How many acoustic panels do I need in my room?
A: Ideally You hire a professional acoustician like Bob Hodas to tell you exactly what your room needs, for the rest of us on a budget… start with a DIY Basic Room Acoustic Measurement with acoustic analysis software like Freeware Room EQ Wizard (Win, Mac and Linux) or Fuzzmeasure (Mac, costing $150). After you determine trouble spots then you can compensate with acoustic panels and bass traps.
Ignore any online room acoustics analysis calculators, because it is impossible to account for all the variables in your specific room. This is an art AND a science. There IS NO ONE RIGHT ANSWER.