How you hear
Sound waves in the air are collected by the auricle and passed down the external auditory canal to the eardrum making it vibrate. These vibrations are then transmitted across the middle ear by the ossicles into the fluids of the inner ear. This moves the inner hair cells, which in turn activate the auditory nerve. The nerve impulses are transmitted to the brain along the auditory nerve.
Sound
Sound waves are characterised by their frequency (pitch) and amplitude (loudness or intensity).
Figure 2 - Sound wave
Higher frequencies are perceived as high-pitched sounds and vice versa for lower frequencies. Loud sounds have high amplitude and quiet sounds have low amplitude.
Frequency is measured in Hertz (Hz) and amplitude is measured in decibels (dB).
| Approximate loudness of common sounds | In dBs |
|---|---|
| Whisper | 30dB |
| Normal conversation | Up to 60dB |
| Loud shout at 1 metre | 85dB |
| Lawnmower | 90dB |
| Pneumatic drill | 100dB |
| Gunshot | 140dB |
It should be noted that, although a loud shout has a level of about 85 dB at a distance of one metre, the maximum shout, which can be sustained for more than a few words, is about 90 dB.
Human ears detect sounds in the frequency range of approximately 20Hz to 20kHz but most information in speech is contained in the frequency range of approximately 500Hz to 4kHz.
