Eberhard Sengpiel was a two times grammy awarded sound engineer. Until to his death a few years ago, he shared his seemingly endless knowledge on his website. The site is now taken care of by his son.

It is not a course, a lesson, no videos and such. It is explaining everything that has to do with sound in general. And I really mean everything. From "what is sound", over "how to measure" to most complex things like "Calculation of the Speed of Sound in Air and the effective Temperature"

If you ever stumble over a term that you are unsure of, just look at his site and you will be enlightened. I use that website as my first and foremost source of knowledge.

Maybe it helps you as well.

Homepage is in German, but all subpages exist in English as well: http://www.sengpielaudio.com
Searchpage: http://www.sengpielaudio.com/Searchengine.htm