The 7th edition is now expanded! The LDC includes Klippel analysis of drivers, a new chapter on loudspeaker voicing which details how to tweak a completed loudspeaker design. This edition includes advice on testing and crossover changes, and an updated chapter on loudspeaker CAD software.
This book is a good guide to building your own loudspeakers, but it does have a few problems. 1:It is a bit complex and wordy, It gets a bit too technical if you don't already have experience building speakers or an electrical engineering background. 2: The graphs often have many things going on they are small and hard to read, sometimes their is no key, sometimes the scale seems to be off. Also often there are so many you will be flipping back several pages to find the graph he is talking about. 3: There is little information on active crossovers, definitely not enough to learn how to build your own amp if you want to do that. 4: He relies on a lot of software and testing equipment most people don't have and can't afford. 5: This book is from 2006 and a bit outdated. The software section probably barely applies to modern systems.
If you ignore the software aspects and get to the basics of what he is saying then there is a lot of good useful information here. The tools and testing equipment can be quite useful, but you should probably build a few systems before purchasing them. If you are a pure beginner you probably want to reference a different book first, and come back to this one later.
A fairly good overview of a 3 different speakers box geometries (notably biased toward TL's). Good sections on damping as well as cross-overs.
Seems like it was a bit advanced for me- this is my first book on speaker design, but I was able to mill through it with some basic knowledge of electronic filters and physics.