Review: Thermalright SP94, SP97 & other heavyweights

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The SP94 and SP97 clearly deserve the top rank on Thermalright's product lineup. They are clearly better performers than the earlier SLK900, and the advantage will show up especially with hotter CPUs. In many ways, the performance of the Thermalright heatpipe heatsinks is limited by the exclusive use of the Panaflo 80L in this review. A quiet 92mm fan such as the Panaflo 92L may be the best compromise for these heatsinks, which are probably best used with the hottest CPUs. With the increased airflow from Panaflo 92L, I would expect both SP94 and SP97 to equal or exceed the performance of the Zalman 7000s at the latter's 5V (~20 dBA) noise level. Even with the lower airflow Panaflo 80L, the Thermalrights come very close to matching the Zalmans.



* Great basic design
* Extremely secure bolt-thorough mounting
* Very high cooling performance
* Flexible fan options, including a 92x38mm fan
* High weight
* Cost?
* Complex installation

For those who like their heatsinks and fans served a la carte, there is probably no higher performance choice than the SP94 or SP97.

* * *

Great thanks to Thermalright and Silicon Valley Compucycle (SVC) for the Thermalright heatsink samples, and to Sharka Corp for the Zalman samples.

* * *

An Aside: SP94's Trouble with Heatspreaders

The SP97 vs SLK900U and the SP94 vs SLK900U comparisons are really interesting. The SP97 on the XP2500+ enjoys a big 4~5°C cooling performance margin with the Panaflo fan at 12~9V, and the advantage remains at 2°C down to 7V. These numbers are quite a contrast to the SP94, which shows barely any cooling advantage over the SLK900U on the P4-2.8.

Now it's very clear that the SP94 and SP97 are essentially twins. They differ only in the interface hardware to mount them to different CPU platforms. It seems logical to think that they would have a similar advantage over the SLK900U on either platform. (Each of these four measurements were done 3 times, by the way, with the same results.)

So what is the difference? The difference appears to be in the CPU itself. Not in the power dissipation, which is purportedly within a couple percent of each other (a watt or two), but in the presence of the heat spreader in the P4-2.8 and the absence of one on the XP2500+.

It has been discussed in the pages of SilentPCReview that Intel's integrated heat spreader (IHS) has the primary functions of

  1. physically protecting the CPU core from damage while heatsinks are installed or removed, and
  2. to reduce localized hot spots on the die

Given the number of reports of cracked AMD K7 and XP core in the last few years, this was probably a very smart marketing move by Intel. AMD has finally followed suit this year, integrating a heatspreader on their 64-bit CPUs.

One side effect of the IHS is to actually increase the overall thermal resistance of the CPU. (Please see the comment entitled UPDATE on Integrated Heat Spreaders! in the article CPUs Ranked by Noise / Heat.) This effect occurs because the IHS introduces 2 additional thermal layers: The IHS itself and the interface between the inside of the IHS and the core. According to one intrepid modder who removed the IHS, a large gob of ordinary thermal interface material (TIM), probably silicone, is used under the IHS. So instead of a single TIM layer between heatsink base and CPU core, there are 2 TIM layers, with a piece of not-that-smooth or flat copper in between.

My hypothesis, then, is that the IHS on the test platform P4-2.8 increases thermal resistance enough to render meaningless the performance difference between the SP94 and the SLK900. Because the XP2500+ does not have a heat spreader, the cooling difference between the SP97 and SLK900 is clearly seen. The SP97/SLK900 comparison suggests strongly that the SP94 is similarly better than the SLK900, even though the advantage is not seen here.

There are probably two circumstances in which the cooling performance gain of the SP94 could be seen:

  1. In hotter conditions, particular with a hotter CPU.
  2. On a CPU without an IHS.

Yet Another Aside: Z7000alcu at 4V

We've deliberately limited the low voltage testing of fans to 5V, simply because it is the lowest practical voltage that's easily available in a PC. Most fan controllers also don't provide lower than 5V, partly because that's about the lowest voltage at which most 12V fan will reliably start. Zalman fan controllers all provide 5V min.

But as this review was being wrapped up, it occurred to me that I do have a simple way of trying the Zalman 7000 HSF at lower than 5V. The Sunbeam Rheobus Fan Controller reviewed here last year, actually goes from 0V to 12V output in a continuous range. It got dug out from under the clutter of the test lab and hooked up into place. The only way to know how much voltage is going to a fan is to actually measure across the terminals, which is what I did. At 4V, these are the excellent results with the Zalman 7000alcu on the XP2500+:

CPU Temp
° C/W

The noise level at 4V is much quieter than at 5V. Instead of being close to the Panaflo at 9V, it's closer to the Panaflo at 7V or less. It is tough to discern exactly, because the level IS very quiet, and to gauge differences between two quiet sources accurately, all other noise sources need to be eliminated (including fans and hard drives of the test systems, etc). This being the helter-skelter days just before the winter holidays, it is not possible to set up such testing right now, it will have to wait for another time. Nevertheless, the above result shows that cooling effectiveness of the 7000 extends down even to 4V, and this may be a viable option for 7000 users who wish the very lowest noise level.

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