For example... for me, it usually starts with a doodle. Sometimes I have a particular driver in mind when I start sketching, but it's almost always a sketch on paper with pencil that gets the whole ball rolling.
On almost all of my speaker and sub builds, I started with a quick sketch... which I tweak and recreate from different angles changing a few angles/shapes here or there until it starts to look promising. Usually one or more of those mini-sketches has an angle -- or in my case -- a curve that looks especially promising to me. I then continue with the sketches trying to bring out the beauty in that particular shape... getting proportions dialed-in, altering curves to attenuate one part or another, and generally refining the shape. Usually, a few brief 5-10 minute sessions (with breaks in between from a few hours to a few days) is all I need to get the look mostly there.
Here is a 'sketch page' that shows how a few doodles ended up turning into a shape that eventually became the Cello's speakers I entered in the 2012 MWAF. That one circled drawing in the bottom right really jumped out at me as having a nice curve and look to it. It's fun looking back at this to see what ideas did, and didn't make it into the final design.
Then I often start plugging dimensions into BassBox Pro to get a sense of the inner cabinet dimensions in liters of volume to see what size and scale I'm looking at for a cabinet height.
Then I usually make a full-size mock-up of the shape and see how it looks in the flesh. For really complicated cabinets, I sometimes make a small version to see if it's even feasible to construct the thing.
For my last build, the Summer Winds... I made full size front- and side-views to scale, and then measured right from the drawings to make my panels... that made construction really easy. I drew notes on those drawings of various sizes of braces, distances, angles, thicknesses of wood, etc. Basically all the information I would need to build a set of those cabinets would be on those two drawings. I use brown floor underlayment rolls from Home Depot for that. It's cheap and comes in pretty big rolls; looks like a paper bag for the most part, but lighter.
Once I got basic volumes figured out with rough sizes, I took this paper to work for a few months and drew up some dimensions and figured out how to assemble/cut/trim pieces on my lunch break... it was a really fun diversion from work at times, I can tell you.
I was curious as to how others' got their speakers from 'idea-stage' to 'ready-for-construction' and thought it might be something worth reading for some of the newer speaker builder/designers as well.
TomZ