CHM343 DIY - Acoustic Interferometric Determination of the Speed of Sound of Gases

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1	Example Spreadsheet for Acoustic Interferometry DIY Setup - Pchem 'Cloud' Lab
2	Speed of Sound and Heat Capacity Ratio by Acoustic Interferometry
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4	Jeffery L. Yarger, School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604.
5	jeff.yarger@asu.edu or biopchem@gmail.com
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7		August 25, 2021
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9		DIY Setup for Acoustic Interferometry of Air (Data Shown Below)
10		Bought a 1 Ft long 3/4" diameter cPVC Pipe with end caps (Lowes/Walmart/Ace/etc, ~$10). Drill hole in end-caps for earbud speaker on one side and microphone on other side. Any standard set of earbuds and microphone can be used for this DIY setup (~$5 for the earbuds and ~$10 for the lav mic, picture shown below). Audacity software (free) was downloaded and used on a laptop (or tablet / smart phone) to generate noise or chirp and to record the microphone detected sound being played through gas filled tube/pipe for acoustic interferometry. Audacity also has a spectrum analysis tool for FFT of recorded data. A standard rectangular windowing function was used for processing. The FFT data was then saved from Audacity as a text file and imported as the sheet 'Audacity_FFT_65k_Rect_Window_Air_2ft_3_4_in_CPVC_Pipe' for analysis (example shown below).
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24		Figure 1 - Picture of DIY setup on my desk. The cPVC 3/4" tube is ~2Ft long (but 1 ft or less can be used). The lav mic is on
25		the left (USB connection) and the earbud is on the right (3.5mm connection).
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27		DIY Comments:
28		Air is the most natural thing to measure for a DIY home project. However, it is reasonable to get He, CO2, Ar, N2 from common sources for reasonably cheap. I ordered all off amazon. I'm working on an good way to purge and stop flow various gases into the tube/pipe for DIY acoustic interferometry of pure gases such as He, CO2, Ar and N2. It would also be good to find a good DIY way to obtain the measurement at various temperatures (to get the temperature dependence of the sound velocity and hence the heat capacity ratio). My initial idea is to cut it down to 1 ft and just put the entire setup into a refrig, freezer or low setting oven in my house. I could get more sophisticated and use heating tape and a feedback loop thermocouple controlled variable power source, but I kinda like the DIY home appliance idea better. It would help to have a thermocouple to measure the exact temp of the gas in the tube. Also, a better seal will be needed when stop-flow of pure gases is attempted.
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38		On the data science side of this project, this is a great opportunity to teach the basics of FFT, window f(x), automated peak picking, etc. My major delima is trying to use google sheets or excel for this component, vs. a program like matlab, jupyter, etc. Thoughts?
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46	N	Frequency (Hz)
47	1	279.3
48	2	559.5
49	3	837.1
50	4	1113
51	5	1395.6
52	6	1672.9
53	7	1950
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64	Speed of Sound =	340.1568	m/s
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66		Figure 2 - Example data taken from setup shown in figure 1. There is room temperature 'Air' in the tube. Audacity was used to collect
67		the data and also process it to the frequencies shown in the table on the left. This is not meant to provide all the details of measurement
68		but rather just show a quick result as an example that can be easily obtained with a simple DIY setup.
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