[LAU] Measuring the acoustical characteristics of my studio using FLOSS software?

Hi! I'm in the midst of trying to treat my room acoustically, and I really want to do measurements of my room acoustically. Of course, I know way too little about this, and therefore, I need your help as always! ;) (if you reply to this e-mail, imagine I'm 5 years old when you explain stuff). So, what I have is this: - A set of studio monitors (Adam A3X) - A microphone (Senheiser MK4) - A room... - My studio computer with Linux What I want to do, roughly, is this: - Through a test tone(? test sound?) measure the frequency "response" of the room. I want to get a nice curve, like an equalizer, which tells me roughly how my room responds to the different frequencies. - I want to do this before and after I apply treatment. So, my question is: How on earth do I do this?! Are there FLOSS tools available for this? Is it easy to do something as basic as this? Best wishes, zth/Gabriel