In this experiment the PC-interface cable is connected directly to the speaker, and is used to convert my voice into an electrical signal. A speaker uses electrical energy to create mechanical vibrations. These vibrations create variations in air pressure, called sound waves, that allow one's ears to feel air pressure variations and "hear". Just as in a microphone, air pressure variations can also cause a speaker to vibrate, which causes the speaker to create a small electrical signal, but not as efficiently as a microphone. In oscilloscope mode, well-rounded, smooth, and repetitive waveforms have nearly all of their energy at a specific frequency. A "square" or "rectangular" waveforms and most music have a series of mathematically-related peaks. A "random" waveform has a frequency "blob" instead of distinct peaks, for example, blowing into the speaker or several people talking at the same time.
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| Speaker connected to PC-interface cable |
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| Voice waveform at 5ms/div |
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| Voice waveform at 0.5ms/div |
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| Frequency spectrum at 5ms/div |
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| Frequency spectrum at 0.5ms/div |
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