Instruct the male vocalist to sing a few bars into the microphone. Listen to the vocals for noticeable audio problems, like popping, nasally sounding vocals or a flat overall sound coming from the speakers.
Examine the equalization settings on your mixing board. Most mixing boards have a three-band EQ built into the board. Depending on your specific mixing board, this can include frequencies ranging from 30Hz to upwards of 18,000kHz. The human voice ranges from about 200Hz to 1000Hz. According to HomeTracked.com, the average male voice is between 125Hz and 180Hz.
Set all EQ knobs to "0." Leave all frequency knobs at 75Hz and below at "0." Boosting frequencies below that will only muddy the singer's vocals coming through the speakers.
Turn up the EQ knobs between 200Hz and 1000Hz to brighten up the vocals. This is particularly helpful when dealing with nasally or deep singers. Turn down the same frequency knobs to dull higher pitched voices.
Reduce frequencies in the 1kHz range to remove popping and hissing from the microphone.