Sorry I didn't write about my sound demos last week. The end of the school year is just too busy. Here's the basic list:
I used the function generator to show interference, both constructive and destructive by setting each speaker to a slightly different frequency. You can create some really good beats. When you feed the signal in to Visual Analyzer (VA) you can see the beats as well.
I illustrated destructive interference by setting both speakers to the same frequency and pointing them at my microphone. I slowly changed the distance to the microphone of one of them until the o-scope showed nearly complete destructive interference. If you were ambitious you could use this to determine the wavelength of the sound as well.
Using VA's function generator I generated a frequency tuned to a graduated cylinder to cause it to resonate. I used a cheap $0.50 speaker that was to quite to hear until it was brought near the graduate. You could use this to determine the speed of sound if you were so inclined.
I used a variety of musical instruments to show the different numbers and strengths of relative harmonics using the FFT in VA to illustrate why different instruments sound different even when playing the same note.