2 Sound measurement
Although you're familiar by now with elastic bands (and plastic ducks!), you may not be quite so familiar with the terminology and figures used when measuring sound. Be aware though, that, as mentioned at the end of the previous section, with regard to human hearing, all figures given are approximate, since the absolutes vary from person to person, and hearing normally deteriorates with age and with any continued exposure to high sound levels (see Section 16, Safety). The human ear is sensitive to changes in loudness (level) but is more sensitive to changes in level within a specific range of frequencies – those covered by the voice.
Hertz – Hz, is the SI unit representing the frequency of sound in cycles per second. ...