Column Editor’s Note: This article is an adaptation of a Britain’s National Physical Laboratory’s “Measurement at Home” experiment.

The speed of sound may be determined using a variety of methods.1–3 Perhaps one of the simplest approaches employs interference.4 Using a pair of wired or wireless earbuds, string (if wireless earbuds are used), a smartphone signal generator application,5 three rolls of toilet paper, and a ruler, it’s possible to determine the speed of sound to within 5% of its accepted value.

To accomplish this, place a toilet paper roll on a tabletop with one of the earbuds at the bottom and center of the roll. Now place the additional rolls on top of the first. This arrangement creates a central hollow tube that will isolate sound produced by the earbuds from ambient noise. Insert the second earbud into the top of the tube and allow it to descend...

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