Inexpensive alternatives to a number of classic introductory physics sound laboratories are presented including interference phenomena, resonance conditions, and frequency shifts. These can be created using earbuds, economical supplies such as Giant Pixie Stix® wrappers, and free software available for PCs and mobile devices. We describe two interference laboratories (beat frequency and two-speaker interference) and two resonance laboratories (quarter- and half-wavelength). Lastly, a Doppler laboratory using rotating earbuds is explained. The audio signal captured by all experiments is analyzed on free spectral analysis software and many of the experiments incorporate the unifying theme of measuring the speed of sound in air.
References
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Detailed methods for the labs, results, and simulations can be found in the online appendix at: http://faculty.une.edu/cas/jvesenka/scholarship/index.htm.
7.
We used original 3.5-mm wired stereo earphones for Apple iPod, purchased on the web for less than $2/pair. No URL provided since sales location varies.
8.
We used Apple iMac computers and have successfully tested these experiments on Apple PowerBooks and HP Pavilion laptops as well. The key feature is a decent quality internal micro phone in the computer. Without this, some experiments may not produce good results.
9.
Can be found on the web for less than $1 each.
10.
Audacity version 2.1.0 for PC or Mac, http://audacity.sourceforge.net.
11.
The iPhone program originally used in this paper (Stolltech audio signal generator) is no longer available. Other free tone generators are available that work equally well though, such as Physics Toolbox Tone Generator, https://itunes.apple.com/us/app/physics-toolbox-tone-generator/id998187454?mt=8.
12.
There are many options for Android phones as well: https://play.google.com/store/search?q=audio%20signal%20generator&c=apps&hl=en, of which the Physics Toolbox Sensor Suite is our preference, found at https://play.google.com/store/apps/details?id=com.chrystianvieyra.physicstoolboxsuite&hl=en or the portable version of Audacity, http://download.cnet.com/Audacity-Portable/3000-2170_4-10608458.html.
13.
For directions on how to use Audacity, see http://manual.audacityteam.org/o/.
14.
To place a position axis over the recorded image, students can “print screen” the image and paste into an editing program such as Microsoft Word, using their analysis of speed and time to know where distances should match up with parts of the interference patterns.
15.
Out-of-phase speakers are most commonly the result of incorrect wiring. One way to check for polarity-flipped speakers is to hold them equidistant from the microphone and then slowly shift both either to the right or left and see if the amplitude decreases (in phase) or increases (out of phase).
17.
This inexpensive ruler tape is about $0.18 for every 30 cm and can be found at this temporary location: http://www.amazon.com/gp/product/B002E3IFUS/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1.
18.
L. E.
Kinsler
, A. R.
Frey
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Coppens
, and J. V.
Sanders
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, 3rd ed., (Wiley
, New Jersey
, 1982
).© 2016 American Association of Physics Teachers.
2016
American Association of Physics Teachers
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