Light Reading 😉
Those in the hobby long enough recognize his name. Here's his website for your expanding knowledge enjoyment.
There's a ton of info on Linkwitz's site. He truly was a giant in the field of speaker design.
Another site with good reference reading is http://www.gedlee.com . There's a ton of info in the books and papers sections that are freely available. It's especially good if you want to start experimenting with waveguides - even if you stick to tweeters over compression drivers like I have.