I have a small room - Length:5.5ft, Width:2.5ft, Height:6ft, where i do most of the vocal productions for ADRs and cover songs etc.
The room walls are 4inc brick walls on top of it i have a layer of glass fibre (4inch) and on top of it i have a layer of 1/2 inch gypsom board with cavities. all together this gives moderate absorption and isolation and i am happy with it. i havent done anything on the ceiling but have a 2inch think foam diffuser of 1ftx2ft pasted at the center of the 4inch concrete roof and this reduced much of the reflections caused by low-ceiling. Floor has a rubber mat to cover whole area.
In most cases my recording are ok(more luck with female voices) but with male voices the takes are not that good. some high frequency boosting/rings are heard and some metallic kind of tonal change happens some time.
I have a 21inch LCD on the wall which is directly behind the MX440 i use and it could be causing some reflection i guess and i am planning to put a foam panel behind the mic.
I am here to get some suggestions and inputs for betterment of the iso room so that i can have improvements in my recordings.