16.1 - Sound

Along with light, sound is one of the most important ways in which we experience the world. For most people, sound is a fundamental part of every moment. You might not hear the terms frequency and amplitude in everyday conversation but almost everyone knows these same properties by the names low and high pitch and loudness. For example, musical notes are different frequencies of sound. This section describes the basic properties of sound and how we perceive and understand voices and music. Read the text aloud
Basic properties of sound
Sound is a longitudinal wave, like the compression wave on a Slinky™ spring. Sound waves are similar except that they are much higher frequency and it is air that is being alternately compressed and expanded rather than the coils of a spring. Read the text aloud
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We perceive different frequencies as having different pitch. The lowest frequency humans can ordinarily hear is a deep hum at a frequency around 20 Hz. Even this frequency is so fast that you cannot see the vibration with your eye; instead, you can only see a slight blur. The highest frequency that a young, healthy human ear can ordinarily perceive is a high-pitched whine at a frequency near 20,000 Hz. Read the text aloud Show Age and species effects
We also perceive sound to have a loudness. The loudness of a sound depends on the amplitude of the wave. A loud sound has a larger amplitude than a soft sound of the same frequency. A stereo’s speaker moves back and forth a greater distance when producing a loud sound than when producing a soft sound. The larger amplitude of the speaker’s motion causes larger amplitude pressure variations in the air. Read the text aloud
Example of a frequency spectrumAlmost all sound you hear contains many simultaneous frequencies at once. Even a “clean” musical instrument sound contains a dominant frequency, called the fundamental, and many overtones, which are additional frequencies that give the sound its characteristic “piano-ness” or “guitar-ness.” The fundamental frequency is also called the first harmonic; the higher frequency overtones are called the second harmonic, third harmonic, and so on. The graph on the right is a frequency spectrum, which shows a range of frequencies up to around 2,500 Hz with the loudest peaks at 400, 800,
1,600, and 2,000 Hz. Read the text aloud Show Harmonics and overtones
A dog whistle is used to train dogs. It gets the attention of dogs but is silent to humans. Why is this? Show

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