I decided to try making some base traps to see what kind of difference it would make for music and movie watching. The room we listen and watch movies was rather boomy for all low end.
I choose 8lb cotton from Bryan at sensiblesoundsolutions.com he was very helpful with my questions. The cotton comes 5" thick
24" wide and 94" long. It comes 4 pieces to a bundle. A chunk type corner was what I chose to construct so I first had to cut the cotton into 24" squares than cut corner to corner to make 4 triangles approx. 24" on one side and 16" on the other two. The traps I choose to make are 90" tall so I needed to cut 44 triangles (I guessed at 44 because I didn't know how much they would compress once I stacked them that high) for the first 2 traps. I figured I could just cut the cotton with a long razor knife, the type wall paper installers use (the blade can be extended to about 2 1/2"). It didn't make much of a mark on the cotton to my puzzled surprise. I have cut myself so many times just by bumping the blade as they are very sharp. I then decided to try different methods on one end that would be scrap. I tried a fine tooth handsaw made for wood and it did cut it with a bit of pulling on the fibers but did prove to be rather slow. I next decided to try a circular saw with a fine blade( I know this is only cotton fiber that looks like shredded up denim jeans but it is really dense, which is why it works so well I guess). I have used power tool for 30+ yrs. in furniture making so I felt comfortable you may not want to depending on your skill and comfort level. The other option I thought of which Bryan later said he used is an electric carving knife. you know the one in the back of the drawer in the kitchen that always seemed like a good idea but is almost never used. Anyway, once I had cut 44 triangles it was time to build a frame to hold them.
I started by building a triangular frame from 3/4" x 1 1/2" clear pine. It can be purchased at places like Home Depot and Lowes. I cut the front horizontal pieces 23 1/2" long (cut square on the ends) and the other sides 16 1/2" (with a 45 deg. bevel on each end.) The pictures will make this easy to understand. I then cut 3 pieces 90" long for the 3 corners. I put the front face together first with glue and 1 screw in each joint. Use plenty of yellow glue and once it's dry you can handle it with no problem.
After the face is together(you don't have to wait for the glue to set) turn it face down and add the angled pieces flush with the outside edges. If you have ever seen a roof on a building get framed its the same process you are just using tiny rafters and ridge beam.(again the pictures will make more sense of this. Once these were together I let them set over night for the glue to cure.
I stapled a piece of plastic hardware cloth (screen with large holes) on top of the bottom horizontal frame members to support the cotton. Because the cotton does shed a little (although it's not a hazard as fiberglass could be) I chose to wrap the complete chunk before putting it in the frame. I used a material called septic paper. It is used for covering stones in a leech bed of a septic system before the stone is covered with dirt. It is very sheer and tough. I looks like gardeners shade cloth but very fine. It too can be purchased at HD and Lowes for about .03 a sq ft and comes 2',3'and 4'wide. I laid it on a drop cloth and sprayed 3M #77 adhesive on it then set the cotton triangles on it with the 24"face down. I also sprayed a bit on the cotton to hold each piece to the next. Then wrapped the septic paper around it sticking it to the cotton with #77. Then it was a matter of sliding it into the frame. You just need to wiggle it a bit at a time. When most of it is in you can stand it up and gravity will help with the rest. I have not covered them with fabric yet because I spent time this week experimenting with how much reflective surface I wanted to put on the face toward the room.
This is not difficult just takes some patience. If your ability to cut pieces of wood smooth and clean is a problem you can use construction adhesive in a tube instead of yellow glue and it will fill the joints that don't quite fit right as you assemble the frame. You will need to let the construction adhesive set longer than yellow glue, you will know because when you touch it it is hard. Once it's covered with fabric know one will know what it looks like underneath.
I hope I didn't make this to confusing. The pictures are at a yahoo site. I hope the link works. If not I will try another way to link them.
I now have to go cross off a few thing on my weekend honey do list but I will post later what a difference they made It was quite surprising.

Brad

http://pg.photos.yahoo.com/ph/brock24252425/album?.dir=a581&.src=ph&store=&prodid=&.done=http%3a//pg.photos.yahoo.com/ph/brock24252425/my_photos

Did you try the method used for cutting fiberglass? It involves putting one piece of wood ( ie 1x2 or 2x4) lined up under where the cut will be, and one lined up over the cut, then pressing them together and cutting along the edge of the wood where it's pinched thin. Makes for very quick work, and one cut usually does it.

Nice job, Brad, I look forward to your comments on its performance.

Wow, great job. Did you cover the entire trap with any fabric or leave them as they are in the photo?

Thanks Kevin,

I covered them with a cotton fabric similar to the wall color. I also changed the grill cloth on sides and rear to blend in with the walls to please my better half. She was not convinced but most people that come in the room don't really notice them until they are pointed out.

Brad

I've built them. It was a real PIA, so i bought some of these corner bass traps.

http://www.gikacoustics.com/product_info.html#5