I find a zillion reference books on Amazon. However, there are a few that are more highly regarded than others.
Testing Loudspeakers- Joseph D'Appolito - still considered a standard reference book with regards to the practice of testing loudspeakers to get their basic parameters.
Loudspeaker Design Cookbook - Vance Dickason - a good reference guide for those new to loudspeaker design - it provides basic info regarding all the major steps in a build, and you can google your way thru more details on any of these topics.
So, I will purchase those 2 if/when I get the measurement jigs/mic/software all working to my satisfaction.