When equalizing vocals, much of the work involves removing offending frequencies. We do so by cutting out a narrow band of frequencies.
Typical recommendations are:
- If there is too much low frequency rumble, cut down on frequencies below 80 Hz.
- If the vocals are booming, look for an equalizer that can put a magnitude reducing notch with a middle frequency somewhere between 100 Hz and 300 Hz, dipping down to, say, -30 dB, and a width at -3 dB of probably about 100 Hz. You would have to experiment by moving the notch up and down the interval between 100 Hz and 300 Hz to find the offending frequency band.