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In the Forum: Horn-Loaded Speakers
In the Thread: Phase plug for midbass
Post Subject: Make it hard for yourself!Posted by jessie.dazzle on: 9/30/2007
Hello Malinowski,
Sounds like you may already have the necessary experience in working with plaster, but in case you're not used to making anything this large:
For the final horns, especially if they are large, use hard modeling plaster. My upper-bass horns are cast, which is what you are planning to do. Over here I use a plaster conceived for use in the making of molds which must withstand high temperatures... it is in effect a refractory material, called "Molda Dure", mixed close to 2 parts solid to 1 part liquid (see link to data sheet)... it should be thick but still "pourable". (Nobody stocks the stuff... I have to order it special).
If you can work some hemp fiber into the mold before pouring, it will help strengthen the final result, but more interestingly, if you use enough, it will really help deaden or damp the horn so it doesn't ring.
If you use normal plaster, and don't mix it "stiff" enough, you will end up with fragile horns, the edges of which are likely to crush under the horns own weight (we are talking about a large and massive horn here)... This of course is fine for making prototypes, as they can more easily be smashed into small pieces and carted out to the dumpster.
Good luck... Your first purchase should be one of those weight lifter's belts!
jd*
Link to data sheet :
http://www.bpbformula.com/PDF/EN/MOLDADUR-ENGLISH.PDFRerurn to Romy the Cat's Site