Center each closet flange on each of the wood squares. Run a full bead of silicone caulk around the base of the flange and use four screws on each flange to attach it to the boards. Wipe away any excess caulking and put the assemblies aside to let the caulk dry.
Calculate the length of ABS pipe needed. Your speaker stands should allow your speakers to clear any obstacles, placing the tweeters level with or slightly above your ears, if you are using the speakers as recording monitors. Do not forget to add two inches to account for the wood supports on the top and bottom of the completed stands. Cut the ABS pipe with the hacksaw.
Glue one flange to each ABS pipe using the ABS cement. Let it dry as directed in the cement instructions before filling each pipe with sand. Attach the tops using cement, and before it sets, place the stands on their sides to align the tops and bottoms. When the cement sets, your stands are ready for use.