Which books OR online courses are best for Audio Industry

Pl. recommend books you feel must for Loudspeaker design building Amplifier. Also about online couses for the same. here are many on acoustics but very few on Amp & loudspeakers.
Bob Cordell has a good book on amps. Nelson Pass has a lot of great Burning Amp lectures and literature. Mr. Carlson's Lab on YouTube is great and he runs classes on Patreon. Can't tell you much about speakers. I have no desire to crack that can of worms. Way too complicated. 
Loudspeaker Design Cookbook by Vance Dickason
Testing Loudspeakers Book by Joseph D'Appolito
both available at Parts Express
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Warning, this is math heavy as it was designed for engineering students: 

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

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.
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/
Crowhurst on amp design