Drop a decibel and clean up the clutter on the back of your tower with this cheap and easy mod. You can purchase power-supply ducts and rear fan ducts, but often they use thin foam and block more air then this. You can also use this to funnel the hot air into any direction if your tower is in a cramped area.
Plastic Shoebox $1-2
Foam, Sound-proofing material
Something to cut the plastic.
Attachers-Velcro or magnets or mounting tape or poster putty.
Step 1: Materials Needed
I purchased a smoke black shoe-box from Wal-mart for a $1.25. The depth of the shoe-box is compact enough to look good, but still allows for the exhaust fans to push the hot air out. On the left is acoustic mat foam that you can purchase from most computer on-line stores. It costs about $20 but you get enough to do a mid-tower and have enough left over for this project. If you want a cheaper option for 50 cents you can purchase the art foam at Wal-mart in the art supplies/craft section. You'll also need something to cut the plastic and attach the shoe-box to the back the of the PC. I used a Dremel and Velcro, but you can use whatever you have on hand.
Step 2: Cut Out the Shoe-box
Use a Dremel, sharp knife or scissors to cut out one side of the shoe-box. I left the rolled edges intact because it looks nicer and is more sturdier.
Step 3: Line the Shoe-box With Foam and Attach It to the PC Rear.
The acoustic-mat and the foam both have a self-stick backing so peel and attach to the inside of the shoe-box. (If you buy the expensive foam leave the backing on and tape it to try it out first. This way if your not happy with the results you can reuse the foam.) If you have chunk foam you can also use this. Make sure to leave enough space between the foam and the exhaust fans to avoid pushing the hot-air back into the computer.
Attach the shoe-box to the back of your PC. I used Velcro to make it easily removed.
**Don't expect a night and day difference**
What you will get is a slight reduction, mostly in the higher pitched sounds.
This is just one more thing you can do besides using quiet components and lining the inside of your tower with acoustic-mat.
**Don't be surprised if your case temperatures go up a degree**
The box is deep enough to allow the the air to leave the case, but the hot air isn't getting pushed as far.
Alternatively by turning the shoe-box you can have the exhaust vent up. Not necessarily a quiet option, but it does provide optional airflow in a cramped corner.
My first Instructable here, so sorry if it sucks. I think the idea is worth a try and it beats paying $20 for the ones you purchase only to find out they don't reduce the sound that much.