"Building a helmholz trap is like EQing the room... "
Your RIGHT!
But the problem with most small rooms is there are problems throughout the spectrum and building helmholtz resonators for all problem areas would be pretty darn hard (plus there would not be to much room for you equipment left
). The best thing to do is use rigid fiberglass or mineral wool in as many corners as possible and at that point you could follow up with a tuned trap as to put "icing on the cake" of tuning the room.
Glenn