware sites, we are not interested in reviewing all of them. No, we are interested only in coolers that do their job quietly, or can be made to do so quietly. We select coolers for review on the basis of these questions:

  • Is it considered so good that we just have to see how it does with a quiet fan?
  • Does it look like it can be run quietly (even though it is not designed or marketed as quiet)?
  • Does someone we know and have reason to trust say it's quiet and good?
  • Is it marketed or designed as a quiet heatsink? (Most heatsinks these days are...)
  • Can a sample be readily obtained?

Testing Heatsinks vs. Testing Fans

SPCR has been testing heatsinks for almost five years. Our test bed has evolved through several generations as times have changed as CPU sockets and mounting systems have come and gone. But, no matter what the underlying technology, SPCR's testing has always had a slightly different emphasis than the testing done by other web sites.

CPU heatsinks are usually packaged and marketed with a fan, which explains the rise of the moniker HSF, heatsink fan. Most hardware web sites test the HSF as an integrated unit. For SPCR, this is not an ideal way to do things, mainly because almost all fans supplied with HS are too loud. That's not to say there aren't exceptions — we can think of one or two models that are quiet in stock form — but these are not yet the norm. At the very least, most HSF units require a way of reducing fan speed to be made quiet, and all too few include a means of doing this out of the box.

Because of this, we don't ask the questions that others do:

How much cooling achieved with this HSF?

Instead, we ask,

What is the cooling power of this heatsink with this quiet fan whose characteristics are well known?

By asking this question, we put all the heatsinks on the same playing field — no screaming 100 CFM fans. All have only the aid of the same low noise, low airflow fan. We remove the cooling advantage of powerful noisy fans, which is a cheap, brute-force method of cooling. The heatsink, then, is the only variable.

The benefit of this approach is that it guarantees that all heatsinks are tested under the same acoustic conditions. What we want to know is how well a heatsink performs at a given (quiet) noise level, and using the same fan for all our tests gives us a way of reproducing the same noise level every time we do a test.

That being the case, we are well aware that most people are not inclined to purchase both a heatsink and a fan, so we actually run two tests for every review: One with our reference fan, and one with the heatsink in stock form. When that exceptional heatsink that ships with a quiet fan appears, don't worry, you'll know about it. Stock fans are profiled according to our standard fan testing methodology, which uses a similar noise-centric approach.

We consider the heatsink and mounting mechanism together as a unit. A heatsink's intrinsic cooling power is determined mainly by:

  • its radiating surface area
  • the heat transfer coefficient of its materials
  • the spacing and number of fins
  • its geometry
  • the smoothness and flatness of the CPU contact surface
  • overall mass
  • ease and efficacy of the mounting mechanism

The mounting mechanism is mentioned because it maintains the all-important contact between CPU and heatsink. The amount of pressure brought to bear on the interface also affects cooling. It is also the only real interface between HS and user.

We may say we use a HS, but it's not the same way that we use a car, for example. We interact constantly with a car while using it. If there is any aspect of user interaction with a HS, it really happens only when the HS is installed or uninstalled. If this design aspect is poor and results in the user having difficulty with installation, or failing to mount the HS correctly, then poor cooling performance leading to shutdown or downright failure of the CPU can result. Some mounting mechanisms are poor, both difficult to install and lacking in precision or security; others are integrated wonderfully into the heatsink and easy to use.

Our point of view is that the mounting mechanism is a critical part of the HS design. Lack of attention to this detail suggests a design that is not completely thought through.

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