Our most sensitive hearing is in the range of frequencies that speech sounds are produced.
Of course we don‰t hear each frequency equally well. The lower and higher frequencies require progressively louder sounds for us to hear. Our best hearing range for pitches is from around 400 Hz to about 5000 Hz.
Happily, this is the same range at which speech sounds are generated! Were this not so we might all have to talk much louder to be understood.
As we are all aware, speech sounds are divided into two groups--vowels, and consonants. But what we often don‰t think of is that as a group, vowels are low frequency sounds (extending a little above 1000 Hz); and consonants are high frequency sounds, (extending only a little below 1000 Hz).
What makes this significant, is that consonants, taken as a group, are more important than vowels for speech intelligibility.