Thursday, July 07, 2005

Building a soundproof fence (Soundproofing a fence)

In recent weeks we have been bombarded with questions on how to soundproof a backyard fence, (must be a summertime thing) so I figured I'd post a little note on soundproof fences...
Generally the best soundproofing fences are what is known as septum fences. What is a septum fence? A septum fence is a fence that is constructed with cedar or redwood slats or even a fiberglass slats/panels, the difference is that there are slats on both sides of the fence with a soundproof barrier or membrane insert in the the center between the the slats themselves. The soundproof membrane is generally made up of a combination of materials such as mass loaded vinyl and closed cell foam mat. The MLV acts as a reflective barrier and the closed cell foam is the absorbent part of the septum membrane. Remember that with any soundproof fence, the fence itself must be at least 8' above the noise source to work properly. For example, it traffic is your noise source,then the fence needs to be at least 8 above the tires or exhaust of the cars. If the car stereo is the source, then the fence must be 8' above the car speakers in order to be effective. If the fence is to built atop of a berm, then the berm height can be added to the 8' total needed for good soundproofing. So, if the city has a 6' fence height ordinance, then the berm and a 6' high fence would be the ticket.
Now here's a breakdown on how to construct this type of fence from scratch. You would construct the frame with the 4" X4" anchoring posts that are usually spaced 6 to 8' apart. The cross members will most likely be 2' X 4' s. Now you will nail up the slats on the inside (backyard side) of the fence. These slats need to be butted as tightly together as possible. Caulking between these slats is always a good idea. Next we'll begin working on the cavities of the fence that are facing the noise source (basketball court, traffic etc.) First you will staple or glue up a layer of MLV (mass loaded vinyl) to the inner cavity areas. We have had the best luck with the 2Lb MLV, but the 1 Lb will work fine as well. You'll need to caulk the seams of the MLV as well as the entire perimeter. Sealing the MLV is imperative. The next step is to tape the caulked MLV seams with a quality seam tape. Time for a lemonade break.... Whew, it's sure hot out here!!
Now we are ready for the closed cell foam (America mat) this mat is glued directly to the MLV layer making sure that the foam mat covers the entire face of the MLV. There are 2 sides to the America mat, one is pebbly and the other is smooth, you'll glue the smooth side to the vinyl. The pebbly side is the side that absorbs the sound and needs to face the noise source. Once the foam is glued to the MLV (using 3M-77 or 3M-80, or any good weather resistant contact cement etc.) Remember to use the acoustical caulk to seal the edges of the foam mat in areas where it contacts the fence structure. Now you are ready for your final layer of slats. The backing slats should have a small gap between each slat to allow the septum to absorb and block the sound. The gaps should be anywhere between 1/4" to 1/2" in width. The closed cell foam is black and very weather resistant, so it will hold up well in the elements.
Now if your new fence is at least 8' above the noise source it will be work well but if the height of the fence is less than 8' then it will naturally be less effective at blocking and absorbing noise. Outdoor noise is much like a bubble or large wave of water, it will always look for the least path of resistance, so if the fence is too low, guess where that least path is?
Just a quick note, masonary, brick, and stone fences are excellent soundproofers, but their cost is oft times prohibative, the sepum fence is a great alternative to a masonry fence.
Thanks for reading and learning together.

As Always,

Dr. Bob
e-mail: dr.bob@soundproofingamerica.com
Call Toll free (877) 530-0139

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