Sound as the composition of multiple frequencies

Everybody knows the rainbow!!!! When raining, the "white" light from the sun is passing through the drops of water. Each drop acts as a prism. Then we can see that the white light is entering the "prism" but on the other side it is possible to see that rays from different colours (frequencies) emerge other side.

What does it mean? THe short answer is that the phenomenon we understand as "white" light is in reality, the combination of all the colours as shown in the picture below



If instead of "white" light we illuminate a prism with laser pointer, a monochromatic (one frequency) light, we can follow how the ray is refracted and reflected but the emerging colour is the same colour that the incident one.



The same principle is happening with sound. Lets sample a tuning fork. This tool produces only one frequency when it vibrates. See the movie below

Click here to see the Movie

To summarize, it is possible to see that the tuning fork produces a sinusoidal sound wave and it produces only one frequency - only one peak in the spectrum analyzer.

Lets explore what happens when the sound is NOT a tuning fork, for example our voice

Click here to see the Movie

From the sample of our voice it is possible to see that it is NOT a pure sine wave, and from the spectrum analyzer it is possible to see that there is MORE than one peak, meaning that the sound that of our voice is the composition of multiple sound waves acting at the same time on the eardrum.
This phenomenon is called Interference.

In conclusion, the Spectrum analyzer can show us the different frequencies that are included in a sound we perceive.
The first peak receives the name of the FUNDAMENTAL frequency with a frequency of f1 and the other peaks receive the name of HARMONICS. Each harmonic has its place and its frequency for example the second peak receives de name of Second Harmonic and its frequency will be f2, the third peak will be the Third Harmonic with a frequency f3, etcetera.



Now it is time to start to do our own experiments. For this matter you will need to have a Spectrum Analyzer handy and to know how to use it. Lets move to the next activity by clicking on the arrow on the right botton of the screen.





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