[personalcompute]

For #1 I can highly recommend this interactive article by Bartosz Ciechanowski: https://ciechanow.ski/sound/. It might lack the depth you want in intermediate or advanced topics, but in my opinion it is the most efficient and effective beginner education material out there.

[rramadass]

Nice site; the interaction aspect is particularly good.

Thanks for the link!

I also found this "University of Southampton" site on Sound really helpful : https://blog.soton.ac.uk/soundwaves/