When a speaker does not sound right, how do you know which part is wrong?

I bought Polk LS50 from craigslist for my kids. One speaker produces some static noise and it sounds much weaker than the other.

It has one 1" dome tweeter and two 6 1/2" drivers. How can you test which went wrong? Tweeter, driver, or crossover? Or, something else? Is there a way to tell what went wrong by just listening to the sound?