Which books OR online courses are best for Audio Industry

well, there are several books and also websites containing materials for audio learning course. In that context selection of proper study materials is an important matter. However being a music educator I can suggest you the portal of eduhelphub.com where the experts are always ready to help students to be enriched with audio learning and knowledge.

Crowhurst on amp design

I found this course online by university of Rochester on Coursera a free course and If want certificate pay $49. Any thing like this courses offered by Universities? https://www.coursera.org/learn/audio-engineering/

As an introductory primer on tube amp design, you can watch the You Tube video of Roger Modjeski’s (Music Reference) 90 minute talk at the 2015 Burning Amp Festival. It’s free! Also on You Tube are videos posted by Roger himself, wherein he discusses pre-amp design.

Merlin Blencowe and Morgan Jones have fantastic books on amplfier design (tubes/valves).

Warning, this is math heavy as it was designed for engineering students: 


https://amzn.to/2ICQgaV

Loudspeaker Design Cookbook by Vance Dickason
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Testing Loudspeakers Book by Joseph D'Appolito
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both available at Parts Express