Would covering walls with a sound absorbing foam reduce the transmission of medium-high frequency fan noise?

Question

I have recently purchased a server-grade computer, which works great, however, it is now audible even through a closed door.

It is in a separate room, so I am thinking what are the best ways of sound-proofing it.

Does covering the walls with a sound-absorbing foam make sense?

My plan is to cover the area around the server, potentially also adding another partition of the sound-proof foam around the machine to further dampen the noise.

Any recommendations? The room is approx 2m by 1m, so quite a small one.

EDIT1&2:

Further advice suggests that a sound-dampening box around the server may be a good solution - what would be a good material to use? The noise producing machine is Dell 2950 (see link for example of the sound)

EDIT3:

I've taken a sample of the noise using my phone see image: noise spectrum. From what I can see, after the fans initially spin up, they settle down at just below 1kHz. Then, at the bottom is most likely the PSU fan, which spins normally at 4kRPM, half speed of the main fans. Hard to read the scale but I guess the main band is just over 0.1kHz. Although the colour may indicate similar pressure, the PSU fans are much less audible.

Answer 1

Easier than sound-proofing a room would be to build a sound-proof box for the server using the triangular foam. Since it's a rack-mount server, just building some ducts for the front and the back and lining the ducts with the triangular foam you linked to above may be enough.

An even better alternative might be to replace the system fans with low noise counterparts.

Answer 2

I am a master electrician and I have been on numerous projects with server rooms. Most of the time a good wall insulation works well to sound proof, if you can access the inner walls. There is another option that is a little pricey it's called sound soak. It is a fiberous panelboard that someone can order from a building supply house. You anchor metal channels vertically to the wall and the panels interlock together with the metal channels. This provides a void space between the wall that acts as a barrier and the fiber board prevents sound from passing through.

Answer 3

A material like this is designed to absorb and scatter sound. With medium frequency fan noise, it usually goes a long way to nearly eliminating the sound. If it were lining a box—even a partial one like a partition—and also covering all walls and other surfaces, it should be satisfactory.

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Also, you might inspect the gap under the door. If it is higher than it needs to be, some weather stripping under the door should help considerably.

Answer 4

Acoustically isolating a room can be a non-trivial task. Normally this makes sense where the interested party does not have control over the source of the noise, e.g. a recording studio sound booth.

When the interested party has control over the source of the noise, it can be more cost effective to address the source than to throw money at construction. For example, acoustic isolation of a source often requires modifying doors, their frames and hardware and/or installing separate HVAC systems to eliminate flanking paths.

Specific acoustical solutions require harmonic analysis of the noise source. This may reveal that masking is better than isolation.

Answer 5

The main source of noise on a server are the cooling fans. The wikibook Noise from Cooling Fans shows the spectrum of a typical 120 mm diameter computer fan:

Note that the sound power is in decibels relative to some arbitrary scale and not sound pressure level. While there is a long tail, most of the sound power is at frequencies near (and below) 250 Hz. You are going to need at least 40 dB of attenuation in order to get the server sound down into the noise floor. If the server has multiple fans, you will need more attenuation, but attenuations do not add lineally. You would add 3 dB for every doubling of the number of fans: 1 fan is 40 dB, 2 fans is 43 dB, 4 fans is 46 dB, 8 fans is 49 dB. The real issue is not the amount of attenuation needed, but the low frequency nature of the sound. Attenuating low frequencies is much more difficult than attenuating high frequencies. The cheapest solution is going to be to replace noisy components of the server with less noisy components (e.g., replace fans with water cooling).

If you really want to isolate the server, you are probably going to have to take a mixed approach of stopping the transmission of the sound by placing it in room/enclosure/box with thick walls made out of dense material (e.g., concrete) and absorbing the sound with a soft low density material configured in a way that you get lots of reflections. Auralex has some nice published data on Noise Reduction Coefficient (NCR) of their wedges and the Sound Transmission Class (STC) of their barriers, but I don't think there is anything special about them as a company or their products. They sell a transmission barrier product that provides 19 dB of attenuation at 250 Hz (15 dB at 125 Hz) that would be a good start, but not enough in isolation. Adding foam wedges will get you further along. The ability of a wedge to absorb sound depends on the frequency of the sound and the length of the wedge; the lower the frequency of the sound the longer the wedge you need. Their 4" wedge has an NCR of 0.85 at 250 Hz and 0.31 at 125 Hz. This may sound like a lot, but 20 dB of attenuation requires an NCR of about 0.9. Combining the two products (or any two similar products) should get you pretty close to not being able to tell the server is on.

Answer 6

It depends on how much you are willing to spend. There are professional sound deadening products such as mineral wool insulation and drywall that are specifically made to block/absorb sound. Some of these products are pretty cost prohibitive and most places don't carry it.

A cheaper solution would be to get normal mineral wool batts and insulate the voids in the partition walls with it. You can also put thicker drywall on the walls like 5/8 instead of the standard 1/2". If you have a hollow core door, you can also replace it with a solid wood door. Another thing you could do is to put down rugs or carpeting if there is a wood floor.

Answer 7

Another approach to take (maybe in addition to some of the other answers) is to try to reduce the amount of noise the server is making in general:

• Some servers can be configured to run the fans at full speed, or to adjust them based on the temperature inside the server. You probably want the latter option. Check the BIOS.
• Similarly, the fans will work harder in a hot room. If the room is hot, see if there is a way to cool or vent it.
• Hard drives generate more heat and noise than SSDs, so you might consider switching some / all of the drives. (Huge performance gains to be had, as well.)

Answer 8

Keep in mind that exposed foam on a wall is a fire hazard, and could be a code violation. Foam itself needs to be covered in 1/2" drywall, or other firebreak.