Hard Drive Sandwich - Revisited

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April 8, 2002 - By Mike Chin

This update of an article first accepted for publication by Overclockers.com in mid-2001 discusses a unique, inexpensive DIY hard drive noise damper that also provides effective cooling. I have added refinements and enhancements developed since the original article was written; these appear in italics.

7200rpm HD: Source of the whineRecently, a new over-clocked 1GHz AMD K7 system raised the noise in my 3-PC networked home office to an unacceptable level. I spent several weeks researching and experimenting ways to reduce PC noise. Eventually, I achieved pretty good noise reduction by dropping the voltage to the fans to 7 volts, applying damping in the case, installing a modified Enermax power supply and doing other mods to improve airflow and reduce turbulence.

Then I began hearing the annoying high-pitched whine of the 7200-rpm hard drive, which had been masked before by fan noise.

How to get rid of the whine?

QuietPC's SilentDrive is the only commercial solution I found: an acoustically damped, sealed enclosure for hard drives. It works by absorbing the noise of the HD. A drawback is that the hard drive heat is basically trapped within the enclosure, and users are cautioned not to use drives that generate more than 6.8 watts of heat. (SilentDrive image courtesy of quietpc.com)

The IBM 75GXP 46G drive is safe, as it generates 6.7 watts of heat. This is the same HD model I use in 2 of my systems. Postings on hardware forums suggested, however, that many users were less than comfortable with how hot their 7200-rpm drives were getting in SilentDrive.

NOTE: Later, I discovered the NoVibe drive mount by Noise Control, which takes a very different approach, essentially suspending the HD with rubber O-rings to decouple vibrations from entering the case and thus cause noise. This product gave me another idea to try; the details are covered in the article Hard Drive Silencing: Sandwiches & Suspensions.

The question became: How to get rid of the whine without overheating the drive?

There are HD cooling fans, but these would probably do little to cool a drive mounted inside a SilentDrive. One consideration was the Vantec Ultimate Hard Drive Cooler, which uses a kind of heatsink and fans to cool the drive. However, no noise reduction for the device is claimed, and I really did not want any more fans.

The solution I eventually came up with is a "noise-sink" that also acts as a heatsink: 2 heavy pieces of aluminum with the hard drive sandwiched in between - thus my moniker for the device.

The accompanying pics pretty much tell the story; here are the details:

  • Four bolts and nuts are used to clamp the hard drive between two aluminum plates, each 3/8" thick, 5.5" x 8", and weighing 630g (22oz). Care must be taken not to over-tighten to avoid potential damage to the HD. Dense foam is wedged around the open sides. I found the sheet metal lying around as scrap in a machine shop and had it cut and drilled for me; I knew my hand held power tools would not be happy working with this thick aluminum.
  • Some HD vibrations are drawn into the heavy aluminum and converted into heat, as the mass of the aluminum plates makes them difficult to vibrate. Higher frequency noise (the whine) bounces off the aluminum plates, and then gets absorbed by the foam. The noise reduction ranges from 6 to 15 dB in the frequencies between 400 Hz and 5000 Hz where human hearing is most sensitive.
  • The close coupling to the aluminum increases the cooling surface and mass. There are significant air gaps between the HD and the metal plates on both sides of the HD. I did not consider using thermal compound - the gaps are too big. Still, maximum temperature is reduced from 45°C down to 38°C (that's a 13°F difference). In normal use, the HD temperature rarely exceeds 30°C, compared to 40+°C without the sandwich mod (an 18°F difference).

The drive sandwich assembly rests on the bottom of the case, just behind the front case fan, which provides additional airflow cooling. A thin piece of foam that came in a motherboard box is used as a damping "bed".

The HD Sandwich may be ideal for water-cooled or very quiet systems where the hard drive is often the loudest component.

Noise Analysis

An anechoic chamber with many thousands of dollars' worth of audio testing equipment was not available to me. :( So I improvised. A demo copy of SpectraRTA software and the microphone of a cheap computer headset plugged into my SB Live! Soundcard were used for noise analysis. The measurement setup was as follows:

1) I isolated the hard drive acoustically in a filing cabinet drawer to reduce interfering noise from other sources. A thick piece of foam in the bottom of the drawer helped reduce reflections. The mic was placed directly on the top center of the drive. A lengthened IDE power cable from a PC allowed the drive to idle. No IDE data cable was used, as the distance to the computer was far too long.

2) Three sets of measurements were made:

  • Drawer closed and no drive inside, as a reference.
  • Bare drive running idle.
  • Drive running idle in Cool/Silent Sandwich, with foam.
The results can be seen in the accompanying images. There is hardly any noise reduction in the lower frequencies. Between 400 Hz and 1.6 KHz, the average noise reduction is well over 10 dB, which is very significant, with peaks of 15 dB or more. Human hearing interprets 10 dB to be twice (or half) as loud. Between about 1.6 KHz and 4-5KHz, the noise reduction is more modest, averaging about 6-9 dB.

Other aspects of the noise measurements:

  • The peak at 50-60Hz on all 3 curves is the resonance of the drawer air cavity.

  • The big peak at 100-125Hz, which occurs only with the HD on, is the vibration of the drive spinning, picked up at a disproportionately high level because the mic was touching the drive. (It's like placing your ear directly on it - you'd hear a lot more low frequency noise than usual.)

  • The mic is not calibrated, nor is its frequency response known. This does not matter, however, as the only real significant data is the difference between the red and blue curves, which is the actual noise reduction effected by the HD sandwich.
Subjectively, with the HD sandwich idling outside the case, it is possible to hear a trace of the "whine" when I bring my head within 3 feet. There is audible noise with seek and write operations. When the HD assembly is in the closed case, if the fans are all turned off, the HD is barely audible.

When the system is operated normally, any trace of hard drive noise (including seek) is completely masked by the quiet "shhhhhh" of the fans. (NOTE: You may not get the same results. For example, if your other components make less noise or if your case is less insulated, you may hear the sandwiched hard drive.)

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