title_body: Does using two paper filters in a drip machine strengthen flavour?
upvoted_answer: Yes, because it allows more time for coffee to be extracted as it stored in a longer time for coffee to drip. However, other parameters also have effect regarding this issue (such as, type of bean, roasting profile, temperature, brewing method)
  But using double filter since it also filter the "flavor", making it stale (you may lose the pleasant acidic, fruity flavor, or other unique flavor your bean may offered) and double filter can make your coffee over extracted thus unpleasant bitter flavor. 
  If you want your coffee strong you may want other experiment
  
  
  Use fresh coffee bean
  the older the coffee, they tend to lose their flavor. The fresher, the better. You have to store your bean properly too, keep it in air-tight container, avoid direct sunlight
  wait  to grind your bean, until the last minute coffee lose a bit of its flavor after grinding. Ground coffee is also more sensitive to the moisture
  Use different kind of bean You may use robusta, it naturally has more "caffeine" compared to Arabica, therefore can "hit" you harder
  Use different kind of roasting profile the darker the roast, the bitter it is, but it has less caffeine.
  
  
  
  
  when brewing
  
  
  Pre-warming the equipment or insulating it basically the hotter the temperature you get bitter flavor, to avoid the "upleasant bitter" you may adjust the water temperature according to your preferences. Temperature loss often occurs as a result of heat absorption by the equipment itself (and therefore stale flavor), so pre-heat the equipment would prevent it
  Use finer grind Coarser grind can make your coffee under extracted
  Adjust the amount of your coffee
  Adjust the steeping time
  
  
  In the end it comes down to your preference(s). No single technique is right for everyone. Enjoy your coffee immediately after brewing
  
  My explanation might not answer your question directly, double filter affect your coffee, yes it is. But other factors simply can be neglected