Good article on the electrical theory of pickups. I have used very similar models for my pSpice analysis of pickups over the years. www.buildyourguitar.com/resources/lemme/
Introduction to Sound Recording A good one on the theory of many things electronic and musical. Thanks to ashcatlt for finding this one. www.tonmeister.ca/main/textbook/
It's not a bad work overall, but does have some "homemade" information therein. For instance, regarding "Watt's Law" on electrical power....."Watt's law is an improper name used for the Basic Power Formula", en.wikipedia.org/wiki/Watt%27s_Law