The Yamaha Sound Reinforcement Handbook
This is basically the soundman's bible. Sold for an aspiring live sound engineer, has much more than just advice for live sound guys - covering everything from microphones to acoustics to basic electronics to handy rules of thumb to MIDI, all written to be relentlessly pragmatic. It even has a handy appendix covering logarithms.
This isn't the book to give you the final "20%" of knowledge on anything it covers - but it will help you on your way to the first 80% a lot more quickly than most other writing on anything related to semi/pro audio, and pretty much every expert in the field is at least familiar with it, if they don't own a copy.
There seem to be plenty of people interested in music and audio around here, so hopefully someone finds the unusual reference useful.