The inside diameter of these tube traps is 12″. The outside diameter is close to 15″. The width of the fiberglass is 1″. They come in 3 foot sections and must be purchased from an insulation distributer; a company that sells to contract HVAC companies. It’s pipe insulation and it’s compressed fiberglass covered in a paper wrap. You can use any diameter. As you know, the lower the Hz the longer the waveform. The bigger the ID the lower the frequency absorption capabilities of your tube traps. There is a good deal of science involved!
I got a 4 foot by 8 foot, 2″ thick styrofoam sheet from Lowes to make the inset “sandwiches” and internal support pieces. You will need 4 per tube trap. 1 for top, 1 for bottom and 2 glued for the middle connection point “sandwich”. These are roughly the circular size of the ID. Get a box of general construction liquid nails for all gluing.
You will open the paper that covers the pipe insulation and glue the seam closed. The resealable paper is helpful to close this up as the glue dries.
Once all 3 foot pieces are glued and dry, glue the middle support styro pieces together. These support “sandwiches” are used to join the 3 foot sections of pipe. Add glue to the inside of the bottom pipe where this support will go. Poke long nails into the sides of this so that it won’t slip down into the bottom section when the glue is still wet. 5 spaced, removable nails work great.
Once all has dried, remove the support nails and add glue to the top edge of bottom pipe section and the styro sandwich where the top pipe section will join. Add the top section of pipe. Allow to dry. Now you have a 6 foot section of pipe. DO NOT glue the top and bottom “caps” on yet. I then used a razor blade to cut the insulation’s paper “jacket” length-ways top to botton creating essentially a half jacket for the trap. This creates a side (back) that is more diffusive and one side (front) that is more absorptive. Use masking tape to keep this jacket in place as it will be flappy or even fall off without the tape. Tape it lengthwise to hold the jacket seam tot he compressed fiber.
Covering the tube trap is another beast in of itself. The fabric that I used is Guilford of Maine fabric which is acoustically transparent. There are many colors available. You will need about 8 foot lengths of material per trap. You will need to use a fabric measuring tape to measure the finished outside diameter for the tube trap. Measure and tack your material adding about .75 inch for slack as you will be sliding this over the tube like a sock and will need some wiggle room. Have somone who knows how to sew, sew your “sock”.
Cut off the access material with about 6 inches of excess beyond the seam. Turn it inside out and inch your sock down the tube trap. Once you have reached the end keep going until you have about 1 foot of excess material top and bottom. Fold this excess material into the top and bottom of the tube and add glue to the inside of the pipe, on the material. Then add the end caps. Allow to dry.
Curious as to what frequencies your tube traps will be effect to? There are calculation you can do to find this info. Easier than that though is to gently drum on the sealed and finished sections of the trap. The resonant frequency your hear if the fundamental Hz of your trap. This is the lowest frequency your trap is most effective absorbing. Enjoy!