Abstract
Add two sine waves. Display the signal versus time, the Fourier Power Spectrum, and play the resulting sounds on computer speaker.
Portable
Yes
Principles Illustrated
Combining waves. Beats. Fourier Power Spectra.
NCEA & Science Curriculum
PHYS 3.3
Instructions
The following commentary relates to an existing demo at VUW but it can provide the basis of a demo for teachers to try in the classroom.
Launch the simulator from the program menu. Adjust the frequency of the first signal and its amplitude (0-255). Press the Sound button to play the sound on the computers speakers. You can adjust the horizontal scale on the graph to zoom in and see the individual wiggles. Just select the last number or first number on the axis and type in a new number. Next, add a second frequency and amplitude. For example, set the first sound to 1000 Hz and an amplitude of 100. Set the second to 1010 Hz and an amplitude of 100. You can then hear beats. As an alternative, combine two frequencies that are quite different such as 500 Hz and 5000 Hz with different amplitudes.
Press the FFT button to see a Fourier Power Spectrum of the signal. Again adjust the axes to zoom in and see one or two peaks depending on the signal. Note that the Fourier Power Spectrum of a sine or cosine pulse is the square of the sync function centred at the nominal sine wave frequency. The signal data has been zero filled to make the Power Spectrum smooth.
SYSTEM REQUIREMENTS
Requires at least an XGA display (1024 x 768).
Safety
Individual teachers are responsible for safety in their own classes. Even familiar demonstrations should be practised and safety-checked by individual teachers before they are used in a classroom.
Related Resources
Beats || SquareWave || Wave Simulator Software
Teaching Resources
Would you like to contribute lesson suggestions? Contact us.
Credits
This teaching resource was developed with support from
The MacDiarmid Institute
Faculty of Science, Victoria University of Wellington
School of Chemical and Physical Sciences, Victoria University of Wellington