Since Siegfried Linkwitz was mentioned above, here is his site, one of monumental importance to audiophiles (IMO).
There's advice about speaker building as well as construction plans for outstanding speakers (I heard the Orions II—to say I was blown away is saying too little)
There's advice about speaker building as well as construction plans for outstanding speakers (I heard the Orions II—to say I was blown away is saying too little)