if you persist with the meter/RTA method, I suggest you use warble tones for the source
and an analog meter representation (meter/bargraph/whatever), not numeric.
Narrow resonances are more readily identified (often not worth trying to eq, but they can affect
the RTA 1/3 octave filter which averages the in-band spectrum).

Eventually, you might consider something like REW (can be a bit complicated, but it's also free).
Something that uses a swept tone, or MLSSA-like signal can be very helpful. There are many
products and end-to-end systems available (from near zero cost, to many thousands).