Noise. Constant noise is distracting. I've worked in an enterprise data center
and it proves to be quite challenging to think clearly after a while. Since the NETPOOL project
requires a small cluster of machines, I went all out and bought a server rack. It's an old rack
with rust in a few spots, the cabinet fans long since had siezed up (which I replaced), but it came
with rails and had some rough shelves already set to host 4U cases. It even had some custom housing
for 110v electricity (which I wired myself). Perfect.
...Until I get it home
and realized how loud an undampened sheet metal cabinet truly is, aggravated by mostly blank walls and
tile floor. Most of the time, the machines
are off, but the hub stays on 24/7, and made a lot of racket. This page shows how I took care of
it. While I was at it, I decided to modify the only computer I keep OUTSIDE the cabinet--my desktop
machine--to keep the noise down as well. Keep in mind, my results are very subjective because I don't
have a decibel meter, but my wife doesn't refuse to enter my office anymore, and I can actually talk to
people on the phone now. Total Time: 3 hours
So, I went shopping. Of course, the D.I.Y. in me wanted to play with this stuff anyway, so
this was my opportunity.
I came home with:
- Two 2' by 4' sheets of 2" wedge foam from Auralex ($20 each from GuitarCenter)
- One 4 sqft. WedgePack of Dynamat Extreme vibration dampening adhesive ($35 from XtremeSound).
- Some eye hooks and string (less than $2), for hanging baffles, and
- Super 77 spray adhesive from 3M ($9).
- Foam weather stripping for doors
Don't buy any adhesives they sell where you buy acoustic foam! It's twice the cost for
the same product. Go to your local hardware store. Be sure the adhesive you purchase
indicates foam on the label
, as some adhesives have solvent-like qualities and will dissolve
Also note that there are two types of Dynamat: Original and Extreme. The Original style is cheaper,
but rigid and requires heat to bond. The Extreme is a little more expensive, but is very tacky and
easily sticks to surfaces. I bought the Extreme, since that's all the local dealer had, but after
using it, I don't think I'd bother with the Original unless you're really cheap or have lots of time
on your hands. According to the salesman, who has installed both types, Original takes 3x longer to
As in everything else, 80% of the noise will come from 20% of the components. Tracking down the
worst offender and dealing with it directly (i.e. replace fans, tighten case screws) will yield much
better results than secondary noise cancellation or absorption.
My Achilles heel was my old, ratty 100baseTX hub.
It has two thick microfans that push a lot of air around, but both together would set up sympathetic
vibrations in the case after a few seconds and it wouldn't shut up. After trying some felt tabs, I
tried using epoxy to glue them tightly to the case. Finally, I realized it was the fans themselves, but
one was much worse than the other. So, I replaced the loudest fan with a new microfan with similar
dimensions, though half as thick. This was about $1 at a local electronics store.
I take no responsibility if you burn your house down. If you aren't sure, don't tinker.
This smaller fan pushes half as much air around at the same power rating (0.1A * 12vDC = 1.2W),
but it was much quieter, so it's a risk I'm taking.
Next, I took out the Dynamat Extreme (see how sticky it is?) and cut a piece to fit the inside of the
hub's case lid. It's hard to see from the photo, but the reason I only covered the back half was
headroom. The lid is nearly in contact with some electronic, and is certainly in contact with some
heat sinks around the power supply, for safety presumably. Rather than foul it up, I left it alone.
In hindsight, I think I probably should have put a few small squares where the heatsinks come in
contact, to dampen vibrations more; doing so might heat the Dynamat and release chemicals, or even
catch fire under the wrong conditions, so I chose not to.
Since the rack cabinet has a smoked plexiglass front door and I rather like seeing the lights flicker,
I only dampened the back door with Auralex.
The back door simply lifts off its hinge pins, so I removed it and set it down on the tile floor.
Because of the inset lock and handle, one side will have a gap in foam. Also, the middle strip is
at a different depth than the sides. Ultimately, that just means more cutting and gluing, but is
quite easy to do.
For cutting the foam, I tried using measuring tape and a scalpel-like razor blade knife, but if
you notice the results in the picture, it didn't turn out so well. The edges were rough because it takes
several passes to cut the material with so small a blade. Instead, (my wife's suggestion) using scissors the
cuts were much cleaner and faster. Hmmph. Women.
So, after each piece is cut, I laid them in place and measured for the next. The foam is quite pliable,
so don't sweat a centimeter here or there. The most important thing to pay attention to is placement:
you don't want to put foam anywhere it may obstruct servicing the unit. I thought I was careful, but was
forced to remove a bit from each part during assembly, because I put a little foam in the way of a fitting.
The cabinet lid is the only other part that is accessible, flimsy enough to vibrate, and is in contact with
moving parts. In other words, it's ideal for damping. The only tricky part is getting around the fans,
and that's a snap because they're square.
As you see in the photos, I cut a chunk big enough to cover most of the lid, minus an inch or so on each side
(and wasn't quite enough) for fitting purposes. Eyeballing the cuts was pretty simple, just by peeling
back the foam and cutting in place. Be aware that cutting along the trenches is much preferable to cutting
across the wedges.
It's a lot easier to get good results, and takes a bit less time. Take that into
consideration before making your first cut (I didn't), so you minimize the work you make for yourself.
The spray adhesive is pretty sticky stuff (duh), and has a horrible odor that lingers. I took all materials
outside and propped them on a sawhorse to apply it. It's very straightforward, especially if you aren't trying
to use a camera simultaneously. All I had to do was remove a section of foam, spray the metal, spray the foam backing,
count to ten and stick it down, carefully pressing each wedge into the metal. This particular adhesive is tacky for
about half an hour, so if I messed up, I could pull it back up and resituate it. AFter about ten minutes, I
brought everything back inside to avoid rain, but I'd rather leave it out overnight in a well-ventilated area.
My office does smell a bit like glue now.
The lid was more interesting because of the fans. Since the mechanisms are fully enclosed on the sides, it's only
important to keep the bearings, fan blades, and the electrical connector free from overspray. I pulled a couple
of small kitchen trash bags out for help with this. Once tightly wrapped around the fan, I twisted and bound
the excess with tape to keep them in place. With that out of the way, and the electrical cords removed from
the fans, I went ahead and bonded the foam to the lid.
Here is a shot of the lid after placing all the foam. Of course, both plastic bags were sticky as hell and various
foam bits wanted to come up with them as they were removed, but it worked out remarkably well.
Well, the above takes care of the back and top. The base of the cabinet is resting on four square wooden shelves
that I had laying around. This keeps my tile floor from getting scored while keeping noise down. Wood is a pretty
good insulator. The sides are heavy and have rack hardware welded onto them, so there's not much I can do to improve
the vibrational characteristics there. The front door was another story, though.
This is an older cabinet, so some parts are just plain bent or hard to adjust or rusted shut. All I wanted
was to block any open-air pathway for sound to travel.
So, I removed the thin metal plate above the
door and added a strip of 40 mil EPDM rubber, much the way you put a floor sweep on an exterior house door.
EPDM is easy to puncture or rip, so this is obviously not ideal if you will be messing with components in the top
of the rack a lot (I won't be). You can buy EPDM rubber at Home Depot, Lowes, or any pond store, typically sold as
rubber pond liner. For this sort of application, a scrap 2' by 4" is plenty, and shouldn't cost you anything.
Next, I took the foam weather stripping and stuck a long strip down the inside jamb. The outer edge of
the door has a long magnetic strip that seals the door, so no need to mess with that. The bottom
of the door was just separated by a small distance from the cabinet when the door was shut, so I put weather stripping
along the base of the door as well. Now the front door, while not being very sound absorbing, didn't leak air
much anymore, if at all.
This next part isn't very pretty, and I'll probably do it over again someday, but it'll suffice. Since my office is
so acoustically live, the best place to trap sound is close to the source, where the power per surface area is greatest.
My rack is in the corner, which gives it three straight surfaces to create reflections. This may help a little in trapping
the sound against a floating baffle, because at least half of the signal's escape routes reflect into the foam.
Ideally, this would be a double-sided wedge of foam, but since it's a scrap, I make do with what I have left over.
Also notice that the hooks are inset from the edges to add some concavity up toward the ceiling, which I figured would catch
reflections better than a planar arrangement. Honestly, it's hard to say what difference it's mades, as the above
modifications had such a tremendous impact.
Now, on to the loudest box that remains. My desktop has a nice Enlight mid tower case, which I bought specifically
because it had easy access slide mount rails and an extra drive bay. Having rails makes the case wider than usual, adding
a little more air space and room for cabling. I've really enjoyed it, but because of all the toys I've
crammed into it, it's about the loudest PC I've ever heard. I suppose that's fair, since there's a 0.24TB RAID-0
dual Celeron with Alpha Coolers, an additional case fan, and a special hard drive mount that takes up two 5.25" bays
with a large front fan to keep the drives cool. This latter component has space for three drives, but even with the fan
they got so hot that the middle one fried its controller board in less than a week, even with the side of my case, and blew
the RAID. I've got rounded IDE cables coming in the mail that should take out some of the clutter and improve airflow, since
I have five ribbon cables taking up space in there. Don't worry about the wad of power splitters at the bottom, it's a 300W
power supply, and has run rock solid for a year with full load and no down time.
As you can see, a full sheet of Dynamat Extreme is plenty large for a computer case. I was tempted to put it all over
the outside of the case, but after playing with it a bit, you really don't want to do that. Basically, it's a metal foil
on one side, a brown waxed paper on the other, and sandwiched between is this gooey black putty substance that sticks to
everything. You wouldn't want to brush against it--I was picking little black tarballs out of my leg hair the next day,
and I was careful.
So, I cut the tarpaper with scissors into a shape that fit the open-side of my case well, careful not to cover any air holes
or get too close to the edge. In retrospect, I should have put a bigger piece on that side, at least covering up the lump
you see in the photo. Still, it works fine to add weight and dampen vibration.
Dynamat sells a hard roller that helps you get the air bubbles out, and it's important that you do press the material down
hard to make a good bond, but I don't think you need the roller unless you're doing a bunch of installs. I went to my
cupboard and fetched a handy plastic bottle of whole pepper and used the butt to work out the foil side once it was placed.
It's kind of like flattening a Hershey's kiss wrapper, and quite easy to do, but requires a little elbow grease. You should
hear a few pops around the edges if you're doing it right, because you're squeezing out the air bubbles. Black tarry goop
should also spread out from under the foil. If that bothers you (as it did me), take scissors or a knife and cut along the
edge, and roll the goop away like you would dried glue. It looks quite clean and professional when you're done.
Here's where I took the motherboard-side panel off. Since it comes into direct contact with the frame that holds the board
in place, it's a much tighter fit, even as thin as the Dynamat material is. I was nervous about ruining the panel, but it
turned out fine. Again, the only problem was getting too close to the clips around the edge, which I had to cut back a bit.
This panel is very heavy now, and does not vibrate very much, even with a full concourse of fans humming. It feels quite solid
when you rap your knuckles against it, too, and gives a solid satisfaction of quality.
Last, I tried to deaden the air outside the case as much as possible, forcing airflow through fan ports (and hence, sound) in hopes
that the spinning fans would act somewhat like spinning baffles, randomizing reflections. I took some peripheral port faceplates
from another machine and screwed them into the two empty ports I found. Two further improvements would be to add a thin foam filter
to the front-facing intake fans, and to seal the air holes in the access panel with more Dynamat. This final step would have some
very negative effects on temperature, however, as the case vents much of its pressure here.
The rack cabinet is almost silent. The components in the rack are a good bit quieter on their own,
but while the doors are shut, the noise is completely acceptable, akin to having a small fan on in the room,
which is largely only the sound of the twin fans in the lid.
My desktop machine is certainly quieter than it was. With all panels on pre-Dynamat, it was noisy, but
with all the enhancements, it's tolerable, though still louder than I'd like. It's about as loud as having
a microwave constantly running, again because of the fans. There's not much I can do about that except buy quieter
fans. Because of this, I'll probably put it in on shelf in the cabinet and get some cable extensions. Heh.
Desktop Stats Before Dynamat: CPUs: 34C-44C, Avg 42C. Chipset: 36C-50C, Avg 38C
Desktop Stats After Dynamat: CPUs: 35C-46C, Avg 43C. Chipset: 38C-51C, Avg 39C
So, as far as this project goes, I think it's a success. In retrospect, I think the Dynamat stuff is pretty good,
but acoustic foam, sealing open air ducts, and quieter fans may be the best way to go.