John Watkinson 
The Art of Sound Reproduction [PDF ebook] 

Designed to make life a little easier by providing all the theoretical background necessary to understand sound reproduction, backed up with practical examples. Specialist terms – both musical and physical – are defined as they occur and plain English is used throughout. Analog and digital audio are considered as alternatives, and the advantages of both are stressed.
Audio is only as good as the transducers employed, and consequently microphone and loudspeaker technology also feature heavily – making this the most comprehensive, up-to-date text currently available on all aspects of sound reproduction.