Gentlemen,
I'm in the final stages of building a recording studio, so I hope I can speak with a bit of authority on what it takes to get isolation and sound proofing... whether I want to or not.
Fully realizing that a wood shop is no where as demanding as recording studio in terms of isolation, you can effectively deal with the problem of sound transmission using many of the same principles.
It's important to understand what you're really up against before you can successfully attack the issue with a practical solution.
First, where air goes, so goes sound.
Second, high frequencies tend to move in straight lines, with low frequencies moving more in waves.
This makes high frequencies much easier to deal with than low frequencies. As an example, think about a train. You can hear the low rumble of a train as far as a mile away, but you can't often hear the high frequency squeal of the wheels much past a few hundred feet.
Low frequencies contain as much as 10 times the amount of energy as mid and high frequencies to sound the same apparent loudness. This is a characteristic of the human hearing that has given us the
Fletcher-Munson curve.
Without getting too far into it, the practical outcome is fairly straight forward; This is done by absorbing the sound energy in the material, or by isolating the sound source through decoupling.
1. Mass is the single most effective way to reduce sound transmission, especially low frequencies.
2. By far, gypsum is the single most cost effective mass you can purchase as far as building materials.
3. Mass Loaded Vinyl (MLV) is a bit of voodoo magic in a huge number of applications. MLV is an attempt at increasing the overall mass of a barrier. While it does increase TL, it does so at a cost factor of approx 4:1 (up to as much as 12:1) of simply adding another layer of gypsum... of ANY thickness. MLV is installed in walls and ceilings, by rolling onto the surface and tacking it to the studs. MLV works by damping the vibration of the layer of surface directly in front of it. e.g. hitting a drum with a piece of material laying on it.
MLV cannot be installed tightly stretched. If you do, it begins to act as a resonant drum head and actually REDUCES TL.
It is NOT known how tight to actually stretch MLV for optimal damping in a vertical or OH installation.
4. Resilient Channel (RC) is another often prescribed effective system of increasing TL through attempting isolation.
Many other "channels" are often mistaken for the only product that is proven to reduce sound transmission - RC1.
Hat, Z and H channels are often hyped, but rarely work as effectively as RC1.
There are a number of additional clips that attach to the channel that provide further isolation... but again, this is additional cost for nominal gain.
In dealing with all this complex, often confusing and counter intuitive stuff, the one thing that often gets over looked is HVAC. If you have HVAC that enters your shop, that is shared with your home's HVAC system, you need to isolated the duct work so that sound does not travel as flanking noise, or as direct radiated energy back up the duct work. This is achieved through the installation of a plenum or baffel.
Green glue is an excellent product. I used over 12 cases in my studio, and my TL factors are yielding approximate STC ratings of nearly 84db. Without GG, my engineer estimates we would have been in the upper 70's db range.
To achieve those ratings, I added a LOT of mass in conjunction with the use of Green Glue... along with some pretty sophisticated engineering.
The air cavity within the stud bay of the exterior ( 2x8 ) stud wall has a layer of 5/8" gypsum between each stud. The gypsum is screwed to the exterior sheeting, then caulked along the perimeter and a secondary 1x2 cleat nailed to the stud, binding the gypsum edges to the stud.
The exterior walls were then filled with R-19 insulation, paper inward facing.
Rather than building as I have done, (Room within a Room), with a completely separate 2nd inner wall, ceiling and concrete floor, the next best thing is to face your stud walls with 3/4" sheet goods. I chose OSB over MDF due to cost and concern over potential moisture. Over that layer of OSB, I attached two layers of 5/8" gypsum with a layer of green glue between the gypsum.
The use of sheet goods is far superior to an isolation clip/hat or Z channel... both in terms of structural rigidity, (which creates a denser mass to airborne noise), but it is also cheaper and you cannot short out the channel by driving a screw too far, nor can you miss the channel and create a hole through which you will loose isolation.
You can use any relatively decent construction adhesive on the stud faces before applying the sheet goods. This adds additional structural rigidity and thus compounds the solid mass effect of adding the mass of the sheet good materials.
If you use a hat/Z channel with clips, to gain the TL/STC rating that are tested as per several of the national and international standards, you must use at least double the amount of resilient channel to achieve the same screw pattern of rigidity as outline by US Gypsum, the Canadian Building Standards and the BBC. This effectively triples the cost of using resilient channel solutions over conventional wood frame construction.
To further increase TL in the mid to low frequency range, stud spacing should be increased from 16" OC to 24" OC.
To reduce the effects of noise reverberation and it's associated flanking noise, one of the more common accepted principles used, is to place squares of fabric wrapped mineral wool, or Owens-Corning 703 rigid insulation on the finished surface of walls and ceilings.
If you want to get real propeller head, you can/should further reduce flanking noise, due to impact, by eliminating any connection of the floor to the rest of the structure. This is commonly done by using a concrete saw to cut through a concrete floor, the minimum distance you can achieve, along the entire perimeter of the room, to separate it from the rest of the floor.
There is a system of creating an isolated floor which is called "floating floor". This method is extremely tedious to attempt. It really does require the assistance of a qualified PE to attempt, due to the fact that this method is essentially loading a spring to a neutral floating condition.
Doors and windows are amazingly huge holes for sound to travel through. Again, where air goes, so goes sound.
My doors are just slightly overkill for a woodshop application, but they are exterior, solid core slabs, with 1/8" sheet lead, 2 layers of 3/4" plywood/MDF, with acoustic treatment of 1" OC 703 rigid insulation and 1x hardwood for the final surface.
All doors have an adjustable threshold, with a bottom sweep that rests on the threshold, and a 2nd bottom sweep attached to the plywood. All door casings are double stop plates with neoprene gasket seals on each interior stop, and resemble a step or bank vault.
Window's are individual challenges, but the principle of how much mass you need is the same as a door; the mass should be at least equal to, or greater, than the mass/sq ft of your wall... and not allowing any air passage along the door's perimeter.
To increase the TL even further, do NOT let your interior surfaces touch at the floor, ceiling or corners. Leave at least a 1/4" gap, and caulk each gap, followed by filling the gap with 1/2" backer rod, and caulk over that. The different layers should be installed in an alternating, stepped back pattern so that the gaps actually cross over each other.
I noticed there was a link to Sound Isolation Company as a supplier of Green Glue products. While GG is a fantastic product, I cannot express my utter frustration with their acoustic caulk sold under the name of SilenSeal. The product suffers from a 50% shrinkage, poor work ability and poor manufacturing quality control. I would recommend OSI's SC-175 Acoustic Caulk. It exhibits far less shrinkage, greater work ability and the clean up is a breeze.
For my little shop, I will be integrating many of the same principles I used in the studio. Namely, gypsum between the 2x4 studs and the ceiling joists, standard pink fluffy insulation, 3/4" OSB on the stud face, followed by 5/8" FR Gypsum. I'll caulk every single hole I can find to fill.
For my floors, since my building as completely wood framed, I'll put a layer of 3 lb/sq ft mineral wool, followed by 3/4" T&G OSB sub-flooring.
10-01-2009, 11:35 AM
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