For #1 there are a couple great youtube channels that cover a lot of the technical background on drivers and control systems (amplifiers) as well how to objecti

For #1 there are a couple great youtube channels that cover a lot of the technical background on drivers and control systems (amplifiers) as well how to objectively compare and test audio setups. 1 - PS audio https://youtube.com/c/PSAudiochannel https://youtube.com/c/PSAudiochannel and 2 - Tech Ingredients https://youtube.com/c/TechIngredients https://youtube.com/c/TechIngredients In this tech Ingredients video they go over some really well performing but very simple and low cost to make speaker and amp set, as well as a test setup to do objective comparison tests on different designs. https://youtu.be/GslJ8Hf4WwE https://youtu.be/GslJ8Hf4WwE For #2 I've actually done quite a bit of work with sound and the body, in designing medical devices. It's interesting, sound travels very well through the body, why bone conduction headphones and ultrasound work so well. Most of the good info on sound and it's interaction with the body I've found to be in clinical and scientific papers. I hope something here helps!