Humans cannot hear every sound. Our hearing is not sensitive to all frequencies: it simply doesn’t pick up very low or very high tones. If a vibration is too soft we don’t hear it either.
Our ability to hear sounds also changes with age. A healthy twenty-five-year-old man or woman has a far greater range of hearing than a fifty-five-year-old. Generally, as we age we hear increasingly fewer high tones and find it more and more difficult to pick up soft sounds.
High and low tones
The level of a tone is determined by the speed of the vibration. More specifically: the faster the source of the sound vibrates, the higher the tone sounds. We call the vibration speed the frequency. A source of sound that vibrates a hundred times per second has a frequency of 100 hertz (Hz for short, the official unit used to express frequency). Our hearing range for low and high frequencies is approximately 20 Hz to 20,000 Hz. Our hearing has a low to high frequency range of almost ten octaves.
Loud and soft sounds
We express the strength of sound in decibels (dB). Sound we can barely pick up – very soft sound – is established as 0 dB.
The following approximations also apply:
- 0 dB = hearing threshold
- 40 dB = whispering
- 60 dB = talking
- 80 dB = screaming
- 90 dB = busy pub
- 100 dB = disco
- 120 dB = pain threshold