There is no shortage of "experts" with a wide range of opinions on the subject of sound correction. When I first started researching the science behind room treatment it was overwhelming, to save you time I tried to get the best resources and put it all in one place. Here are some of my favorites...
Absolutely NONE... Acoustic foam is completely ineffective on lower / lower mid frequencies, not to mention flammable and made in China from undisclosed toxic materials. Don't say we didn't warn you.
Depending on the severity of the issue from 15-45%. Here's how you calculate: Click here to calculate how much acoustic treatment you will need.
Sorry folks, it simply doesn't work. At best you may absorb the highest of frequencies which is great if you are trying to capture a recording of a dog whistle or even the occasional dolphin.
If you have any interest in Production, Mix Engineering, or Mastering watching Pensado's Place is a MUST
Bob Hodas of bobhodas.com teaches Dave and co. the secrets behind making your room sound the best it can be.