wait are you doing this blind without measurements? @mjjw
This video is timely - Acoustic Treatment: The Strategy for Small Studios
Yes it is for studios but the general comments are very much what you need to get familiar with. But for the love of all things good, get a calibrated mic. This should do - miniDSP UMIK-2 - USB Reference Measurement Microphone
Also, please talk to GIK. Room treatment is a science and should be treated so.