Its amazing what you can get students to do, today I got them to put one finger in an ear and shake their heads from side to side. The point of it was to listen for minimums and maximums in sound intensity due to the interference of sound from the two speakers in my laptop. I used the phet fourier transform simulation to produce the sounds and it worked really well. The sound isn't very loud so there wasn't much of a problem with reflection off the walls, The higher the note the closer were the minima. Could probably base a really good practical on it but I don't think it would be so good with 15 students trying to do it at the same time. maybe In could set up my computer at the front and everyone could take measurements on the same sound. Hmm I think i'll get to work on it.