Seeing sound
Visualise the sound wave you are creating as you talk or sink. Do different sounds produce different waves?
As well as seeing the relationships between speed of vibration and pitch, and size of vibration and volume, this allows you to see differences in the sounds you make. The different vowel sounds look different, as do 's' sounds, adult male voices produce much more messy waveforms than do children's voices.
b
Simple version
Effectively just a microphone and oscilloscope that you can talk into.
With timebase
With a digital timebase adjustment, which allows you to start with the dot moving across the screen about once a second, move your hand over the microphone and see that the microphone is measuring air movements. You can then talk and speed up the dot until you can distinguish the waves in speech. It will auto reset if unused for a specified time.