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heres how you do it:
1) find the dimentions for the cutout diameter and overall speaker diameter.
2) add an inch or so to the "overall" diameter. if its a 12" speaker, the inside cutout will be 11", the outised diameter will be 12", and the added inch will make 13".
3) make two rings. both will have outside dimentions of 13", but one will have an inner diameter of 11" (this one will hold the speaker), and the other will have an inside diamteter of 12" (this will surround the speaker).
4) for the surround ring, save the inner scrap piece.
5) round off the edges of the surround (13/12) ring. this will prevent the cloth from being torn, and will make the finished product smoother.
6) center and clamp both rings together and secure them with wood glue and recessed wood screws to form a bond. lay the center scrap piece in place. invert the sub and drill mounting holes for the speaker through the scrap piece and the 13/11 ring that will hold the speaker. put a dark tic mark so you can line the pieces up later.
7) cover the center scrap piece with aluminium foil.
8) after positioning the rings where you want them, stretch the cloth over the combined ring pieces. then take the scrap center piece and "stuff" it into the center cutout. if you can make out the tic mark, this should help you line up the screw holes. if not, you should have a good idea of how it fits based on how you positioned the ring. you only need to but 2-3 screws in. secure the scrap piece into place, and then glass over it all.
9) after a couple layers, remove the center scrap piece. you can now see the main form. continue glassing like normal.
as a side note, you will be filling the inside diameter where the "donught" where the speaker will drop into place. it might be a good idea to leave a 1/4" extra opening (i.e., 13.25" outside dimention, 12.25" inside dimention). that will give you enough room for a bit of bondo, fiberglass seepage, and covering material.
edit: i got a little carried away with my number keys, lol. i dont recommend making a 113" diameter cutout, or installing a 122" sub finger spasms.
:shhh: i do cocaine :/shhh:
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