Quiet MP Dual-CPU Workstation

Do-It-Yourself Systems
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January 7, 2003 by Leo Quan

Introduction by Mike Chin, Editor -- Leo, a graphic designer and visual artist, tells us about his trials and tribulations with a new topic for SPCR: The challenges of cooling a dual-Athlon, dual-hard drive workstation quietly. Leo applies PC silencing concepts freely, modifying them to his needs. He also creates new ways and techniques, and generally goes the whole 9 yards to achieve his ends. While his work is of particular interest to those with a noisy dual-processor machine, it is interesting to any quiet PC modder. You may reach Leo at info at powergyoza.com.

I've tried to quiet my dual-Athlon workstation ever since I first put it together. The very first setup would not be considered loud by overclocking or gaming enthusiasts, but it was driving me mad. It had Thermalright SK-6's w/ Y.S. Tech 60mm 26 CFM fans, 2 Antec case fans as back exhausts and 2 Sunon 30CFM fans as front intakes.

People may call the Y.S. Tech 26 CFM fans quiet compared to the Delta 38CFM and 50CFM screamers, but they were still bloody loud! Ditto for Sunon and Antec case fans. Out went those fans and in came the Panaflo L1A 80mm fans for the case and Panaflo H1A 60mm fans for the SK-6's. I could instantly hear the improvement, and I was even satisfied with the setup for a while.

But I wanted better. Better as in, "I want to hear the movie, not the whirr and whine of the computer." Better as in, "I wish I could sleep at night while my 'puter crunched away at RC5/Folding@Home."

Editor's Note: Here's a preview of the final result of Leo's work. See if you can spot all the little tricks and techniques Leo artfully applied. Pop quiz later!

BASELINE SETUP

My dissatisfaction led me to the purchase of a pair of Thermalright AX-7's and Panaflo L1A 80mm fans. I figured that by removing the 60mm Panaflos H1A's (rated at 0.17A and 19.1CFM and quite noisy), I would eliminate most of the racket. The hard drives were an obvious problem too, but I couldn't afford the time and expense of getting new hard drives and reinstalling all my applications and data. So with the AX-7's in place, I had my baseline setup.

Editor's Note: A look at his PC before Leo caught the quiet bug. A blue nostalgic look?

Call my standards low, but it was a decently quiet machine. It was certainly quieter than my old K6-500 rig that had 4 hard drives! That old thing had a Quantum Viking II and was a horribly loud bugger! Still, I had many improvements that I could make to quiet my hot dual-Athlon baby. I certainly had cooling headroom with this setup. My Athlon MP 1600+'s were running quite cool, as were the hard drives. I could surely sacrifice some temperature headroom for a quieter setup. This was my "before" setup:

Antec SX-1040 case w/ Panaflo 24CFM fans (2 rear exhaust, 1 intake for hard drives)
Antec SmartPower 400W power supply
Tyan Tiger MP (2460)
2 AMD Athlon MP 1600+ @ stock voltage and MHz
Thermalright AX-7 w/ Panaflo L1A fans (12V, blowing)
2 GB RAM
2 Maxtor D740x Hard Drive (40 GB and 80 GB, ball-bearing models, rigidly mounted)
Floppy Drive
Lite-ON 24x10x40x CDRW
Pioneer 305S 10x SCSI DVD Reader
Matrox Millenium G550 Video Card
D-Link DFE-538TX NIC
Pinnacle DC30+ Video Capture Card
Tekram 395 SCSI Card
Samsung Syncmaster 700NF 17" monitor
A couple other SCSI peripherals

System Power

The total AC power draw of the system was measured with a Kill-a-Watt power meter.

  • At idle, it measured 210W.
  • At maximum, it was 250W

If one assumes 70% PSU AC/DC efficiency, this translates to

  • At idle, 147W DC power delivered to components.
  • At maximum, 175W DC power delivered to components.

Maximum power was the highest peak seen with CPU stress testing plus random opening/closing of CD drives with disks in them to force

Noise and Temperatures

Using an old analog Radio Shack sound level meter and the temp monitors from my motherboard, I registered the following readings:

Baseline Setup Sound level (dBA)
Front of case (0.5" distance from case at HDD height)
62
Hard drives (inside case between 2 hard drives)
70
Exhaust fans (outside case, near corner closest to fans)
69
CPU fans (between sides of 2 CPU fans)
69
Temperature (C)
CPU 0/CPU 1 (stressed with CPUBurn - BurnK7)
51 / 48
40GB/80GB HD (Dtemp)
38 / 34

Although the other readings were higher, I considered the 62dBA front of case measurement to be most important. The front of the case has the most direct path to my ears while I'm working or using my workstation as an HTPC. In addition to making my computer sound quiet to me, I also wanted to reduce this measurement as much as possible. I was sure I could do this as I had lots of cooling headroom that I could take away from CPUs and the hard drives.

THE MODS

With the advice and encouragement of SilentPCReview's Mike Chin, I took on the challenge to quiet my computer. The project consisted of quieting all the major noise producers: the fans, the hard drives, the power supply and the case itself. ( Editor's Note: In fact, the project has engulfed Leo's life and trapped him in a never-ending cycle of mods and more mods. I'm really sorry, Leo! Someone please rescue this man!)

This article was originally written in a chronological fashion. Later, because of all the going back and forth I did with so many mods, that approach was more or less abandoned. It might be best regarded as a collection of related noise-reduction experiments on a dual-CPU PC.

1) Undervolt fans to 7V and remove intake fans

Undervolting the fan was a simple mod that only required swapping some power leads of the Molex power connectors. Instead of connecting the negative terminal of the fans to the ground line, I connected them to the 5V line. I have no variable voltage but I have 7 volts! Judging from Mike's high end cooler shoot-out, I figured that 7V was the lowest I could go anyway.

Case & HS fans @ 7V
dBA
ChangeB*
Front of case (0.5" from case at HDD height)
62
0
Hard drives (inside case between 2 hard drives)
70
0
Exhaust fans (outside case, corner closest to fans)
69
0
CPU fans (between sides of 2 CPU fans)
69
0
Temperature
C
ChangeB*
CPU 0/CPU 1 (with BurnK7)
64 / 56
+13 / +8
40GB/80GB HD (Dtemp)
NA
NA

*ChangeB = Change from Baseline

While my CPU temperatures jumped, I gained no improvement in noise levels. In fact, I could hear my power supply fan work harder, probably because the undervolted exhaust fans were allowing more heat to build up inside the case. I could hear the pitch of the fan noise slowly pick up after only 5 - 10 minutes of turning on my computer.

2) Replace the PSU fan with a quieter model

The 80mm fan that came with my 400W power supply was a 38.6 CFM Adda ball-bearing unit (AD0812HX-A70GL). It's specs are listed as 0.25A, 3010rpm and 34dBA. I tossed that fan out and replaced it with a quieter 18CFM NMB ball bearing unit (DC3110KL-04W-B19). It's rated at 0.06A and 18dBA.

I ran into some trouble with connecting the new fan to the header. The header is some sort of 2 pin mini connector, smaller than a Panaflo 2 pin connector, but thankfully still the same pitch. In my attempts to get the connector to fit to the header, I dislodged the balls of solder connecting it to the PCB! Nothing that some solder can't fix. In the end, I found that I could shave a Panaflo 2-pin connector enough to fit.

Quieter NMB PSU fan
dBA
ChangeB
ChangeP
Front of case (0.5" from case at HDD height)
58
-4
-4
Hard drives (inside case between 2 hard drives)
60
-10
-10
Exhaust fans (outside case, corner closest to fans)
64
-5
-5
CPU fans (between sides of 2 CPU fans)
63
-6
-6
Temperature
C
ChangeB
ChangeP
CPU 0/CPU 1 (with BurnK7)
66 / 61
+15 / +13
+2 / +5
40GB/80GB HD (Dtemp)
NA
NA
NA

*ChangeB = Change from Baseline; ChangeP = Change from Previous

This modification made a noticeable acoustic improvement. The noise levels all around the case went down. The most audible components now were the hard drives. My components were running a bit hotter still and the exhaust from the case and PSU fans were quite warm, but my computer was still stable. These results cannot be attributed entirely to the change in PSU fan. Before I took these measurements I also inverted the HS fans so that they'd be sucking and made a exhaust duct so that the hot exhaust would be vented out directly.

3) Decouple Mount the Fans

Rather than buy elastomer fan grommets, I cut up 2-3 inch pieces of soft foam and used them as grommets as shown in the photo below. The foam pieces get shoved through both the panel mounting hole as well as the fan mounting hole. Friction keeps them in place.

The little strips of tracing paper hanging off the fan opening help me confirm with a quick glance that the fans are working: the light paper strips flutter in the breeze -- or at least stand up a bit even when the fan is running slow so I can't hear it easily.

The drawing below details how the foam grommets are installed. Not pretty but that's not a real concern for me. It is very effective at reducing mid/low frequency noise caused by fan vibrations.

Here is a photo of the inside, showing how the red colored electric tape was used to close the gap between chassis and fan to minimize airflow diffusion. I don't believe the tape short circuits the mechanical decoupling of the foam grommets, but I have not seriously tested this.

Also visible in the above photo: Two small pieces of foam were also used as decoupling washers on the screws used to mount the 80mm Panaflos on the CPU HS, one between HS and fan and another between screw head and fan.



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