Single-note echo
| On Museum Hill in Santa Fe, there is a labyrinth paved with green and tan pavers, surrounded by a low circular wall. Of course, this wall produces nice echos when you stand in the center. I noticed that when you clap your hands, the echo contains a clear note (in fact it is a chirped note). I suspected that it had to do with the size of the pavers, so I recorded a few claps with my cellphone. | 
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| Play the sound file: On the right is the frequency spectrum (of the first echo), made with Audacity. There are three clear peaks in the spectrum, the biggest one at 2.9 kHz. Multiply that by the speed of sound, and you get a wavelength. Frequency-to-wavelength calculator
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| The corrugations in the brick pavement favor frequencies that match their spacing. | 
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| 5 brick take up 59 cm, for 11.8 cm per brick.
Perfect match! | 
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Hubert van Hecke Last modified: Mon Mar 29 15:48:56 MDT 2021