To make one 4'x6.75' hinged baffle, you will need to construct two 2'x6.75'
baffles. First, we will construct our inner frame out of 1x4x8 SPF. The inner width once assembled should be the same as the Roxul Safe'n'Sound, or ever so slightly larger - at least 23"W. The inner height, on the other hand, will be longer than a single piece of Roxul. Mine are approximately 78"H inside, but if you want to make them taller go right ahead. I also used simple butt joints on the whole project, but feel free to use mitres if you wish.
Once you have your eight pieces cut for the inner frame of the two 2x6' baffles, begin to assemble your frames. You may either use 1 1/2" wood screws or nails - keep in mind, however, that screws will most likely need to be pre-drilled as to not crack the tips of your pieces. Another option is to use right angle brackets on the insides paired with some small 3/4" screws. Assemble your two 2x6.75' baffles.
Now we need to add an inner 23" brace to each of the frames. I placed mine at 47" as to allow one full piece of Roxul Safe'n'Sound and one partial piece per 2x6.75' frame.
Take your fabric and cut it into appropriate sized pieces. Total width of your main covering should be the outer width of your absorber, plus two inches (an inch over hang on either side for stapling). Use the same formula for the height. You will also require one piece for the rear of your absorbers to enclose the final product.
Important: When selecting your fabric, ensure that it is breathable. The best test is to put it up to your mouth with your palm on the opposite side, and breathe into the fabric as if you were going to clean your glasses (Haaaaaa). The more air you feel on the opposite side of the fabric the better. This will ensure the sound waves are making it through the fabric to your absorbtive insulation.
Attach the fabric. Place one of the frames on the floor infront of you, then a piece of fabric over top. This next part is the trickiest bit. If you staple the back side as if you are tuning a snare drum, you should have no problems. Make one staple in the top-center, then grab the bottom and pull it tight (not too tight) and staple bottom-center. Then lightly pull the left side and staple left-center, and then pull the right side tight and staple right-center. Move around the rear of the absorber in this opposite fashion to keep a constant tension around the entire thing. When you come to the corners, fold them over in a neat fashion and staple them as well.
Turn over your covered baffles (so that the fabric side is on the floor) and place a full sheet of Roxul Safe'n'Sound in each of the 23"x47" spaces. Next, measure the height of the partial space and cut your Roxul accordingly with your insulation saw. Fill the remaining space with your newly cut pieces.
Important: Never compact the insulation into tight fitting frames (pay particular attention to this when building double thick absorbers) as this is actually counter-productive and will cause a significant decrease in effectiveness. Absorbers work by the sound waves moving around particles in the insulation, which in turn converts the sound waves into heat. Remember: you can never destroy energy, only convert it to another form.
Now repeat Step 5 on the opposite side of each baffle. Once finished you have completed the inner frames of each baffle and they should be a self contained unit.
Time to add the outer edging. This not only gives the baffles a finished look, but also adds to the stability. I left mine natural SPF, but you may also use nicer wood/stains to class it up a bit. Cut your lengths to the appropriate dimensions and screw to your inner frames (thus covering over all the unattractive staples and fabric edges).
Grab your door hinges and measure an equal distance from the top and bottom and attach to both baffles.
The final step is to add two 2" rotating casters to each 2x6.75' baffle (four per hinged baffle). Once this is completed, you have finished one hinged mobile recording baffle. Stand it up and move it to your studio space - just make sure to keep the angle away from 180 degrees!