Male voices generally fall between the 85 Hz and 155 Hz frequency ranges, female voices fall between the 165 Hz and 255 Hz frequency ranges, and children typically range from 250 Hz to 300 Hz.
If the noise you are trying to absorb is common human speech like that found in an office, classroom, or basement setting, then performance in this Common Vocal Range (identified here as an average of 125 Hz, 250 Hz, and 500 Hz), is most important.