Measure Speed of Sound With Audacity!

What is sound? Sound is mechanical wawe, which travel in air (or any medium) with some speed. Our ears detect pressure from molecules, which travel in air in a form of mechanical wawes. In this project, I will show you, how to measure speed of sound with Audacity, microphone and pipe.

This project can be used for laboratory work. It includes physics ( lecture about sound, wawes), technology (audacity, microphone).

For measure speed of sound, I use simple method. I calculate how many meters travel sound during measured time. For that, you need:

1 x pipe, I use from metal broom

2 x bigger book for better grip pipe, it is not good, when pipe lay on table

1 x microphone

2 x spoon for making sound

1x installed Audacity for measure sound (it is free, http://www.audacityteam.org/download/)

First of all, prepare experiment, prepare microphone, bring it closest to one end of pipe. Also, put pipe into books, like on photo, for better manipulating and results.

Then press recording button on Audacity, and make sound - click with spoons on second end of pipe. Try to make more clicks, with different magnitude and length. Length should be as short as possible, but also with enough decibels.

I prepare waw file for you to test.

So try to make sound, and how to get speed of sound, I describe in next step.

So, first view on Audacity, we can see a lot of short clicks, you can choose one, and zoom to it in Audacity. Then you must find individuals peaks of one click. Choose 2 peaks (except first one), and write down their time. I choose two:

one with time 3.1838 seconds, and second with time 3.17823 seconds. Then just substract both times to get length of two peaks: my length = 3.1838 - 3.17823 = 0.00557 seconds. That is time, how long sound travel from one end of pipe to second and back.

Explanation: when you make sound with spoon at one end (let's mark as B), sound travel in pipe to end A to microphone. Then microphone detect it, computer remember time. Sound just reflect from this A end and continue to again to B. And then again reflect from B end, and travel to A..., sound always reflect. And that reflections are our peaks in Audacity. Important is, make clear signal, and good, readable peaks which we can recognize in Audacity.

And what is speed of sound? Speed in general equal distance divided byt time. To calculate speed of sound, I measured also length of pipe, it is 95 cm, or 0.95 meters. Don't forget, you must add 2 times length of pipe, because sound travel from one end to another and BACK! Speed:

speed of sound = length / time = 2*0.95 / 0.00557 = 341.12 m/s.

Speed of sound depend on temperature, I measure in rooms, so around 340 m/s is good, accorind this tables:

https://en.wikipedia.org/wiki/Speed_of_sound#Tables