For the folded horn builders a great source for curved surfaces to be used at the end of the folds is cardboard tubing. For tight corners the tubes used for carpet rolls is a good source. For the larger folds closer to the mouth of the horn the tubes you can get at a building supply for casting concrete piers for foundations works great. It comes in a number of diameters and is easier to work with than cutting angled pieces of 3/4" MDF. The empty space behind the curve can be filled with sand through a hole after construction and gluing. This will also cut down problems with standing waves better and easier than angled flat boards. To further defeat standing waves at a low price use the small diameter bubble - bubble wrap attached with a good spray adhesive. $10 can get you a fairly large roll and it works well in boxes too. Attaching the bubble wrap to a foam or other good sound insulation product you can get the benifits of some very pricy products at a fraction of the cost. DIY means making use of anything that can do the job of a high priced commercial product using easy to find items at a budget price. Give up those secrets guys!