golden Ratios are not a good way of knowing if your going to have good or bad sound

there are too many variables

in this calculations you take for granted that all modes will be exited and in the same degree and that the listener will here all these modes

this is far from reality since the speaker are not set in the 3 way corners and the listener ears are not in the corners were all modes interact

second your room is not a perfect rectangle and does not have perfect reflecting surface so the distribution is far from being as in sou ch papers

it is allot more important to place the speaker correctly and too have good acoustic treatment diffusion and absorption in the correct places

ti dome you should buy Floyd Toole book Sound Reproduction is has a lot more knowledge probably more than your contractor and it is an easy read

the sdec 4000 is an incredible tool specially if it is used as a finishing touch