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10-02-2013, 11:16 AM
I've asked a friend to answer you since he knows a thing or two about this very subject -
Ultimately, it depends on how much attenuation you’re trying to achieve and at what frequency(s). Since we’re talking a garage and a Porsche, I imagine the lovely 80db growl between 50-300 Hz is the main thing that is rattling the neighbors, which of course happens to be the toughest to work with.
Sound travels in two ways, through the air and via vibration through materials. I’m sure you’ve observed that lower frequencies cause more vibration than higher frequencies. In this case, slapping foam on the walls will only attenuate frequencies above 300 Hz (which will not address the real problem). The only solution here is to add mass to stop the transmission via the air and add a layer of isolation so the vibrations do not transfer between surfaces. Putting foam/carpet/egg crates on the wall will have some effect, but it is probably a waste of money. Below are some options, none of which are necessarily cheap, however the cost could be minimized if you have basic carpentry skills, a few friends, a case of beer, and only the offending wall is treated.
1) Add a layer of 5/8” drywall to the existing drywall. (-5db)
2) Build an air pocket using ¾ furring strips in front of the existing drywall 24” on center. Then attach 5/8” drywall to the furring strips (-15db, maybe more). The wide spacing of the furring strips minimizes the points where vibration can pass from wall to wall. Adding a second layer of 5/8” drywall will probably drop it some more, but you’ll need to reduce the spacing to carry the weight. Probably not worth the cost/effort as you’ll only gain an extra 3-5 db.
3) And finally, the correct way to “sound proof” a room (-40db+):
- Frame a 2x4 wall 16” on center spaced 1” from the existing wall (metal studs will transfer less, but wood’s fine too).
- Add R12 insulation between the studs.
- Attach 2 layers of 5/8” drywall to the newly framed wall.
Ultimately, it depends on how much attenuation you’re trying to achieve and at what frequency(s). Since we’re talking a garage and a Porsche, I imagine the lovely 80db growl between 50-300 Hz is the main thing that is rattling the neighbors, which of course happens to be the toughest to work with.
Sound travels in two ways, through the air and via vibration through materials. I’m sure you’ve observed that lower frequencies cause more vibration than higher frequencies. In this case, slapping foam on the walls will only attenuate frequencies above 300 Hz (which will not address the real problem). The only solution here is to add mass to stop the transmission via the air and add a layer of isolation so the vibrations do not transfer between surfaces. Putting foam/carpet/egg crates on the wall will have some effect, but it is probably a waste of money. Below are some options, none of which are necessarily cheap, however the cost could be minimized if you have basic carpentry skills, a few friends, a case of beer, and only the offending wall is treated.
1) Add a layer of 5/8” drywall to the existing drywall. (-5db)
2) Build an air pocket using ¾ furring strips in front of the existing drywall 24” on center. Then attach 5/8” drywall to the furring strips (-15db, maybe more). The wide spacing of the furring strips minimizes the points where vibration can pass from wall to wall. Adding a second layer of 5/8” drywall will probably drop it some more, but you’ll need to reduce the spacing to carry the weight. Probably not worth the cost/effort as you’ll only gain an extra 3-5 db.
3) And finally, the correct way to “sound proof” a room (-40db+):
- Frame a 2x4 wall 16” on center spaced 1” from the existing wall (metal studs will transfer less, but wood’s fine too).
- Add R12 insulation between the studs.
- Attach 2 layers of 5/8” drywall to the newly framed wall.