What sounds can we hear?

We hear many sound frequencies, from the shrill notes of bird song to the deep growl of traffic. But, because of the way our ears work, we do not hear all of the sounds around us. Our ears pick up frequencies from about 20 to 20,000 Hz (Hertz, vibrations per second). We hear sounds below 80 Hz as low, deep booms, thuds or rumbles. Frequencies below about 30 Hz may not be heard clearly, but if they are powerful enough, we can feel them as vibrations in the air and ground. Our ears are most sensitive in the range from 400 to 4,000 Hz. (Human speech tends to be around 300-1,000 Hz.) Sounds above about 5,000 Hz are extremely high-pitched squeaks, hisses and screeches. As people get older, their ears become less sensitive to high notes. So a young person can hear a bat's very high-pitched squeaks, while an older person cannot. (World of Science)