Characteristics of sound
Sounds differ in three properties. 1) Loudness depends on the amplitude of vibration — the greatest displacement: the larger the amplitude, the louder the sound. Loudness is measured in decibels (dB): hearing threshold 0 dB, whisper about 30 dB, quiet conversation about 40 dB, a noisy street 80 dB, near an aircraft 110–120 dB; the pain threshold is about 130 dB. 2) Pitch (deep or high) depends on frequency: a larger frequency means a higher-pitched sound, a smaller one a lower sound. A tighter or shorter string has a higher frequency. A man’s voice contains frequencies of about 100–7000 Hz, a woman’s 200–9000 Hz. 3) Timbre is the “colour” of a sound: a sound is not of a single frequency but consists of a fundamental tone (the lowest frequency) and its overtones; the number and strength of the overtones determine the timbre, which is why we can tell the same note on a doira and a violin. Male voices are bass, baritone and tenor; female voices soprano, mezzo-soprano and contralto. Do–re–mi–fa–sol–la–si are musical tones.
Experiment: fill identical glasses with different amounts of water, tap gently with a spoon and compare pitch — more water gives a lower tone. Tap lightly and harder to compare loudness. Safety: use plastic or sturdy cups instead of thin glass and do not hit hard; do not make very loud noises and protect your ears.