StealthPC Foundation Kit by ARM Systems

Cases|Damping
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TRIAL APPLICATION

To find out how well this prototype StealthPC Foundation kit works, it would have been great to compare it with one system against another identical one without the PSU intake duct. Unfortunately, a second case was not available to me at this time.

An Athlon 64 3200+ System

I assembled a system with this prototype StealthPC Foundation kit:

  • AOpen AK89 Max (nVidia3 Athlon 64 board)
  • AMD Athlon 64 3200+ (spec'd at 89W)
  • Zalman ZM7000A-AlCu heatsink w/ fanmate1 set to 5V
  • ATI 9800 Pro VGA with Arctic Cooling VGA Silencer (fan set to low)
  • Crucial PC3200 memory, 512MB
  • Samsung SP0802N hard drive, mounted with the supplied EAR soft grommets
  • Samsung SM-252B CD-RW Drive
  • 120mm exhaust & intake fans (as supplied in the kit) set to 5V

The so-called RamAIR Cold Air Induction CPU Duct System — i.e., the side CPU intake duct — is adjustable for height (or depth) and can also be moved from side to side. With this motherboard, the duct ended up slightly too high and too far back. It can be moved easily enough, and I don't doubt that better positioning would improve CPU cooling (and maybe even case temps) by a few degrees. However, the duct stayed where it was. The inflow of air through the outside opening of the duct could easily be felt; I am sure it helps.

The maximum AC power draw of the system was with CPUBurn stress testing: 165W. That number represents the total heat in the system.

Silent Nutter's Rig

This is 26W higher than my main rig, a P4 system that hits max AC power of 139W. This system differs from the above in the following ways:

  • Intel P4-2.53
  • Zalman ZM7000-cu @ 4.5V
  • AOpen AX4GE Max motherboard
  • Matrox G400 Max VGA cooled by Panaflo 80L at 6V with exhaust port created by removal of PCI slot covers
  • Seagate Barracuda IV 40G x 2 hard drives in DIY elastic suspension
  • Panaflo 80L fan at 6V for intake & HDD cooling
  • Selective sound damping on interior case panels
  • Zalman ZM300A PSU modified with Panaflo 80L fan; entire PSU located on top panel, outside case.

A unique aspect of this system is that the PSU is running OUTSIDE the case, and thus completely unaffected by any of the heat in the case. Another benefit of this arrangement is that the case airflow is greatly improved by the absence of the PSU in the top corner. Instead of a 30-40W source of heat, there is a gaping hole, an exhaust vent of about 5" x 3" through which rising hot air evacuates from the case. There is no back case fan; the 80mm hole for it is left empty. Only convection is used for heat evacuation from the case.

In a nutshell, this rig is...

  • Totally tweaked over the course of nearly two years with the quietest components I have found or modified.
  • Utterly impractical and unsellable as a commercial system.

To compare this customized and hacked Silent Nutter's Rig against a hotter system slapped together in a morning in ARM Systems' eminently practical Foundation Kit is patently unfair. But that' precisely what I am going to do.

Both systems were placed on 1.5" thick pieces of closed cell foam for acoustic insulation from the hardwood floor under the desk in my home office, which measures just 10' x 10' (with a 8' ceiling). The middle of the floor is carpeted. The sound level meter was placed 1 meter from the front or back panel each computer on a cushioned chair with the microphone at the same height as the top of the case. Here are a range of relevant measurements after half an hour of CPUBurn on each PC. (In both cases, temperatures stabilized and remained unchaged after 15~20 minutes.)

CPUBurn: 30 minutes
StealthPC Foundation kit Athlon 64
Silent Nutter's Rig
Noise Front
26 dBA/1m
21 dBA/1m
Noise Back
29 dBA/1m
24 dBA/1m
CPU*
56°C
59°C
Case*
44°C
45°C
PSU Temp**
37°C
32°C
AC Power
165W
139W
* These temperatures are not directly comparable, but provide a rough guide.
**Thermal probe within 1cm of PSU exhaust, positioned for highest reading.
Room Ambient: 25°C and 17 dBA

One very important thing to note with the above table is that there is no minimum and maximum for noise levels: Both system stay at the same noise level whether at 100% load with CPUBurn or idling with AC power at 70% of the max. This is because the case and CPU fans were at fixed low speeds, and the thermally controlled PSU fan never ramped up in speed in either system.

When you consider that my Silent Nutter's Rig PSU had the cooling benefit of being entirely out of the hot case and handling 26W less heat, you can see that the ARM Systems PSU fresh air duct system really does work. The exhaust air temperature from the Foundation kit system was substantially hotter, but still cool enough to keep the PSU thermistor from ramping up its fan.

It is easier to describe the acoustic signature of the Foundation kit system more by what it doesn't do than by what it does:

  • No case vibrations or resonances
  • No whining or high frequency noises of any kind
  • No big whooshing airflow turbulence noise
  • No intermittent louder/softer noises
  • A small amount of HDD noise during seek, very muted
  • A bit of bearing chatter or whirring, especially late at night when the ambient noise is very low

CONCLUSIONS

Is the 5 dBA difference between the two systems audible? Yes. In the daytime ambient of my home office (low-to-mid 20s dBA), the Nutter's Rig is usually not audible where the nutter usually sits. The Athlon 64 system assembled in the StealthPC Foundation kit is a bit over the cusp of audibility. Much of this can be credited to the 120mm fans. The fans are the one area where some improvement can be made... but I am not sure that I have heard any that are significantly quieter. Quiet 120mm fans are tough to come by. It has to do with the sheer moving mass of the blades, the larger size of the bearing, the higher volume of air it moves. Maybe >$20 Papst fans could give better performance but at this low speed? I am not sure. I doubt any system with 120mm fans could best my Nutter's Rig with its Panaflo 80Ls hand-picked for lowest noise at low voltage. (I know that comment is probably going to be seen as a gauntlet by many dozens of SPCR regulars...)

Is 26 dBA at 1 meter loud? Heck no, it is very quiet. For anyone who is used to "normal computers" it is probably going to be heard as silent for a week or longer. If your ambient noise is higher than mine, then you may perceive it as silent forever. But your background noise is similar, then you will become acclimatized to the new lower noise level and hear these 120mm fans. Regardless, it is a very quiet level, especially for a system as powerful as this one.

Can a system quieter than 26 dBA/1m be built using the ARM Systems StealthPC Foundation kit? Yes. The noise floor is set by the Panaflo-modded fresh-air ducted Zalman ZM400B power supply, which is at 20~21 dBA. The trick is to find case fans that are substantially quieter and still move enough air. With cooler components than what I chose here, it should be feasible to use even 80mm fans at low voltage for a noise level similar to my Nutter's Rig. But chances are, you'll probably be more interested getting the StealthPC Foundation kit with an eye to a quiet high performance machine. (ARM Systems says they've assembled and shipped some burning-edge P4-3.4EE systems with this new PSU duct system that has the same acoustic signature as the significantly cooler P4-3.2 system I tested earlier.)

Unless you go crazy with noisy, hot components, it's hard not to make a quiet system with ARM Systems' StealthPC Foundation kit. You get:

  • One of the best ventilated mid-tower cases with the best acoustic bezel design
  • PSU fresh air duct unavailable elsewhere unless you DIY
  • Great acoustic damping materials preapplied in the case (a lot of work!)
  • An excellent 400W PSU with high 75% efficiency and ATX12V 1.3 compliance (high 12V line current) modded for extremely low noise, warrantied by ARM Systems
  • Virtually all the parts associated with the case that are needed for a high quality, high performance quiet rig.

It looks like very good value, and hard to beat for sheer thermal / acoustic performance. Especially if you value your time at all, because ARM Systems have done the research and testing to assemble this quiet package of goodies. That PSU fresh air duct looks to me like the sweet topping on the cake. (Of course, you'll say I am biased because they liked my idea and ran with it... Nah: I am always biased for good simple ideas that work, no matter who comes up with them.)

Much thanks to ARM Systems for the opportunity to examine this prototype package.

* * * * *

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